efficient catamaran hull design

Did You Know That We Offer Contract to Closing Services? Click Here to Find Out More.

Need Marine Financing? Apply Here With Our Partner, First Approval Source

• Catamaran Interviews
• Catamaran Reviews
• Buying Advice
• Selling Advice
• Woods Design Advice
• Americat 3014
• Balance 526
• Bali 40 Catspace
• Beneteau Blue II
• Broadblue 346
• Broadblue 38 Prestige
• Broadblue 385
• Broadblue 435
• Broadblue 46
• Catalac 10M
• Catalac 11M
• Catalac 12M
• Catalac 900
• Catana 42 S
• Chris White 48 Voyager
• Chris White 55
• Corsair F28 R
• De Villiers
• Dolphin 460
• Endeavour 30
• Endeavour 35 Victory
• Endeavour 36
• Endeavour 44
• Endeavour 44 TrawlerCat
• Fortuna 36 Island Spirit
• Fortuna 401 Island Spirit
• FP 32 Maldives
• FP 35 Tobago
• FP 37 Antigua
• FP 38 Athena
• FP 39 Fidji
• FP 40 Lavezzi
• FP 40 Lucia
• FP 40 Summerland MY
• FP 41 Lipari
• FP 42 Astrea
• FP 42 Venezia
• FP 43 Belize
• FP 44 Helia
• FP 44 Orana
• FP 46 Bahia
• FP 46 Casamance
• FP 48 Salina
• FP 56 Marquises
• FP 57 Sanya
• FP 60 Eleuthera
• FP Saona 47
• Gemini 3000
• Gemini 3200
• Gemini 3400
• Grainger 420 Mystery Cove
• Hirondelle 7M
• Lagoon 37 TPI
• Lagoon 42 TPI
• Lagoon 43 PC
• Leopard 39 PowerCat
• Leopard 45 Classic
• Leopard 47 PowerCat
• Leopard 51 PowerCat
• Leopard 53 PowerCat
• Maine Cat 30
• Maine Cat 41
• Matrix 450 Vision
• Matrix 760 Silhouette
• Maverick 400
• Maverick 420
• Maverick 440
• Nautitech 40
• Nautitech 442
• Nautitech 46 Open
• Nautitech 47
• Outremer 40
• Outremer 45
• Outremer 50 Standard
• Outremer 55
• Privilege 37
• Privilege 39
• Privilege 42
• Privilege 43
• Privilege 435
• Privilege 45
• Privilege 465
• Privilege 48 Transcat
• Privilege 482
• Privilege Serie 5
• Prout 31 Quest
• Prout 33 Quest
• Prout 34 Event
• Prout 35 Snowgoose
• Prout 37 Snowgoose
• Prout 37 Snowgoose Elite
• Prout 38 Manta
• Prout 39 Escale
• Royal Cape 45
• Royal Cape 530 Majestic
• Royal Cape Majestic 500
• Sailcraft 30 Iroquois
• Sailcraft 32 Comanche
• Sailcraft 35 Cherokee
• Sailcraft 41 Apache
• Sailcraft 44 Apache
• Wildcat 350
• Seawind 1000
• Seawind 1160
• Seawind 1200
• Seawind 1260
• Seawind 1600
• Solaris 36 Sunrise
• Solaris 36 Sunstar
• St Francis 44
• St Francis 48
• St Francis 50
• Stealth 11.8
• Heavenly Twins 26
• Ocean Twins 38
• Voyage 380 Maxim
• Voyage 400 Norseman
• Voyage 430 Norseman
• Voyage 450 Cabriolet
• Voyage 47 Mayotte
• Wharram 38 Tiki
• AMI 320 Renaissance
• Woods 22 Wizard
• Woods 35 Banshee
• Woods 35 Flica
• Woods 36 Scylla
• Woods 36 Vardo
• Woods 38 Transit
• Woods 40 Meander
• Xquisite X5
• Xquisite X5+

Catamaran Hull Design

• Post author By Rick
• Post date June 29, 2010
• 2 Comments on Catamaran Hull Design

Part 1: Notes from Richard Woods

Since the America’s Cup experimented with going multihull, there’s been a lot of interest in catamaran performance and the catamaran hull designs that define performance. Many guys are investigating whether to buy a catamaran or design and build their dream boat. Let it be said here that building a large catamaran is not for the faint of heart. People begin building 100s of boats a year, yet few are ever completed, as life always seems to have a way of interfering with a good boat build. 

Never the less, since the rest of this website is about selecting and buying a boat , it only seems fair to have at least one webpage that covers catamaran design. This page contains notes on boat hull design goals and an accompanying page from Terho Halme has mathematical formulas used in actual catamaran hull design. It has become a popular research stop and an important reference to the catamaran design community.

The content of this page was reproduced from the maestro of Catamaran designs, renown British naval architect, Richard Woods, who not only designs catamarans, he sails them across oceans…. repeatedly. He has a lot to say on the subject of catamaran hull design.

“…When it’ all said and done, the performance of a sailing catamaran is dependent on three primary specs: length, sail area and weight. If the boat is longer it generally means it’ a faster boat. If she has more sail area, it means she’ a faster boat and if she’ light it means she’ a faster boat.  Of course, there are limits: Too much sail area capsizes the boat in brisk winds. If the boat is designed too light, she will not take any kind of punishment. Too slim a hull design and the boat becomes a large Hobie Cat capable of only carrying your lunch. Of course, too long and large and you’d have to be Bill Gates to afford one. Then there are lot of additional and very important factors like underwater hull shape, aspect ratios of boards and sails, wet deck clearance, rotating or fixed rigging and so on….” Richard Woods

All Catamarans are not equal, but all sailboats have two things in common: They travel on water and they’re wind powered, so the Catamaran design equations in the 2nd part should apply to every catamaran from a heavy cruising Cat to a true ocean racer.

Richard Wood’s comments on catamaran design:

We all know that multihulls can be made faster by making them longer or lighter or by adding more sail. Those factors are the most important and why they are used as the basis of most rating rules. However using just those figures is a bit like determining a cars performance just by its hp and curbside weight. It would also imply that a Tornado would sail as fast forwards as backwards (OK, I know I just wrote that a Catalac went faster backwards than forwards)

So what next?? Weight and length can be combined into the Slenderness Ratio (SLR). But since most multihulls have similar Depth/WL beam ratios you can pretty much say the SLR equates to the LWL/BWL ratio. Typically this will be 8-10:1 for a slow cruising catamaran (or the main hull of most trimarans), 12-14:1 for a performance cruiser and 20:1 for an extreme racer.

So by and large faster boats have finer hulls. But the wetted surface area (WSA) increases proportionately as fineness increases (for a given displacement the half orange shape gives the least WSA) so fine hulls tend to be slower in low wind speeds.

The most important catamaran design hull shape factor, is the Prismatic Coefficient (Cp). This is a measure of the fullness of the ends of the hull. Instinctively you might think that fine ends would be faster as they would “cut through the water better”. But in fact you want a high Cp for high speeds. However everything is interrelated. If you have fine hulls you can use a lower Cp. Most monohulls have a Cp of 0.55- 0.57. And that is about right for displacement speeds.

However the key to Catamaran design is you need a higher Cp if you want to sail fast. So a multihull should be at least 0.61 and a heavy displacement multihull a bit higher still. It is difficult to get much over 0.67 without a very distorted hull shape or one with excessive WSA. So all multihulls should have a Cp between 0.61 and 0.65. None of this is very special or new. It has been well known by naval architects for at least 50 years.

There are various ways of achieving a high Cp. You could fit bulb bows (as Lock Crowther did). Note this bow is a bit different from those seen on ships (which work at very specific hull speeds – which are very low for their LOA). But one problem with them is that these tend to slam in a seaway. 

Another way is to have a very wide planing aft section. But that can increase WSA and leads to other problems I’ll mention in a minute. Finally you can flatten out the hull rocker (the keel shape seen from the side) and add a bustle aft. That is the approach I use, in part because that adds displacement aft, just where it is most needed.

I agree that a high Cp increases drag at low speeds. But at speeds over hull speed drag decreases dramatically on a high Cp boat relative to one with a low Cp. With the correct Cp drag can be reduced by over 10%. In other words you will go 10% faster (and that is a lot!) in the same wind and with the same sails as a boat with a unfavorable Cp. In light winds it is easy to overcome the extra drag because you have lots of stability and so can fly extra light weather sails.

The time you really need a high Cp boat is when beating to windward in a big sea. Then you don’t have the stability and really want to get to your destination fast. At least I do, I don’t mind slowly drifting along in a calm. But I hate “windward bashing”

But when you sail to windward the boat pitches. The sea isn’t like a test tank or a computer program. And here I agree with Evan. Immersed transoms will slow you down (that is why I use a narrower transom than most designers).

I also agree with Evan (and why not, he knows more about Volvo 60 design than nearly anyone else on the planet) in that I don’t think you should compare a catamaran hull to a monohull, even a racing one. Why chose a Volvo 60/Vendee boat with an immersed transom? Why not chose a 60ft Americas Cup boat with a narrow out of the water transom?? 

To be honest I haven’t use Michelet so cannot really comment. But I have tested model catamarans in a big test tank and I know how inaccurate tank test results can be. I cannot believe that a computer program will be better.

It would be easy to prove one way or the other though. A catamaran hull is much like a frigate hull (similar SLR, L/B ratios and Froude numbers) and there is plenty of data available for those. There is also a lot of data for the round bilge narrow non planing motorboats popular in the 1930’-50’s which again are similar to a single multihull hull.

One of the key findings I discovered with my tank test work was just how great the drag was due to wave interference between the hulls. Even a catamaran with a modern wide hull spacing had a drag increase of up to 20 % when compared to hulls at infinite spacing. One reason why just flying a hull is fast (the Cp increases when you do as well, which also helps). So you cannot just double the drag of a single hull and expect to get accurate results. And any speed prediction formula must include a windage factor if it is to give meaningful results.About 25 years ago we sailed two identical 24ft Striders next to each other. They were the same speed. Then we moved the crew of one boat to the bow. That boat IMMEDIATELY went ½ knot faster. That is why I now arrange the deck layout of my racing boats so that the crew can stay in front of the mast at all times, even when tacking or using the spinnaker.

I once raced against a bridge deck cabin catamaran whose skipper kept the 5 crew on the forward netting beam the whole race. He won.

Richard Woods of Woods Designs www.sailingcatamarans.com

• Tags Buying Advice , Catamaran Designers

Owner of a Catalac 8M and Catamaransite webmaster.

2 replies on “Catamaran Hull Design”

I totally agree with what you say. But Uli only talk sailing catamarans.

If only solar power. You need the very best. As limited watts. Hp.

The closer to 1-20 the better.

Closing the hulls to fit in cheaper marina berth. ?

You say not too close. But is that for sailing only.

Any comment is greatly appreciated

Kind regards Jeppe

Superb article

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Save my name, email, and website in this browser for the next time I comment.

A Trusted Source For Boating Information Since 2019

Catamaran hulls- everything you need to know.

• Post Written By: Boater Jer
• Published: July 17, 2022
• Updated: July 19, 2022

Disclaimer: You might notice that we recommend products in some articles. We may earn a commission for referring you if you click the link and buy a product.

We only recommend products we’ve tried/tested/own (that’s why you won’t find thousands of affiliate links on my site). If you have experience with one of the products we’ve mentioned, please share your experiences in the comments at the end.

Advertisement

Catamaran hulls are not like normal boats but provide increased stability. Let’s take a look at these incredible boats and how their hulls create one of the most versatile watercraft available today.

The Tamil Cholas used catamarans to ferry their troops to invade Malaysia, Indonesia, and Burma. The early paravars or fishing communities in the southern part of Tamil Nadu used two-hulled boats to fish. Polynesian seafarers were also early users of the catamaran, utilizing the watercraft to get to hard-to-reach islands. ( source )

Although the catamaran hull concept is a relatively new introduction to modern boat design , the boat has been in use since the 5th century. It was used for fishing, traveling, and transporting people and supplies. 

Parts Of A Catamaran

Here are the basic parts of the modern sailing catamaran:

• Hulls are what sets this boat apart from the rest. The catamaran has two hulls, while the monohull, as the name suggests, has only one hull. Most of the advantages of this boat are hinged on these two hulls. 
• The bridge deck connects the two catamaran hulls. 
• On top of the catamaran hulls and the bridge deck is the deck . It is where owners attach most of the equipment in a boat. 
• You can locate the berth, the galley, and other living amenities in the cabin . 
• The cockpit is where you find the navigation equipment of the boat . It is where you control the catamaran’s rudder, sails, and engine. 

Types Of Catamaran

The modern catamaran is far more different than its crude ancestor. Instead of tree cutouts, catamarans are now carbon fiber or fiberglass. Here are the different types of catamarans: 

Based On function

Pontoons are usually present on rivers and lakes and sometimes even on oceans, but they only travel near the shore.

In a catamaran pontoon-type boat, the pontoons serve as storage areas, where you will find the onboard motors. They are useful for water leisure activities such as short water trips, tubing, wakeboarding, and water skiing. 

Some pontoons may also serve as houseboats. They provide a broader, more stable platform ideal for a floating house. Plus, the space is bigger, and most of it is above water. It offers a better viewing option than a monohull. ( Source )

Small Waterplane Area Twin Hull is a catamaran-type boat that the United States Navy initially used for military purposes. They provide the water stability that is necessary when transporting heavy military equipment. 

One example of a military SWATH catamaran is the Spearhead class EPF. It is as long as a World War II escort destroyer, yet it is twice as fast at 43 knots. It can reach that speed because of its two separate hulls.

Because of their innate speed, SWATH catamarans can become patrol boats in lakes and rivers. They can easily outrun and outmaneuver standard watercraft.  

Nowadays, there are SWATH cruise ships and other non-military variations. ( Source )

Based On Design

• Sailing Catamaran

The smaller sailing catamarans do not have auxiliary engines, so the owner can propel the boat by harnessing the wind using the sails. It’s a popular choice for people with very little or no sailing experience because they are light and easy to use. 

The larger sailing catamarans are for group charters and long-distance cruising. They have become so popular lately that they now outnumber monohulls in tropical locations all over the world. They have a last, a headsail, and a mainsail. And the twin hulls have one engine each. 

• Power Catamaran

Unlike their sailing cousins, the powered catamarans do not have sails. They have massive engines which provide high speed. Their twin hulls are stronger and can carry and protect the large motors. 

The smaller “powercats” are used mainly for fishing. The bigger ones are rented out for charters and cruises. 

Catamaran Hulls Performance 

Thanks to the catamaran hulls, the boat offers many advantages over other boat types. 

• Because its dual-hull design provides a broader base, it offers more water stability than monohull boats. It makes the cat (catamaran) a popular choice for fishing expeditions and cruises.
• Riding a catamaran is ideal for people who feel seasick whenever they ride boats. The twin hulls prevent the boat from moving from side to side. The hulls allow the boat to travel smoothly, even on moderately choppy waters.
• The catamaran is the best choice when storing provisions and other household items with less heeling and bobbing. 
• The twin hulls’ stability is ideal for many activities such as cooking and partying. 
• Cats offer more moving space because of their broader base, thanks to dual hulls.
• With a catamaran, you have two great options on where to hang out. You can do it on the spacious deck or below the galley. 
• Compared to a monohull of the same size, the catamaran can accommodate more equipment and people.
• The living area in a catamaran is above the water line. This feature provides more natural light, a greater view of the outside, and better air circulation. 
• Since catamarans do not have keels, they can anchor on shallow waters, something that most monohulls will not be able to do. This ability of catamaran boats is impressive, especially if you are going around areas with many reefs and small islands.
• Catamaran hulls allow the boat to cut through the waves easier and faster. It means they require less engine power than their monohull counterparts.
• Because it has two engines and two rudders, the catamaran can easily maneuver in very tight spaces. 
• Because they do not carry heavy keels, catamarans can sail faster than monohulls. 
• The catamaran’s stability, speed, and weight make it a safer option than the monohull. It can sail in shallow waters, make a 360 degrees maneuver effortlessly, and carry more provisions. 

Disadvantages Of A Catamaran

Like any other boat type, the catamaran also has drawbacks and limitations. Here are some of them:

• The catamaran hulls prevent the boat from sailing as fast as the monohull upwind. The two hulls cause drag, and this slows the boat considerably. 
• Because of its bigger size, looking for a docking site can be more difficult and costlier than a monohull. 
• For hardcore sailing fans, the experience of sailing with a catamaran will never be able to match that of sailing with a monohull. To them, the challenge of true sailing is just not there with a catamaran.

What Are The Hulls Of The Catamaran Called?

According to the Online Etymology Dictionary, the Tamil word கட்டுமரம், which is pronounced as kattumaran, is where the word catamaran takes its name. The word means “pieces of logs tied together”. Through the years, the term has evolved into what is now a catamaran in English. 

What Are The Characteristics Of A Catamaran Hull?

• Both hulls of a catamaran complement each other to achieve very minimum water resistance. 
• Because of this, it takes less energy to propel a catamaran, whether via an engine or sails. 
• The catamaran hulls provide stability to the boat. The twin-hull significantly reduces bobbing. 
• The catamaran’s ability to keep steady on the water makes it an ideal vessel for cooking, dining, and storing provisions. 

Are Catamarans Good In Rough Water?

Catamarans are amazingly stable in rough water. The catamaran’s design and build, which provides stability, are factors why it is one of the best boats to use when the waters are choppy. 

Yes, catamarans are relatively more expensive than monohulls. Nevertheless, since single-hull boats are less expensive, their resale value is also cheap. 

If you add all the advantages that a catamaran offers – safety, comfort, and speed- it does not come out expensive. 

patekphilippe.io

Share this post with your friends

Subscribe to our newsletter.

Join us in our love for all things water. And Adventure.

Why Are Boat Steering Wheels So Big?

Advertisement You see them on the water in summer or all year round, depending on where you live, boats, and lots of them. Riding on the water on a ship is calming and relaxing unless you are racing, then it can be exhilarating and action-filled! I have been on many boats of different shapes and

Are Catamarans Safe In Rough Seas?

Catamarans are known to be reliable and fun to operate. From the personal watercraft sized cats to the massive superyacht class of catamaran, all are great ships of the seas. But are catamarans safe in rough seas?

Pontoon Boats Vs. Catamaran (Pros and Cons For New Buyers)

Advertisement Pontoon Boats Vs. Catamaran – Pros and Cons For New Buyers – A Boating Guide Buyer’s Guide For 2023. Would you like to know the differences between pontoon boats and catamarans? These two vessels seem similar in the hull design to stay on the water. However, there are several differences, and each ship is

Boat Hull Types – Which Boat Hull Is Best?

In this article, we examine all these hull types with full explanations of how each one works so you can figure out which is best suited for you.

A Guide To Choosing Your First Boat

Advertisement A Guide To Choosing Your First Boat – A Boating Guide Buyer’s Guide Report for 2023. Would you like to buy your first boat? When you buy a boat for the first time, it is easy to make a mistake due to the lack of experience. Therefore, before making any decision, you must evaluate

PowerSeeker Intelligent Fish Finder – A Smart Fishing Gadget

Advertisement PowerSeeker Intelligent Fish Finder Review Do you love fishing? Who doesn’t? Fishing is not an easy task, especially if you’re out on a trip with your friends. It’s because, at such times, it becomes a matter of pride to quickly catch a vast fish.  Mostly, people find it hard even to trace a fish.

Boat Information By Type

© 2023 Boating.Guide, A Hyperwave Media Group Ltd. Publication.

Privacy Overview

Log in or Sign up

You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser .

What's the best shape for a fast & efficient catamaran hull?...

Discussion in ' Boat Design ' started by Seagem , Jan 21, 2009 .

Seagem Junior Member

Doing research on fast & efficient hull shapes for a 25' cruising catamaran capable of 22/25 knots cruise and 30 knots top speed, while still providing reasonable performance at lower speeds, I found the following: 1) Efficient planning shape, foil assisted:Corsair 22 Foiler The boat does 50 mph top with twin 90hp motors and cruises happily at 30 mph with better than 3 miles/gallon fuel consumption. Its asymmetrical hull design allows it to bank in turns, unlike most other catamarans.. Description: http://floridasportfishing.com/magazine/product-reviews/boats-reviews/corsair-foiler-2200.html Potential drawbacks: not efficient at displacement speeds 2) Efficient displacement hull: Prowler 9 meter Description: http://www.schionningmarine.com.au/www/page.cfm?pageID=195 Twin 50hp outboards will cruise this catamaran at 17 knots using 1 liter/mile or 3.8 miles /gallon with top speed of 21 knots, thanks to a fineness ratio of 15 to 1... Drawback: Top speed cannot exceed 23 knots, as this is a displacement hull... 3) Not so efficient semi-displacement hull: VT650/950 The larger version of this design with the unusual asymmetric chines, the VT950 cruises at 17 knots, using 2.2 liters/mile (1.7 mile/gallon) and tops out at 26 knots with twin 140hp outboards. Many advantages: sharp entry at slow or high speeds, load carrying ability aft where the weight is usually concentrated, easy access to hulls from bridgedeck and clever location of the outboard engines, which have a clear water flow while keeping the stern platforms free. This also moves the engine weight and prop further forward, reducing potential aeration in rough seas. Description: http://www.schionningdesigns.com.au/login/pages/images/StudyPlanProwler950VT.pdf One major drawback: the hull shape has too much wetted area which affects its efficiency. I suggested tapering the "V" section to nothing about one third before reaching the stern, but Schionning says it increases the drag... 4) Efficient semi-displacement hull: Chilkat 30 This boat cruises at 30 knots with 3 miles/gallon fuel efficiency and tops out at42 knots with twin 225hp outboards. However, it still cruises at 25 knots and tops out a 43 mph with twin 150's... Description: http://www.blackfeatherboats.com/power_catamaran_boat.cfm Drawback: the bridge deck may be too low and pound in a seaway... There is also the Sea Knife hull design which may be suitable, but will require some expensive R&D to make work satisfactorily: http://www.yachtforums.com/forums/technical-discussion/2701-trimarans-bladerunner-4.html Any suggestions of hulls that might fit the bill would be welcome...  

sabahcat Senior Member

Are you still trying to get queen sized beds, dinettes, shower toilet and a few hundred litres of water onto these hulls? Does it still need to be a trailerable width? If not, option 1 although I would suggest a boat with foils may not have got the hull shapes right to start with. If you want the beds etc then option 2, but like was said in your other thread, it will be high sided due to bridgedeck clearance. Thems the rules.  

Good question.... sabahcat said: ↑ Are you still trying to get queen sized beds, dinettes, shower toilet and a few hundred litres of water onto these hulls? Does it still need to be a trailerable width? If not, option 1 although I would suggest a boat with foils may not have got the hull shapes right to start with. If you want the beds etc then option 2, but like was said in your other thread, it will be high sided due to bridgedeck clearance. Thems the rules. Click to expand...

mark775 Guest

There is a Chilkat thing here and the owner loves it but the outboards are ripping the the back of the boat off... Most in this neck of the woods have given up on little cats that plane, by the way because of the hobby-horsing and general thrashing.  

terhohalme BEng Boat Technology

http://glacierbaycats.com/show  

robherc Designer/Hobbyist

Hmmm... I know you don't like the speed limit of a displacement hull, but it's going to be by FAR your most efficient through-the-water (at least under varied speeds). If I were to build a boat for myself, with the same qualifications you listed, I'd be tempted to go with fine, mostly-displacement hulls (if not fully displacement), but I'd still foil-assist it. With the foil-assist, you can dramatically reduce the displacement of the hull, and thus the wetted surface, w/o having to plane, so that seems like the way to go for me...but I still prefer to sail also, so the efficiency thing is pretty paramount to me, while I'd be quite happy with 25knots...and 0litres/nautical mi.  

Seagem said: ↑ The hulls are a cleverer design than appears at first sight: notice the main chine coming down the bow and turning down below the slightly convex bottom to prevent the lifting water flow under the hull from escaping sideways. Also the other chine just above the waterline that has a rubbing strake: the fineness ration is a narrow 18 to 1... Click to expand...

eponodyne Senior Member

I'd go with option 2. 20 knots is really hauling bass, let's not forget that 20 knots hour after hour adds up to 550 statute miles in a day. How far do you really need to go, and how fast do you really need to get there? Who are you really trying to impress?  

mark775 said: ↑ There is a Chilkat thing here and the owner loves it but the outboards are ripping the the back of the boat off... Most in this neck of the woods have given up on little cats that plane, by the way because of the hobby-horsing and general thrashing. Click to expand...

Seagem said: ↑ As mentioned earlier, the boat is 25' plus the swim platform, which will give a total of close to 27' and it may be necessary to still go longer to help carry the fairly substantial tankage necessary... Click to expand...

Alik Senior Member

From our experience, hull shape is secondary issue (unless it is too bad or not match the desired speed). Weight - this is key point of fuel efficiency. Make Your boat light to be fuel efficient. For planning cat, a lot of weight savings can be obtained by light bottom. Say, using AirexR63 and Kevlar/E-glass composite on bottom will give 1200 kg of hull structure for 10m cat, while for normal WR/CSM the weight is 1900 kg.  

Seagem said: ↑ A foil addition remains an option and it has been done successfully on a 46' displacement cat built by Alwoplast as a retrofit: speed increased by an amazing 35%... The fastest I was ever able to sail my Antigua 37 catamaran under spinnaker alone on an Atlantic crossing to the Caribbean was 15 knots: above that, the bows started to bury and waves would reach the foot of the mast by the time I took down the spi. Click to expand...

The Chilkat is by Black Feather Boats. It was an option pic posted above.  

50' Wave piercer by Gold Coast yachts on St Croix... Please, click on the link below to enlarge the photo and see the lay-out... 50' Wave piercer by Gold Coast yachts on St Croix... Owners comments: Mosler claims his boat burns 3 gph at 10 knots for 3.33 nmpg and 11.1 gph at 20 knots for 1.80 nmpg. His top speed is over 26kts with a 24kt cruise with the d3's Volvo 190hp at just over 14 gph. The length to beam of each of my hulls is about 16:1, and the bridge deck is about 3ft over the surface at the rear, sloping up towards the bow, so it can quarter some very high seas at full cruise without slapping, though the wind will blow a lot of spray on the upper aft deck at high speeds. Warren Mosler said: I took 13 people to St. Thomas from St. Croix yesterday quartering 8 ft seas at about 20 kts. picked 4 in St Thomas, had lunch in St. John, back in St. Croix less then 2 hours later. All sat comfortably on the upper aft 'sundeck' above the aft berths (and no one got sea sick). http://pmyeditors.blogspot.com/2008/01/is-it-finally-happening-are-power.html  

• Advertisement:

And your point? 25feet has grown to 50feet? Similar concept Sheer Khan http://www.charterworld.com/index.html?sub=yacht-charter&charter=luxury-catamaran-sher-khan-715 http://www.incat.com.au/  

Attached Files:

Obrwavepiercer2.jpg, catamaran_united_states_navy_usn_joint_venture_hsv_x1.jpg.

What's the biggest mast that a home/backyard builder could make?

What's that thingy?

Newbie Here. What's wrong...

what's this used for ?

what's up with these 'inverted' strakes on Tarpon 160 SOT kayak?

what's name of this construction？

Please...What's this boats design?

What's Next

What's the two ship design spiral other than Evans design spiral

Human powered cargo boat - what's possible?

• No, create an account now.
• Yes, my password is:
• Forgot your password?

PROA HULL DESIGN

The advantages of proa hull design.

Setting out with the goal of building the most efficient boats we could, our founder Larry Graf and his designers sought to create earth-friendly cruisers that would inspire a new generation of boaters. And because Larry and his team played a hands-on role in developing some of the world’s best catamarans, they had an idea of what a boat could be in terms of comfort, stability, and fuel economy.

When one looks at catamarans vs. monohulls, the starting point is clear. The many advantages catamarans exhibit when compared with monohulls are an excellent starting point. Catamarans offer a stable ride with predictable hull movement. The seakeeping is excellent, even in rough conditions. Another advantage the design provides: incredible onboard space. The space of a catamaran is often comparable to that of a monohull that is 25 percent longer. Catamarans also have been proven to provide efficient operation.

A Different Kind of Catamaran

The concept was formed, and extensive testing was done to both prove and refine the design until the hull form we have today was established and then patented.

The first boats were single-engine diesels, with all propulsion confined to the larger starboard hull. This hull has the appendages including a keel, prop, and rudder. The hull forms are hydrodynamically designed so that power on one side creates straight tracking when the rudder is centered. If it were not for this, and rudder was needed to make the boat track straight, the constant rudder movement would create additional drag. The proa hull form works efficiently with both inboard and outboard power. Performance and stability remain unmatched whether powered by a single diesel or two gas outboards.

The shape of the tunnels from fore to aft is also precisely crafted. The forward section is designed to cut through wave tops, when in extreme conditions, creating a slight amount of lift as the vessel enters the wave with no slapping. The water funnels back into the tunnel flowing evenly and exiting at the stern. This tunnel design keeps water flowing and reduces wave impact much better than the tunnels of other catamarans.

The wider starboard hull provides more space for the accommodations, and also makes it easier to access and manage the engine and machinery. The proa hull on the portside is 35 percent narrower, but its actual drag is reduced by approximately 50 percent due to fluid dynamics. A hull that is a little thinner maintains the buoyancy required to keep the boat running true but requires a lot less energy to move through the water. This makes a big difference in efficiency.

Our patented proa design for inboards uses just one engine, one shaft, one prop, one rudder, and one keel—half the typical engine appendage drag of a twin-engine design. The hulls are shaped to compensate for the engine torque. Since both fluid-dynamic and engine-torque forces are proportional to speed, the boat runs straight at every speed. Even better, the single-engine design saves dramatically on machinery weight, which in turn, saves on the required structural-component sizes and fuel needs, and their corresponding weight. This reduces the boat’s weight by around 44 percent. Less weight also equals much less drag. Thanks to solid engineering principles and innovation, our boats strike the perfect balance for the environment: comfortable and efficient.

A second round of innovation was conducted on the outboard-powered boats. Originally the second engine was to allow for a trolling motor, but testing and further refinement led to the two-engine configuration. By thinking even further outside the box, we created an asymmetrical installation that has not been seen previously: one 200-horsepower Yamaha on the larger hull, matched to a 70-horsepower outboard on the smaller hull. With the option to run on both engines or on the single larger outboard, or even just on the smaller outboard, we are able to see the advantages in efficiency.

Patent No. US 8,109,221 B2

Stay Up to Date with Aspen Sign up to receive our enewsletter.

11656 Knudson Rd. Burlington, WA 98233

Privacy Policy

© Copyright 2012 - 2024 | Aspen Power Catamarans

(360) 668-4347 EMAIL US

• PERFORMANCE TOPICS

Optimising Hull Lines for Performance

This article was inspired by a question about the rocker line in the new 8.5m cat Design 256 and I want to stick to the point, so we won’t turn it into a book, but I’ll discuss two issues, hull fineness ratio and some aspects of the rocker profile.

When you manipulate the hull form you’re adjusting the lines in three planes, waterplanes (plan view), buttocks (side view including the keel rocker) and the section shapes. So you need to be aware of how the shapes are changing in the other two planes as you manipulate any one of these three, or all three globally as is now possible with computer modelling.

There are two fundamental constants that you start with and don’t change throughout the process. The big one is the displacement or the amount of buoyancy you need.

If you make the hull finer by narrowing the waterlines you have to increase the draft or make the ends fuller to get back to the required displacement number.

If you flatten the rocker line you have to increase the hull width, fill out the ends, or square up the section shapes rather than having a V or rounded V. 

The other constant is the longitudinal centre of buoyancy. You really can’t do any meaningful shaping of the hull form until you have settled on the these two constants.

A third number that we can plug in as a constant if we want to is the prismatic coefficient which describes bow much volume there is end the ends relative to the cross section shape in the middle of the boat, but in sailing boats this is of less importance compared to other factors. 

The hull lines for Design 256, 8.5m Cat. It's that hump in the rocker line - right under the back of the cabin that brought up the question and is one of the key points discussed here.

Hull fineness.

Fine hulls are fast, but only in the higher speed range. There’s a misconception I come across quite a bit that you can add weight and windage and you’ll still be fast as long as your hulls are fine.

Well you won’t be. Your boat will simply sink to find the new state of equilibrium. If your transoms are submerged you’ll have more drag. If your bridge deck is too close to the water you’ll have slamming. Much better to be conservative with your displacement figure in the design stage than overly optimistic.

And fine hulls have more wetted area so you have more drag in light air where friction resistance is the primary drag factor. 

I’ve seen promotional material for catamarans stating that the boat has less wetted area because it has fine hulls. For a given displacement the minimum wetted area is described by a sphere (or a semi sphere in the case of a floating object). The more you stretch it out in length, keeping the displacement constant, the more wetted area you have.

The more you make the section shape into a deep V or a broad U with tight corners, as opposed to a semicircle, the more wetted area you have. Add into the equation finer hulls are slower to tack.

So fine hulls are only an advantage if your boat is light and has enough sail area to ensure you’re travelling at speeds where form resistance is greater than skin resistance.

In my view the advantage of fine hulls is often overrated as it applies to cruising cats.

At the other end of the scale the resistance curve is fairly flat up to about 1:9 which is still quite fast in most conditions. From there the resistance rises steeply as the hull gets fatter and at 1:8 and fatter you’re suffering from some serious form drag.

This is the rocker line isolated from the lines plan above (in blue) and and the red line shows a more moderate rocker line that achieves the same buoyancy and maintains the centre of buoyancy in the same position.  The bow is to the right.

In the image lower right I've squashed it up and increased the height to make the difference in the lines more obvious.

The difference in the two lines is quite subtle, but races are often won or lost by seconds.

Rocker Profile

So if we’re looking for low wetted area we would want a rocker profile that was even and rounded, relatively deep in the middle and rising smoothly to the surface at each end. But this would give us a low prismatic which is not ideal in the higher speed range, and it’s not ideal for pitch damping which in my view is the critical design factor that is often underrated. 

Pitching is slow. It destroys the airflow in your sails and the flow around the hulls, and your performance is suffering from slamming loads.

The single most effective way to counter pitching is with asymmetry in the water planes. You can achieve that in the with a fine bow and broad transom. Or you can achieve it with V sections forward and a flattened U shape aft. Or you can achieve it in the profile view with a very straight run forward and a bump in the aft sections. A flatter rocker line is better for resisting pitching than an evenly curved one with deeper draft in the middle.

The final result is a combination of all three of these factors.

On a cat like Design 256 the weight is concentrated well aft so we need to get buoyancy well aft.

The kink you see in the rocker profile helps to do this. It also helps to keep the rocker straight for most of its length and smooth the water flow exiting the hull aft at higher speeds, possibly promoting some planing effect.

If we had a more even rocker line we would slightly reduce the wetted area, but we would increase the pitching and the water would exit the hull aft at a steeper angle, increasing form drag in the higher speed range.

How much of a bump can you put in there without creating a flow separation, and how damaging would that flow separation be? I really don’t know. The way all of these factors interplay in the various conditions we sail in is very complex.

Ultimately a lot of this work is gut feel nurtured by experience, observing things in nature and most importantly experimenting and trying new ideas.

Is the new Groupama AC45 a breakthrough that will influence the form of racing catamarans into the future? I don’t think anyone has a computer that can answer that. We have to wait and see.

Symmetric and non symmetric water-planes. The blue line with grey fill is the DWL from the design above. As is typical with modern cat hulls the bow is long and fine, the stern is full and rounded. This is the asymmetry that has a damping effect on pitching. The red line on the other hand is more like you would see on a double ended monohull and quite a few multihulls have also used this shape in the past. It's quite symmetric about the pitch axis and does not have good pitch resistance.

The hull lines of the new 8.5m Sports Cat Design 256

Mad Max , Previously Carbon Copy . She was designed in 1997 but she's the current (2016) title holder of the Australian Multihull Chamionships (2 successive years) and the fastest inshore racing boat in Australian waters.

Join the Newsletter

• Scroll to top

production Strider 24

plywood Romany 34

lightweight 14ft Zeta mainhull

Strike 15 trimaran at speed

28ft Skoota in British Columbia

10ft 2 sheet ply Duo dinghy

24ft Strider sailing fast

36ft Mirage open deck catamaran

• All Our Designs
• For new visitors
• About Richard Woods
• Useful Articles
• Testimonials
• Plan Updates
• Links to Owners and Suppliers
• Consultancy Service
• Boats for Sale
• Blog and Facebook Posts
• Our Cruising Blog (updated Jan 26th 2020)
• Download Eclipse logbook (300 page pdf)
• Download Newsletters 1992-2002 (pdf)
• Download Year Reviews 2002-14 (pdf)
• Download FAQs (pdf)
• Download Boat Tests (pdf)

Hull Resistance and Hull Shape Comparisons

Introduction

As I've said elsewhere, I only like to design boats that are fun to sail. I also know from personal experience just how much effort is involved in building even the smallest boat. I've found that it is the psychological effort that's particularly hard, especially if you are a home builder building alone in your spare time. I also know that there are other people, like myself, who's keeness to build is not matched by manual dexterity.

So I try to design boats that are straightforward to build. In simple terms, if I can build it then anyone can! To do this I try to keep to simple shapes and use flat panels where ever possible. Flat decks in particular have many advantages. For a start they are easier to walk on, while coming alongside and boarding from a marina pontoon or dinghy is a lot safer. Flat panel hulls may not offer ultimate speed, but to be honest, few cruising sailors need the fastest boat while I've found that most people don't have either the skill or daring to sail a racing boat to its full potential.

You have to remember that a cruising boat, especially, isn't just for sailing. It has to be a practical floating cottage as well. And the design of that often over rules otherwise desirable sailing features. And also remember that boats have to be usable in harbours and marinas. It's not like the "good old days" when Slocum and even the Pardey's first went to sea - with no engines and few marinas or even cruisers. So all cruising boats MUST maneuver reliably under power and be easy to board from both the dock and from a dinghy.

That is one reason why I don't now like canoe sterns. They make boarding so much harder than a boat with transom steps (the acid test I always use - "could my mother get on board?"). Safe maneuvering in a small harbour is another reason I like small boats. I also find a trimaran much harder to handle than a catamaran when coming alongside, as it is so difficult to reach the outrigger bows to fend off, especially when compared to the big wide decks of a catamaran. Successful designs are ones that work in every situation, not just those that sail or motor fast in a straight line.

I always try to visulise what a particular design would be like when sailing to windward at 2am in the rain. Or when reefing. Or of course when drifting downwind on a very hot humid day.

I tend to own a fleet of multihulls. Sometimes I just go for a day sail, sometimes I race for the weekend, and most years I spend a long time living on board (I spent every Christmas living on board a boat from 2001 - 2009). All this experience means that I have personally faced nearly every situation you can meet when sailing and I use that experience in my designs.

Hull Shapes and Performance

In this article I will talk solely about hull shapes in relation to performance. Comfort, seakindliness and load carrying are also major factors affecting hull shapes and will be discussed in more detail in future articles.

People try to simplify hull design and performance predictions, formulae like the Bruce Number and KSP spring to mind. These coefficients rely only on basic sail area, displacement and length dimensions yet purport to give an accurate indicator of performance. It's easy to show that these formulae cannot be relied on if you consider that a Tornado would have the same rating whether it was sailing forwards or backwards! I suspect the latter is slower! Its probably as accurate as predicting car speed from the kerbside weight and engine horsepower. In fact hull design is a hugely complex subject while different sailing conditions require different solutions. For example, inshore boats can have a flatter rocker while offshore cruisers should be more veed forward to prevent pounding when sailing to windward in waves.

Some factors affecting yacht design are based on scientific principles and are unalterable, so always apply, whatever ones basic design philosophy and regardless of cross section shape (ie whether one uses a Deep V or round bilge hull for example). Everything else is just styling or dressing up the same proven concepts in a slightly different way. As with all moving objects, speed is the result of the combination of resistance to movement (drag) and available power. In sailing boats the power is related to the sail area while in simple terms drag comes in two forms - friction drag and wave making drag.

Frictional drag is primarily dependent on the Wetted Surface Area (WSA). Less is always better than more and WSA is the biggest factor affecting lightwind speed. The minimum WSA for a given displacement (or boat weight) is the hemisphere (eg half an orange). A longer, thinner hull has proportionately more WSA and so in light winds suffers from more drag and thus is slower but conversely is significantly faster as the wind gets up. In fact this is one reason why monohulls - which are much more orange like, do well in light winds. Spray also adds to wetted surface, one reason why powerboats have spray rails. Lots of spray makes a boat look as though it is sailing fast, but it is actually very inefficient. As an example, because of their heel and deeply immersed lee outrigger, trimarans make a lot more spray than catamarans. But we usually find that they are actually slower, particularly reaching, than an upright, low spray producing catamaran. Round bilge hulls have the lowest WSA and deep V hulls the most.

Many people think that, because multihulls have relatively thin hulls, wave making drag is non-existent, but in fact, nothing could be further from the truth. The size of waves that a hull makes depends on several factors. The Slenderness Ratio (SLR) or Displacement Length Ratio (DLR) is a measure of the fineness of a hull and is the technically correct coefficient that naval architects use. However, it is easier to visualise the hull waterline length/hull WL Beam ratio (LWL/BWL), so that is more commonly used. That's acceptable, as for a given cross-section shape, the SLR is directly related to LWL/BWL. Higher ratios result in smaller waves. Typically the LWL/BWL ratio will vary from 10:1 for a good cruising boat to 16:1 for a racing boat. (Team Philips has a LWL/BWL ratio of 35:1!) Finer hulls are more efficient at high speeds, but as we've just seen suffer from more WSA and so for normal cruising catamarans in average conditions a ratio of 11:1 - 13:1 seems optimum.

The Prismatic Coefficient (Cp) is a measure of the fullness of the ends of a boat, the higher the number the fatter the ends and - surprisingly - the more efficient at high speeds. Intuitively you'd think that a diamond shape would cut through the water best, but that's not actually the case. A high Cp also has the advantage of reducing pitching. But to complicate matters, the lower the SLR the lower the Cp can be. Typically a monohull has a figure around .56, while a properly designed multihull will be about .63. Although such a shape is slower than a lower Cp in light winds that is not a problem as one then has the sail carrying power to add extra sail to compensate. It is when sailing fast in strong winds that you need an efficient hull because you then don't have the stability to carry more sail. As an example a 30' boat with a Cp of .63 will be 1/2 knot faster than one with a Cp of .55 when sailing in 25 knot winds for EXACTLY the same sail area (and crew effort etc). Boats with a low Cp try to race faster by keeping too much sail up and it was these types that often used to capsize 25 years ago. Add in the fact that the high Cp boat won't pitch as much and its clear which is going to be the better boat.

In simple terms the Half Angle of Entry is the angle that the waterlines make to the hull CL at the bow. If it is too low then the boat is wet to sail, and, in extremis, if it is hollow there is a pressure build up further aft which slows the boat. If too fat it is also wet to sail as the bow wave goes vertically up the sides of the boat. All sailors, no matter how skillful, sail slower if they can't see where they are going because they are being blinded by spray! In both cases the correct Cp has to be maintained. So a 10 degree angle seems a good compromise. Vertical bows look fast but its actually very difficult to draw a vertical bow on a hull with both the correct Cp and one that has good reserve buoyancy. Read my articles about the Cape to Rio race to discover what I learnt first hand about the perils of vertical bows!

When I was a design student I took the opportunity to do some tank testing on catamaran models and I investigated the drag from the wave interference between the hulls. I found that this interference caused significant drag at certain speeds - in fact up to 20% when compared to hulls at an infinite spacing. So it's vital to reduce this interference as much as possible. The simplest way is to have a hull spacing wide enough so that the bow waves meet at the stern rather than under the boat. This has the added bonus that there is significantly less bridge deck slamming. In the past designers said that the optimum L/B ratio was 2:1. (In fact they were talking about overall length and beam when obviously it is waterline length and beam that are the crucial measurements.) The reasons given for this ratio were the theories that wider boats would break up and be hard to tack. In practice I've heard that limiting beam had more to do with the width of the boatyard doors! Our Strider Turbo has a LWL of 6.6m and a hull centreline spacing of 4.2m yet I've always thought it was a better sailing boat than the standard Strider. So the general trend is to go as wide as one can. But structural strength is still a problem, even with modern techniques and materials. Wide boats are heavier than narrow ones and that ultimately limits the LWL/BWL ratio to about 2:1 on cruising boats with full bridgedeck cabins.

Turning now to the hull above the waterline, vertical topsides reduce space inside dramatically and in addition are not good news when sailing offshore. As a boat moves in waves so it heaves up and down, causing discomfort and slowing the boat. Flared topsides help counteract this heaving because as the boat sinks the buoyancy picks up more quickly than with vertical topsides. The result is a smoother ride and as a bonus, better load carrying ability for, by the same token, the hull sinks slower so there is less increase in WSA and wavemaking as the boat is loaded. Clearly, freeboard adds to windage and slows the boat. Traditionally yachts had low freeboard because they were large (J Class etc) so people could fit in the accommodation easily regardless of freeboard and it's easy to make a low freeboard yacht look elegant. More importantly, it was hard to make a conventionally caulked and planked boat strong and watertight if it had too many planks (ie too much freeboard). As boats got smaller and as grp took over freeboards had to, and could, increase. Adding a few centimetres (inches) of freeboard adds enormously to interior space and at the same time results in a boat that is drier and more comfortable to sail. Fortunately, in practice I have never found that high freeboard slows the boat down appreciably and certainly not by enough to worry any except the most ardent racer.

Load carrying considerations are an important factor for cruising boats. In general it's natural for people to add weight aft because it is easier to load stores near the companionway than forward. Engines and their associated tanks, generators, a/c units etc are also always aft. So I always try to add extra buoyancy near the stern. That means that when empty the boat will probably float stern up. Too many poorly designed multihulls float stern down and drag their transoms.

Pros and Cons of popular hull shapes

The deep V is a simple to build hull shape that matches the human body as it is narrow low down and wider high up so it is a good choice if the accommodation is only in the hulls. It can make to windward without keels or boards - just - but it's more maneuverable and makes less leeway with them fitted. Deep V hulls pitch more than any other hull shape, particularly if they have canoe sterns. Hull asymmetry is needed to reduce pitching, a canoe stern is obviously as pointed as the bow so it's bound to pitch more. They have more WSA than any other hull shape so are slow in light winds.

The flat bottom hull is also easy to build and has the added advantage that it is self supporting during building and transport. It needs Veeing forward for offshore sailing or it will pound. Then it becomes a hard chine/single chine hull. Carefully drawn such a shape is a close approximation to a round bilge hull, but without any complicated building.

The round bilge hull is the only hull shape that can be varied over it's length so one get exactly the shape one wants. It has minimum WSA, and so is also the optimum hull shape but it is the slowest to build. A topsides knuckle helps deflect spray, adds interior volume and makes it easy to join flat topsides to the curved bottom. It also makes a nice styling line.

From the start of my design career I have always tried to design balanced, undistorted hulls that sail easily on all points but are not too extreme. However, I have made a few changes to my hull shapes over the years. First I have increased freeboard (in common with most designers, monohull and multihull). I have also increased the centreline spacing and where appropriate, drawn a bigger knuckle. I haven't designed any deep V boats for a long time because of the pitching and light wind speed problems. I have found the flat bottomed or single chine hulls are as simple to build and are more efficient hull shapes.

Finally, I am one of the few designers who use all feasible hull shapes and so can choose the most appropriate one for the intended use. I'm not committed by dogma to any one hull design. The performance differences between different hulls are easy to see, however I have not noticed any practical difference in seaworthiness between them.

The following sketches are typical hull cross sections. Please note, these are not to scale and are not real boats, instead they are just examples of the different hullshapes we use in our designs. (For those not familiar with lines plans: Only half sections are shown. The forward half of the boat is shown to the right, the aft half is to the left of the vertical centreline.)

This is the "Dory" hull used on the Janus and Gypsy as well as the Strike trimaran mainhulls. Note that the Janus does not have a V'eed area forward (as shown) as the bottom is narrow enough to prevent slamming on such a small boat.

This chined hull is used on Flica, Mirage and Romany and is a close approximation to a round bilge hull, but built in flat panels

This is a deep V hull used on Surfsong, Windsong and Mira (deep V version)

This is the chined V hull used on Meander, Rhea and Ondina. If these larger boats had a conventional V hull then either the gunwale or keel panel would have to be very wide so that the hull had the correct displacement. By adding a soft chine the lower hull section can be well flared, while the topsides remain nearer vertical. This hull shape has the added advantage that the hull panel is stiffer and, as each section is smaller, it can be easier to make.

This continuously curving hull shape is used on Wizard, Sango and Wizzer. It has a similar below-waterline shape to a Strider hull (for example) but the bulge in the topsides allows a vertical bow to be drawn while keeping a good flare forward to prevent nosediving. It also adds to the interior room, especially at shoulder level. These hulls can be built in strip planking or foam sandwich but it is harder to build than the small knuckle hull shape.

This "Small Knuckle" round bilge hull is used on Strider, Shadow, Merlin, Gwahir, Skua, Gypsy (round bilge version), Mira (round bilge version), Scylla, Nimbus, Rhea (round bilge version) and Cirrus. This shape is easier to make than the one below. The knuckle is small and is usually made from solid timber (eg 2" x 1"). Even so it has proven effective at reducing spray and slamming. The hull bottom can be double diagonal plywood or strip plank. The topsides of both this hull shape and the one below can be strip plank or sheet plywood. Alternatively both knuckle designs can be built in foam sandwich with a flat panel topside panel.

This is the "Large Knuckle" hull used on the Scorpio, Javelin, Sagitta, Eclipse and Transit. It is the most sophisticated shape I draw, and takes the longest to build. The large flare increases space inside and cuts down on spray. The angle of the hull at the WL is actually higher than on other hull shapes. That means that it sinks relatively slowly as you add weight. A big advantage for cruisers. But it also means the boat doesn't pitch and heave so much, ie vertical movements are reduced. That is because it is (slightly) harder to make the boat sink as it goes through waves. All minor differences but they add up if you are looking for the best all round shape.

Having said that, if you are planning on using LAR keels rather than daggerboards then you will probably be better off with a flat panel hull. There is no point in taking just one part of the overall design to the limit, you have to balance the trade off for the whole boat. So don't fit daggerboards and cheap sails! Makes no sense to me.

James Wharram Designs

Search Our Site

• Self Build Boats
• Professionally Built Boats
• Choosing a Boat
• How We Design
• Photo Gallery
• Video Gallery
• Articles & Blogs
• Wharram World

Catamaran Stability

Foreword (james wharram, 2004).

It is 50 years since I designed my (and Britain's) first offshore Sailing Catamaran. The accepted opinion at the time, expressed in Yacht Magazines, was that the offshore catamaran would break up in high sea waves, that their motion on the high seas would be so violent as to render the crew helpless and that the double canoe/catamaran could not sail to windward.

Well, the voyage of Eric de Bisschop of France who sailed his 38ft. KAIMILOA half way around the world in 1937/39 and his two by him inspired 'Sailing Sons', Rudy Choy of Hawaii in the Pacific and James Wharram in the Atlantic proved these 'theorists' wrong.

What is interesting on looking back is that no critic at the time mentioned 'capsizing' as a possible fate of the historic offshore double canoe/catamaran. The reason is that early in the 1950s, the wartime experience of hundreds of men who had survived, sometimes for weeks, in small open boats, in rubber life rafts, cork Carley rafts or even floating wooden hatch covers, encountering severe storms with big waves without capsizing, was in seafaring circles common knowledge.

That you could capsize at sea on a form stable sailing ship (which is what a catamaran is) through having too high a mast and too much sail area was at the time also common knowledge amongst seamen, as it affected all commercial sailing ship design. There were many people around in the 1950s who still had knowledge and practical experience of such ships. Their knowledge certainly influenced the mast heights and sail areas of my first seagoing catamaran designs, as did the writings on Form Stable ships by Howard Chapelle, the great American naval architect.

In the late 1950s, the Prout Brothers were developing a 16ft. racing day boat catamaran. It was fast and outsailed all monohull racing, dinghies of the time. Like racing sailing dinghies, without skilled handling, they capsized frequently. Still, with the attendance of the patrolling Race Guard Boats no one died.

Offshore catamarans began to first develop in the 1960s. From the beginning, there were some designers, like myself, who saw them as Form Stable boats following traditional Form Stable Stability values i.e. boats which 'looked after their crew'.

There were also designers (not many), drunk on the speeds of day racing catamarans, who used the sail areas, mast heights and stability values of the day racing catamarans on Offshore Cruising Catamarans, i.e. at all times the Crew looked after the stability of the boat.

Unfortunately, designers of these low stability catamarans have nearly always tended to imply in yacht magazines, to the public, that they are more skilled designers "Because their boats sail faster"?

Equally unfortunate was that by 1976 many of these low stability catamarans were publicly capsizing, when their trained crew got tired or, particularly, when sold to unsuspecting monohull sailors. Suggestions in England and America were made to 'ban offshore multihulls'. Hanneke Boon and I wrote our first article on cruising catamaran stability ("The Stable Multihull") in 1977, and things settled down again.

However, around the late 1980s another group of young designers from racing background or using racing catamaran concepts moved into Cruising Catamaran design and, once again, capsizes with deaths occurred. So, again we wrote in another article on our observations on safe stability for Cruising Catamarans.

This article was first published in 'Practical Boat Owner' (UK) in August 1991 and since then in several other countries. The I.S.O. has recently also published formulas for calculating catamaran stability as part of the Recreational Craft Directive. On examination, their formula is the same as the one published by us in 1991 with a slightly smaller safety margin for Dynamic Stability (70% to our 60%). So far, the I.S.O. has not yet given recommendations as to what is a 'safe' stability for offshore sailing.

Introduction

In November 1989, the British Multihull Club, M.O.C.R.A., had an International Symposium on multihull design to celebrate its 20th anniversary.

During the lunch break, one very pregnant lady asked me: "Why don't they discuss capsizing? That is what I want to know about. I do not like heeling monohulls, but I do not fancy swimming with my baby out of an upside down catamaran."

Unfortunately, what I had to tell the pregnant lady is that they never seriously discuss capsizes at Multihull Symposia except in a self-congratulatory way, saying that an "upside-down catamaran floats as against a monohull that sinks". Ignored are hypothermia, broken limbs, lost crewmembers and mothers frantically trying to find their children to say nothing of at least half the value of the boat, i.e. the interior destroyed by the inrushing water.

It is a very emotive subject between designers and their followers because it touches not just on sales and profits, but also on masculine subjective attitudes like high tech., low tech., modern, traditional, taking risks, being cautious...etc. Symposium organizers realize that free discussion would lead to uproar. For the monohull sailor wishing to buy a cruising catamaran to suit his/her family's needs, Multihull Symposia and Multihull Magazines so far have given no real information.

Fortunately, the formulas that most catamaran designers use nowadays to calculate stability are not all that difficult to understand, and with them a prospective owner with a little background knowledge on sailing ships in general, can make his/her own decision as to whether the cruising catamaran they desire has the stability to be safe for their intended usage.

If you have forgotten most of your mathematics since you left school and, like most of us, hate to admit it, do not be frightened of the word formula. Calculators now do most of the work, and everyone knows or has some bright adolescent only too eager to use and demonstrate his/her latest calculator acquisition. However, the calculator only produces figures. To relate these to our needs, we do need to know some sailing ship history.

Polynesian Origins

The historic catamaran is the workboat of the Polynesian Pacific. Archaeological excavations, legend and early Western observers have shown that they had been in use hundreds of years - perhaps thousands - for fishing, coastal trade and ocean exploration, a background usage similar to that of the Chinese junk types and our own traditional Western sailing boats (before the development of the modern ballast keel yachts). Catamarans have exactly the same stability behavior as Junks and the traditional Western Sailboat.

Joshua Slocum's SPRAY is a typical example of a workboat of the late 18th and early 19th century. (See Fig.1)

What kept the SPRAY and traditional sailing ships from capsizing under the pressure of the wind on the beam were the wide hull beam, flattish bottom shape (i.e. "form stability"), and a selection of heavy rocks (i.e. "ballast stability"). In addition, the masts were kept short to lower the heeling moment of the sails.

Extra sail area for light winds was achieved by spreading the base of the sails out by means of bowsprits and bumpkins rather than raising the sails higher on a longer mast, creating a greater heeling/capsizing force.

According to Chapelle, in his book "The Search for Speed under Sail", if traditional sailing ships heeled much more than 55º, then they were in trouble. The loose rock ballast, about 10% of the total displacement, could break loose. A complete capsize would then occur and the boat would remain upside down. Capsizing, until the advent of the modern ballast keel yacht, was the theoretical possibility of ALL seagoing sailing vessels. Designers/ Boatbuilders have been able to design boats stable enough to stay well away from the possibility of capsizing for at least 3000 years. (ULU BURUN SHIP -Nat. Geographic Magazine, Dec. 87)

Racing developed the modern ballast keel yacht. To sail closer to the wind the rigs got higher. To balance that, the ballast changed from rocks to heavy iron (this became cheaper with industrialization), and finally, to be able to use even higher masts, the ballast changed to the heavier lead and moved from inside the hull to the outside in a deeper keel. As a side result, and not intended by design, the modern self-righting yacht was born.

Those who observed this development towards self-righting yachts did not regard it as a total blessing. They commented on how these "new" yachts plunged and rolled, which made sailing very uncomfortable and caused seasickness.

Even so the modern ballast keel yacht is still a relatively broad-beamed vessel, i.e. with a waterline length about 3 times longer than its beam - in technical terms, a length/beam ratio of 3:1.

Beamy hulls of 3:1 have to push a lot of water around them when sailing. This produces the well-known drag waves. (See Fig.1) and limits the maximum possible speed to approx. 1.4 x √WLL (in feet). Thus with a waterline length of 25 feet, your average speed will be about 5 - 6 knots.

The catamaran's unique speed potential, greater than that of the equivalent size monohull has arisen because it developed out of two ancestral boat types of the Pacific. Around the Pacific Ocean of antiquity there were various maritime peoples. Some used large paddling canoes up to 60 feet long for coastal trading, fishing, and whale hunting. (See Fig.2) Their long slim hulls with length/beam ratios of 12:1 to 20:1 allowed the water to part and run around them without creating drag waves at √WLL. They could reach speeds as high as 2 or 3 times the √WLL. So a canoe of 25 foot waterline length could reach speeds of 10 knots and over.

Hard paddling men with their food and water add up to weight. Even the toughest men can only paddle for a few hours.

Other Pacific maritime people had sailing rafts. Thor Heyerdahl's Kon Tiki expedition of 1947 used a modern replica of this type of craft. 45 ft. long, 18 ft. wide, rigged with a squaresail, manoeuvred by daggerboards, it could sail sufficiently against the wind to be a true sailing craft. It carried a crew of six in basic, though surprising comfort across the Pacific. (See Fig.2b)

It was not a speedy craft, but by its beam and weight, it was practically impossible to capsize and thus had stability, an essential part of seaworthiness.

Long ago some genius in the Pacific joined two fast, easily driven canoe hulls into a beamy raft shape, giving a new type of sailing craft with the stability of the broad beam raft and the high-through-the-water speed potential of the single canoe. (See Fig.2c)

Fig.2c is an approximation of a traditional Polynesian sailing craft and how it developed from its two ancestral types. It has a raft-like deck platform that could house people, and ample room to move around. From early European explorers' descriptions, the crew sailed with families, friends, lovers, singers and dancers in one joyous group from island to island - a marvellous way of life.

Efficient Crab Claws

Modern wind tunnel tests, as done by Tony Marchaj, of Southampton University, have shown that the Polynesian sail shapes were highly efficient to windward. With efficient sails, a hull form that allowed the boats to sail faster than the maximum speed of 1.4 x √WLL of Western ships and enough raft stability to be uncapsizable, (i.e. the sails would rip before the ships could capsize), the Polynesian catamaran was a remarkable sailing craft and worthy of being developed as a modern pleasure sailing craft.

Though to-day's yachtsman increasingly accepts the concept of the double-hulled ship, he/she places modern urban attitudes on the catamaran. These are: 1) to get the maximum speed potential out of the catamaran form. (Faster is always equated with being better, no matter what the cost.) 2) to alter the hull form to get as close to modern urban style accommodation needs as possible, which was described in the recent RYA (Royal Yachting Association) 'Competent Crew Handbook': "The typical modern cruising yacht has....interior design principles....much in common with a caravan".

The quest for speed

It is Demand 1) which creates most controversy for, in order to reach the maximum speed potential of a catamaran, you have to carry a large sail area, which reduces its inherent stability to the point, where with the average cruising crew, it is in danger of capsizing well before the average monohull suffers a knockdown.

With a sense of realism any would-be catamaran owner, once he/she knows how to calculate stability, can make his/her own decision when viewing a cruising catamaran design, whether they want maximum speed or maximum stability. As the formula will show, you cannot have both at the same time. Fig.3 shows how to calculate catamaran stability. Fig.4 and Fig.5 are helpful to learn how to determine the position of the center of Effort and the Center of Lateral Resistance.

In 1976, catamarans built using this stability formula were capsizing all over the world at mean wind speeds a lot lower than the wind speed the formula predicted.

In an Article called "The Stable Multihull", published in 1977, Hanneke Boon and I demonstrated that the given formula was a static formula for static state conditions.

However, wind is a turbulent, gusty, dynamic force. Gusts can be as much as 40% to 60% greater than the mean wind speed, so the static formula has to have built in a safety factor for dynamic, natural state wind conditions to allow sailing craft to absorb the extra wind gusts without immediately capsizing in the manner of a dinghy.

Since 1977, this dynamic formula concept, after much initial argument, has been accepted. It has now been generally agreed amongst designers, that taking 60% (x 0.6) of the Static stability allows for a suitable safety factor. So, the Dynamic Stability (i.e. maximum mean wind speed it is safe to sail in before reducing sail) is found as follows:

At the M.O.C.R.A. symposium were the designers of two 34-35 ft. catamarans about to be placed on the market. We will use them as examples of two opposing design attitudes towards speed and catamaran stability. Their dimensions, obtained from yacht magazines and brochures, are given in Fig.6a .

The first noticeable points from Fig.6a are that catamaran B has a wider beam than catamaran A, but carries 33% more sail and has a much lighter construction weight.

If you asked the opinion of the designer of catamaran A with reference to design B, he would say that he has been designing and building catamarans for thirty years, that his sail area to weight ratio to beam etc. had evolved to provide the maximum stability, Which adds up to sailing safety.

The designer of catamaran B, a more recent designer in the cruising catamaran field, would point out, that his design had much more beam (which is a feature of catamaran design over the last ten years) and. thus has the stability to carry the extra sail area.

You, the would-be catamaran purchaser, without the aid of the given formula would be at a loss to know:

• The Static Stability of either design, which can be described as the "Moment of Truth" when the boat is on the edge of capsizing i.e. when the windward hull lifts out of the water.
• The Dynamic Stability , when it is safe to sail along with all sails up and have sufficient reserve stability to meet safely any wind gusts that lie under that lovely white cloud or just along the coast where a narrow, scenic valley opens to the sea and down which the wind unexpectedly gusts.

Fig.6b shows the working out of the Static and Dynamic stability of both designs, using their lightly loaded weights, sometimes described as racing trim. From the formula we can see that catamaran B has less stability in spite of its wider beam than catamaran A. So what!

These figures must be related to the real world of sailing. To do this I will use a book by the sailing meteorologist, Alan Watts, called "Instant Weather Forecasting" (published by Adlard Coles).

On pages 10 and 11, Alan Watts describes the behavior of dinghies and deep keel monohulls in various wind strengths. (I have extracted these details for wind forces 3 to 6.). See Fig.7 .

Catamaran A with a Dynamic stability of 18.2 knots ( Fig.6 ) needs to be carefully sailed or reefed by the middle of force 5 (remember this is a lightly loaded catamaran). Alan Watts describes the deep keel monohull in a force 5 wind as "Craft's way somewhat impeded by seaway. Genoas near their limit. Yachts approach maximum speed.'

Force 5 is a well-known wind state that to the average yachtsman draws attention to itself by strong audiovisual signals of waves and wind, which leads him naturally to take particular care in sailing, changing headsails or reefing.

Therefore, if a monohull yachtsman handling Catamaran A is slow at reefing in force 5 and is hit by a strong wind gust, he would have approx. a 60% stability safety margin to absorb his slowness and the gust, for his windward hull would not begin to lift from the water (the Moment of Truth) until 30.5 knots of wind hits the sails (i.e. a force 7 gust).

Similar sail handling

Conclusion, the same sail handling habits of the monohull cruising sailor can easily be applied to the lightly loaded catamaran A, without fear of immediate capsize. Catamaran B with a Dynamic stability of 13.3 knots (lightly loaded) will need to be carefully handled, aware of wind gusts, or reefed, to preserve its 60% stability safety margin in the middle of force 4 (11-16 knots). THIS IS AT ONE FORCE lower than monohulls or Catamaran A.

Watts describes force 4 for monohulls as: "Best general working breeze for all craft, genoas at optimum". With the necessity to reef to preserve the 60% safety margin, this description does not apply to Catamaran B. However, his description of force 4 for dinghies does, for he writes: "Dinghy crews lie out...", i.e. are attentive to stability to prevent capsizing. As dinghies, so Catamaran B.

Catamaran B continues to echo dinghy-handling characteristics at increasing wind strengths. Catamaran B's Static stability, i.e. hull lifting point, lies on the borderline between force 5 and 6 (22.5 knots). Watts' dinghy handling descriptions for force 5 and 6 are as follows: Force 5: "Dinghies ease sheets in gusts...some capsizes." Force 6: "Dinghies overpowered when carrying full sail. Many capsizes." Conclusion: Lightly loaded Catamaran B, above wind force 4 can only be sailed safely by skilled dinghy type sailing techniques or should be reefed at force 4.

Why not reef?

The enthusiasts for the Catamaran B type argue that for general family cruising, you can reef Catamaran B and give it the same monohull type stability as Catamaran A. At other times, with a trained crew and all sails up, you have the benefits of fast exciting sailing.

This is true, and Fig.8 shows the use of the formula to see how much sail you would have to reef down to give Catamaran B the same stability as Catamaran A with all sail up. This is a sail reduction from 750 sq.ft, to 511 sq.ft.

Providing that reefing was a rigidly applied rule when there was not a fully experienced dinghy technique skipper standing by the sheets or helm, it would be effective.

If you feel a little conspicuous, sailing reefed in a Force 4 breeze, you can carry more load to stabilize Catamaran B. Again, the formula (see Fig.9 ) shows that if the boat weight is increased to 11787 lbs with extra stores and equipment (in fact, its full cruising payload), your stability would again equal that of Catamaran A in its lightly loaded condition.

However, if Catamaran A increases its payload to the designed maximum (approx. 11050 lbs) its Dynamic stability goes up too, and it would require a gale gust of 34 knots, to lift one hull out of the water. This conforms to the wind stabilities of traditional sailing craft throughout the ages. A cruising catamaran designed to these principles gives no stability problems to the average yachtsman and his family, enjoying its broad decked upright sailing.

• Subscribe Now
• Digital Editions

DutchCat: The 15p-per-mile-marvel motor catamaran

• Electric boats

This electric or hybrid-engined motorcat takes fuel-efficiency cruising to a new level

Evolution rather than revolution is the name of the established boatbuilder’s game. The finish and layout of current models might be a quantum leap ahead of where they were a decade ago, but conceptually little has changed. Even new ideas such as Azimut’s Magellano range with its ‘dual-mode’ hull capable of running comfortably at displacement and semi-displacement speeds, offer only tiny gains in fuel efficiency. But with ever more emphasis on environmental concerns, pressure for change is growing in a motor boat world where 1mpg for a 40ft planing boat is the norm. Enter Jan van Eck, the man behind the DutchCat. Rather than wait for the mainstream builders to rip up the rule book, he has simply started without one and created what he believes to be the true future of motorboating.

His vision starts with the hull shape. It was seeing catamaran sailing dinghies consistently outperform monohulled ones that convinced Jan twin hulls were more easily driven. Of course, motorcats are nothing new but most existing powercats are far wider than monohulls of a similar length, making them unwieldy for inland use. The Fountaine-Pajot 44, for example, has a beam of 6.6m, compared with the monohulled Azimut Magellano 43 at 4.4m. The 41ft DutchCat comes in at 4.9m, far closer to monohull territory and crucially granting it access to the French canal system, where locks are typically just 5.2m wide.

One boat, two versions

Designed by Vripack and RCD Category B-rated, there are two versions of the DutchCat hull. The ‘Comfort’ version has a round bilge form and long shallow keels, similar to a sailing yacht, and is designed to run at lower speedswith smaller engines. The ‘Sport’ hull is a more traditional powerboat form with sprayrails and tunnelled props for higher speeds, toppingout at 22 knots with bigger motors. Crucial though hull design is, it’s only one part of DutchCat’s energy efficiency equation. Similar blue-sky thinking has been brought to bear on pushing that ultra efficient hull shape through the water. Perhaps the most radical power source is an all-electric setup that uses twin Kräutler 48V 10kW (14hp) or 15kW (21hp) motors connected to conventional shaftdrives for a maximum speed of 8.5 knots and a cruising gait of 4 to 6 knots. Gel traction 48kWh batteries are standard, with Lithium ones an option. DutchCat claims about seven hours of cruising at 5 knots and about ten hours to recharge from a 16A supply. Pure diesel is an alternative. Comfort-spec boats rely on a pair of Yanmar 3YM30 3-cylinder 29hp engines to yield about 11 knots flat out and cruise at 8 knots. Opting for the Sport hull configuration allows twin Yanmar 4BY3 150hp engines to boost maximum velocity toward 22 knots.

Recommended videos for you

Out on the water

We had the chance to try the diesel hybrid setup with twin 29hp Yanmars. Two hulls mean two bow thrusters – a pair of 55Kgf Vetus units combine with wide-spaced shafts to make wriggling out of Amsterdam Marina and on to the IJ fairly painless. Despite being the first boat from this new company, it feels well engineered with commendably low noise levels at 2,500rpm which equates to a 7-knot cruise. But to really drop the decibels, switching to all-electric is the way to go. The electric motors use the same engine controls as the diesels, so it’s just a case of switching off the Yanmars, engaging the electric motors and then throttling back up. Under electric power there are two obvious differences. Performance is muted – 5 to 6 knots is as much as you’ll get if you want meaningful range. But so is noise. The closest comparison would be sailing, with the gentle gurgle of water around the hulls the only sound. This speed is more than adequate for inland waterways and should allow for 5.5 hours of cruising from the 38kW battery pack.

Continues below…

Motor boat stabilisers: DMS’s new stabilisation fins

DMS's new flapping fins could become a staple for motor boats

Hybrid heaven: Adler’s 76 Suprema

Taking diesel electric propulsion to a new level, Adler's 76 Suprema may just be too innovative for the yachting marketplace

So how does that efficiency translate to cost? Like any boat, travelling at displacement speeds is the key to the biggest savings – DutchCat hasn’t rewritten the laws of physics. Nonetheless, with the smaller diesel engines, the boat is burning under a gallon an hour at 7 knots, which is less than half that of the slightly longer but narrower hybrid-hulled Magellano 43 (albeit without its 22-knot top end). With marine diesel currently hovering at around £1/litre that’s about £4/hour. At 5 knots under electric power, it’s using roughly 5.5kWh. With 1kWh of mains electric costing 13.5p, that’s about 75p/hour or a miserly 15p per mile!

So is this the future? Well, it’s certainly one of the most credible attempts to create something truly new and efficient that we’ve seen for some time, and it’s telling that it comes from a brand new start-up with zero boatbuilding history.

Hugo’s take

Combining the efficiency of a catamaran hull with the low-running costs of a diesel-electric hybrid makes perfect sense, particularly for inland cruising. I reckon DutchCat are on to something.

At a glance…

Build: GRP RCD: B for 12 people LOA: 41ft 2in (12.55m) Beam: 16ft 1in (4.90m) Draught: 2ft 9in (0.85m) Displacement 12 tonnes Price: from €467,533 ex VAT Contact: DutchCat   

Bluegame BGM75 yacht tour: The €6.8m powercat that thinks its a monohull

Archipelago 40 first look: new hybrid powercat sold by british yard, the world’s biggest electric foiling boat is coming, latest videos, navan s30 & c30 tour: exceptional new axopar rival, galeon 440 fly sea trial: you won’t believe how much they’ve packed in, parker sorrento yacht tour: 50-knot cruiser with a killer aft cabin, yamarin 80 dc tour: a new direction for the nordic day cruiser.

Capilano Maritime Design Ltd.

• Case Studies
• Analysis & Consulting

High-Efficiency Catamaran Design

The contributor.

The National Research Council Canada (NRC) as represented by its Industrial Research Assistance Program (IRAP) funded the research in 2020 and 2021.

The objective of the research project was to develop an adaptable catamaran ship design valid within a certain design space given by the main dimensions (length, draught, beam, displacement, number of passengers and operational range).  The aim is to be able to design variants efficiently, quickly and with high accuracy and thereby limit the technical risk for both the client and Capilano Maritime Design Ltd.

The design platform is intended for various applications such as commuter passenger ferry, harbour cruise, offshore supply, research vessel etc.

The catamaran designs in the range of the following main dimensions were explored:

The initial focus was on small passenger vessels with lengths ranging from approximately 20 to 40 metres.   Specific areas of interest were catamarans with low l/b ratio, low Froude number (low speed to length ratio) and/or high displacement to length ratio.

The main technical risks identified are: resistance, wave making, propulsion and weight.

In order to evaluate a large number of hull form variations a CFD set-up was validated using published hull forms and model tests results of the catamaran Delft 372 as well as a comparison was made to empirical formulas for resistance calculation of catamarans.

The CFD calculation results, empirical formulas and the published model test results for the Delft 372 agreed well for both resistance, dynamic trim and sinkage, as shown in below figure.

This validated set-up was subsequently applied using different hull shapes to determine their hydrodynamic performance.

The hull forms that were part of the design study had a considerable higher displacement than the validation case (Delft 372), in the order of 60%, and therefore also distinctively different hull characteristics. Thanks to the extensive CFD studies we determined the limitations and accuracy of these empirical formulas at or beyond their application range.

In parallel, a structural layout based on DNV-GL’s rules for high speed and light craft (HSLC) rules was prepared and utilized for a FEA analysis to investigate vulnerable spots, accurately determine design margins and optimize material allocation hence minimizing structural weight.

During the course of the research project several design tools were developed that enable CMDL to develop catamaran concept designs in a shorter time frame while increasing the level of detail and confidence, thus reducing the technical risks and consequently reducing design margins earlier.

• Remmlinger, “The resistance of the Delft 372 Hull”, 2014
• Van’t Veer R. “Experimental results of motions and structural loads on the 372 catamaran model in head and oblique waves.” TU Delft Report, N.1130, 1998
• Van’t Veer R. “Experimental results of motions, hydrodynamic coefficients and wave loads on the 372 catamaran model” TUDelft, 1998
• Broglia R, Zaghi S. “Calm water tests for the DELF 372, Catamaran model at several hull separations”, INSEAN, Report, 2010
• Broglia, B. Bouscasse, B. Jacob, A. Olivieri, S. Zaghi and F. Stern, “Calm Water and Seakeeping Investigation for a Fast Catamaran” 11th International Conference on Fast Sea Transportation, FAST 2011, Honolulu, Hawaii, USA, September 2011
• DNVGL-RU-High Speed and Light Crafts- Part 3
• DNVGL-CG-0127- Finite Element Analysis
• Liang Yun, Alan Bliault, Huan Zong Rong, “High Speed Catamarans and Multihulls”, Book
• Liao PK, Quemener Y, Syu YC, Chen KC, & Lee YJ, Validation of Practical Approaches for the Strength Evaluation of High-speed Catamaran under Beam and Quartering Seas, The 31st Asian-Pacific Technical Exchange and Advisory Meeting on Marine Structure, 2017

Category: Analysis & Consulting

Client: National Research Council of Canada

Services Provided: CFD, FEA, Development of Tools for Structural Design, Weight Estimation and Wake Wash

Date Completed: 2021

Location: North Vancouver, BC

To enquire about how we can help with your project, let’s talk. Contact Us

Copyright ©1997-2024 Capilano Maritime Design Limited. All rights reserved. Privacy Policy Terms of Use

• 2024 BOAT BUYERS GUIDE
• Email Newsletters
• Boat of the Year
• 2024 Freshwater Boat and Gear Buyers Guide
• 2024 Boat Buyers Guide
• 2024 Water Sports Boat Buyers Guide
• 2023 Pontoon Boat Buyers Guide
• Cruising Boats
• Pontoon Boats
• Fishing Boats
• Personal Watercraft
• Water Sports
• Boat Walkthroughs
• What To Look For
• Best Marine Electronics & Technology
• Watersports Favorites Spring 2022
• Boating Lab
• Boating Safety

Six Amazing Boat Hull Designs

• By Dean Travis Clarke
• Updated: October 25, 2016

The American boating consumer bears a remarkable psychological profile when it comes to wants and needs.

A cursory glance at the lines of most boats proves that profiles haven’t changed dramatically over the past 60 or so years. Certainly, construction methods such as resin infusion and injection molding have altered business as usual, and ingredients have also changed to include all manner of space-age composites, epoxies, paints, computer mapping for engines that produces vastly greater horsepower from smaller blocks, and so on. Even propulsion has changed with the advent of pod drives and big outboards. But here’s the weird part: Any time a designer or builder introduces a model that looks significantly different, whether it is Euro-styled or functionally clunky, it fails. It doesn’t matter how well the boat performs, the typical boater rejects it because it doesn’t look like what he knows. We, as an enthusiast niche involving boats, are horribly set in our aesthetic ways.

Look at how well multihulls handle heavy seas. When it comes to seakeeping ability, efficiency and performance, the catamaran has a lot going for it, as anyone who happened to catch some of the most recent America’s Cup racing can attest. And yet, to date, production multihulls have enjoyed only moderate acceptance by boaters.

Here are six of the latest hull-design innovations and technologies being used elsewhere in the maritime world that we will likely never accept for our recreational boats — even though they all work well.

Wave-Piercing Hulls Most accounts cite wave-piercing technology as coming on the scene around the start of the 20th century. However, it has been employed as far back as the times of the Phoenicians and ancient Romans. The design concept consists of a bow with little buoyancy, a hull that slopes inward from the waterline and, ergo, a large reduction in wave-making resistance. While it works well in heavy seas, the drawbacks include reduced interior volume forward and a very wet ride because the waves come up and over the bow as a matter of course. Wave piercers fell out of favor for a period of time due to these same drawbacks but have recently enjoyed a resurgence of popularity because of their dramatic fuel-efficiency gains.

Stepped Hulls OK, this hull form has achieved a certain level of acceptance in our recreational boats, mostly in performance boats or offshore center consoles. But why isn’t it more popular? The stepped bottom has been around as a V-bottom refinement since at least 1912. Steps are grooves in the hull stretching outward from the keel to the chines. Most hulls sport one or two steps per side. And a vessel should really be capable of cruising in excess of about 30 knots for a stepped hull to be worthwhile. Steps work by allowing air to be “injected” against the running surface, breaking contact between part of the hull and the water, which in effect turns the running surface into numerous short, wide planes, rather than one long, narrow one.

How much the hull surface contacts the water directly determines the amount of drag a hull suffers. Steps (also called vents) decrease the amount of hull contacting the water (called the wetted surface), thereby decreasing drag, increasing speed for the same horsepower, and increasing fuel efficiency. It all sounds good. But steps also come with potential drawbacks. Though modern deep-V designs have enough deadrise to counteract the problem in most cases, stepped hulls have been known to suffer from transom slide in sharp turns at speed. They also require attention to loading and trim because the steps need the proper angle of attack to function correctly; they don’t offer an advantage in flat, calm water; and they require a special trailer.

Most owners of stepped-hull vessels are experienced and want to travel at high speeds in moderate to heavy seas, and/or achieve good economy and range. Yet to date, performance and center console builders aside, only Regal Boats, with its FasTrac hulls, and Formula have committed to using steps in production cruisers and sport boats.

Asymmetrical Twin Hulls This unique design concept comes from the drawing board of Larry Graf, the pioneer who put power catamarans on the map here in the U.S. when he founded Glacier Bay Boats in 1987. His new company, Aspen Powerboats, employs a cat design where one hull is narrower (35 percent) than the other. His patent calls it a Power Proa, and it relies on a single engine in only the wider of the two hulls. The hull shapes, alignment and placement compensate for the offset propulsion thrust, allowing the vessel to run straight and true. With only one set of running gear in the water, inherent appendage drag is reduced by 20 percent. Combined with the efficiency of the hull designs, overall fuel efficiency of the Aspen rises to an impressive 70 percent over monohulls of comparable size. Aspen won an award for the best 30- to 39-foot catamaran in the world in 2014.

SWATH A quick glance might lead you to believe that a SWATH (small waterplane area twin hull) vessel is a catamaran. And it is but only to the extent that it has two hulls in the water with a bridge across the top. But that’s where the hulls’ similarities end.

Consider a submarine. Once under the surface, it runs stable, with no roll or pitching from wave action. All that wave energy remains on the sea surface. That basically explains how a SWATH design functions.

If you’ve ever dived under a wave at the beach to avoid being smacked by it, you know that the water beneath the wave is calmer. SWATH minimizes a vessel’s volume where the water meets the air (which is where all the wave energy is at its peak). The bulk of the vessel’s displacement and buoyancy runs beneath the waves, affording amazing stability, even in big seas and at high speeds. Please think of high speeds as a relative term here, as this is not a planing hull. What SWATH does provide, however, are a wide, stable deck and unsurpassed ride quality, especially in rough seas.

Drawbacks to SWATH designs include the fact that each hull must be custom designed. Draft runs deeper than standard hulls (especially planing hulls). The underwater “torpedoes” providing buoyancy must run parallel to the water’s surface, which requires a fairly complex trim-control system. And the underside of the deck must be far enough above the sea surface to avoid waves slamming up into it. Finally, SWATH vessels cost more to design and build than conventional hulls.

Hydrofoils Once the strict province of commercial ferries and a few high-speed military vessels, the most recent America’s Cup has spurred hydrofoil acceptance to new heights. Will it catch on with powerboats?

The hydrofoil design acts exactly like an airplane wing, providing more lift than the drag coefficient the vessel produces, thereby lifting the entire hull out of the water. Only the hydrofoils remain in the water, unaffected by surface wave action. In fact, hydrofoils cut inherent resistance to zero while the hull is out of the water. In the case of power-driven boats, you still suffer drag from the propulsion system (prop, shaft or the like).

The most significant disadvantage to this system on recreational boats is definitely the deployment of the foils. Unless you want the added draft of these struts sticking down below your hull all the time, you must be able to extend and withdraw them — a complex engineering feat. There is at least one recreational powerboat employing hydrofoils: Twin Vee builds a catamaran with foils that don’t actually lift the hulls completely out of the water. It does improve fuel economy and ride stability nonetheless. Still, boats ride more smoothly in a sea and go much faster with hydrofoils. With the dramatic acceptance of this technology in sailing, is it only a matter of time before recreational powerboats incorporate foils into their designs?

Ulstein X-Bow The Norwegian Ulstein Group has been designing offshore vessels since 1917. Presently, it has the notoriety of creating the most advanced bow design in history. The Ulstein X-Bow looks like it might be upside down, but it’s proven itself in more than 100 offshore support vessels to date. The X-Bow allows higher speeds and smoother rides in even the worst seas. Gone are the slamming and vibration that occur when the bow of a ship drops off a wave. It functions better on all points of sea, and its lower hydrodynamic drag substantially decreases fuel consumption. The X-Bow has proven so successful that Ulstein is in the process of creating an X-Stern design now.

You won’t ever see this on small recreational boats, but you can nod knowingly when someone points one out on a mega-yacht in the near future.

• More: Boats

Boat Test: 2024 Bayliner Trophy T23 Pilothouse

Boat Test: 2024 Nuova Jolly Prince 33 CC

Boat Test: 2024 Starcraft SVX 231 OB CC

Boat Test: 2024 Bass Cat Caracal STS

I Learned About Boating From This: Capsize, Rescue and Lessons Learned

Boat Test: 2024 Regal 38 Surf

• Digital Edition
• Customer Service
• Privacy Policy
• Cruising World
• Sailing World
• Salt Water Sportsman
• Sport Fishing
• Wakeboarding

Many products featured on this site were editorially chosen. Boating may receive financial compensation for products purchased through this site.

Copyright © 2024 Boating Firecrown . All rights reserved. Reproduction in whole or in part without permission is prohibited.

My Cruiser Life Magazine

Basics of Sailboat Hull Design – EXPLAINED For Owners

There are a lot of different sailboats in the world. In fact, they’ve been making sailboats for thousands of years. And over that time, mankind and naval architects (okay, mostly the naval architects!) have learned a thing or two.

If you’re wondering what makes one sailboat different from another, consider this article a primer. It certainly doesn’t contain everything you’d need to know to build a sailboat, but it gives the novice boater some ideas of what goes on behind the curtain. It will also provide some tips to help you compare different boats on the water, and hopefully, it will guide you towards the sort of boat you could call home one day.

Table of Contents

Displacement hulls, semi displacement hulls, planing hulls, history of sailboat hull design, greater waterline length, distinctive hull shape and fin keel designs, ratios in hull design, the hull truth and nothing but the truth, sail boat hull design faqs.

Basics of Hull Design

When you think about a sailboat hull and how it is built, you might start thinking about the shape of a keel. This has certainly spurred a lot of different designs over the years, but the hull of a sailboat today is designed almost independently of the keel. 

In fact, if you look at a particular make and model of sailboat, you’ll notice that the makers often offer it with a variety of keel options. For example, this new Jeanneau Sun Odyssey comes with either a full fin bulb keel, shallow draft bulb fin, or very shallow draft swing keel. Where older long keel designs had the keel included in the hull mold, today’s bolt-on fin keel designs allow the manufacturers more leeway in customizing a yacht to your specifications.

What you’re left with is a hull, and boat hulls take three basic forms.

• Displacement hull
• Semi-displacement hulls
• Planing hulls

Most times, the hull of a sailboat will be a displacement hull. To float, a boat must displace a volume of water equal in weight to that of the yacht. This is Archimedes Principle , and it’s how displacement hulled boats get their name.

The displacement hull sailboat has dominated the Maritimes for thousands of years. It has only been in the last century that other designs have caught on, thanks to advances in engine technologies. In short, sailboats and sail-powered ships are nearly always displacement cruisers because they lack the power to do anything else.

A displacement hull rides low in the water and continuously displaces its weight in water. That means that all of that water must be pushed out of the vessel’s way, and this creates some operating limitations. As it pushes the water, water is built up ahead of the boat in a bow wave. This wave creates a trough along the side of the boat, and the wave goes up again at the stern. The distance between the two waves is a limiting factor because the wave trough between them creates a suction. 

This suction pulls the boat down and creates drag as the vessel moves through the water. So in effect, no matter how much power is applied to a displacement hulled vessel, it cannot go faster than a certain speed. That speed is referred to as the hull speed, and it’s a factor of a boat’s length and width. 

For an average 38 foot sailboat, the hull speed is around 8.3 knots. This is why shipping companies competed to have the fastest ship for many years by building larger and larger ships.

While they might sound old-school and boring, displacement hulls are very efficient because they require very little power—and therefore very little fuel—to get them up to hull speed. This is one reason enormous container ships operate so efficiently. 

Of course, living in the 21st century, you undoubtedly have seen boats go faster than their hull speed. Going faster is simply a matter of defeating the bow wave in one way or another.

One way is to build the boat so that it can step up onto and ride the bow wave like a surfer. This is basically what a semi-displacement hull does. With enough power, this type of boat can surf its bow wave, break the suction it creates and beat its displacement hull speed.

With even more power, a boat can leave its bow wave in the dust and zoom past it. This requires the boat’s bottom to channel water away and sit on the surface. Once it is out of the water, any speed is achievable with enough power. 

But it takes enormous amounts of power to get a boat on plane, so planing hulls are hardly efficient. But they are fast. Speedboats are planing hulls, so if you require speed, go ahead and research the cost of a speedboat . 

The most stable and forgiving planing hull designs have a deep v hull. A very shallow draft, flat bottomed boat can plane too, but it provides an unforgiving and rough ride in any sort of chop.

If you compare the shapes of the sailboats of today with the cruising boat designs of the 1960s and 70s, you’ll notice that quite a lot has changed in the last 50-plus years. Of course, the old designs are still popular among sailors, but it’s not easy to find a boat like that being built today.

Today’s boats are sleeker. They have wide transoms and flat bottoms. They’re more likely to support fin keels and spade rudders. Rigs have also changed, with the fractional sloop being the preferred setup for most modern production boats.

Why have boats changed so much? And why did boats look so different back then?

One reason was the racing standards of the day. Boats in the 1960s were built to the IOR (International Offshore Rule). Since many owners raced their boats, the IOR handicaps standardized things to make fair play between different makes and models on the racecourse.

The IOR rule book was dense and complicated. But as manufacturers started building yachts, or as they looked at the competition and tried to do better, they all took a basic form. The IOR rule wasn’t the only one around . There were also the Universal Rule, International Rule, Yacht Racing Association Rul, Bermuda Rule, and a slew of others. 

Part of this similarity was the rule, and part of it was simply the collective knowledge and tradition of yacht building. But at that time, there was much less distance between the yachts you could buy from the manufacturers and those setting off on long-distance races.

Today, those wishing to compete in serious racing a building boat’s purpose-built for the task. As a result, one-design racing is now more popular. And similarly, pleasure boats designed for leisurely coastal and offshore hops are likewise built for the task at hand. No longer are the lines blurred between the two, and no longer are one set of sailors “making do” with the requirements set by the other set. 

Modern Features of Sailboat Hull Design

So, what exactly sets today’s cruising and liveaboard boats apart from those built-in decades past? 

Today’s designs usually feature plumb bows and the maximum beam carried to the aft end. The broad transom allows for a walk-through swim platform and sometimes even storage for the dinghy in a “garage.”

The other significant advantage of this layout is that it maximizes waterline length, which makes a faster boat. Unfortunately, while the boats of yesteryear might have had lovely graceful overhangs, their waterline lengths are generally no match for newer boats. 

The wide beam carried aft also provides an enormous amount of living space. The surface area of modern cockpits is nothing short of astounding when it comes to living and entertaining.

If you look at the hull lines or can catch a glimpse of these boats out of the water, you’ll notice their underwater profiles are radically different too. It’s hard to find a full keel design boat today. Instead, fin keels dominate, along with high aspect ratio spade rudders. 

The flat bottom boats of today mean a more stable boat that rides flatter. These boats can really move without heeling over like past designs. Additionally, their designs make it possible in some cases for these boats to surf their bow waves, meaning that with enough power, they can easily achieve and sometimes exceed—at least for short bursts—their hull speeds. Many of these features have been found on race boats for decades.

There are downsides to these designs, of course. The flat bottom boats often tend to pound when sailing upwind , but most sailors like the extra speed when heading downwind.

How Do You Make a Stable Hull

Ultimately, the job of a sailboat hull is to keep the boat afloat and create stability. These are the fundamentals of a seaworthy vessel. 

There are two types of stability that a design addresses . The first is the initial stability, which is how resistant to heeling the design is. For example, compare a classic, narrow-beamed monohull and a wide catamaran for a moment. The monohull has very little initial stability because it heels over in even light winds. That doesn’t mean it tips over, but it is relatively easy to make heel. 

A catamaran, on the other hand, has very high initial stability. It resists the heel and remains level. Designers call this type of stability form stability.

There is also secondary stability, or ultimate stability. This is how resistant the boat is to a total capsize. Monohull sailboats have an immense amount of ballast low in their keels, which means they have very high ultimate stability. A narrow monohull has low form stability but very high ultimate stability. A sailor would likely describe this boat as “tender,” but they would never doubt its ability to right itself after a knock-down or capsize.

On the other hand, the catamaran has extremely high form stability, but once the boat heels, it has little ultimate stability. In other words, beyond a certain point, there is nothing to prevent it from capsizing. 

Both catamarans and modern monohulls’ hull shapes use their beams to reduce the amount of ballast and weight . A lighter boat can sail fast, but to make it more stable, naval architects increase the beam to increase the form stability.

If you’d like to know more about how stable a hull is, you’ll want to learn about the Gz Curve , which is the mathematical calculation you can make based on a hull’s form and ultimate stabilities. 

How does a lowly sailor make heads or tails out of this? You don’t have to be a naval architect when comparing different designs to understand the basics. Two ratios can help you predict how stable a design will be .

The first is the displacement to length ratio . The formula to calculate it is D / (0.01L)^3 , where D is displacement in tons and L is waterline length in feet. But most sailboat specifications, like those found on  sailboatdata.com , list the D/L Ratio.

This ratio helps understand how heavy a boat is for its length. Heavier boats must move more water to make way, so a heavy boat is more likely to be slower. But, for the ocean-going cruiser, a heavy boat means a stable boat that requires much force to jostle or toss about. A light displacement boat might pound in a seaway, and a heavy one is likely to provide a softer ride.

The second ratio of interest is the sail area to displacement ratio. To calculate, take SA / (D)^0.67 , where SA is the sail area in square feet and D is displacement in cubic feet. Again, many online sites provide the ratio calculated for specific makes and models.

This ratio tells you how much power a boat has. A lower ratio means that the boat doesn’t have much power to move its weight, while a bigger number means it has more “get up and go.” Of course, if you really want to sail fast, you’d want the boat to have a low displacement/length and a high sail area/displacement. 

Multihull Sailboat Hulls

Multihull sailboats are more popular than ever before. While many people quote catamaran speed as their primary interest, the fact is that multihulls have a lot to offer cruising and traveling boaters. These vessels are not limited to coastal cruising, as was once believed. Most sizable cats and trimarans are ocean certified.

Both catamarans and trimaran hull designs allow for fast sailing. Their wide beam allows them to sail flat while having extreme form stability. 

Catamarans have two hulls connected by a large bridge deck. The best part for cruisers is that their big surface area is full of living space. The bridge deck usually features large, open cockpits with connecting salons. Wrap around windows let in tons of light and fresh air.

Trimarans are basically monohulls with an outrigger hull on each side. Their designs are generally less spacious than catamarans, but they sail even faster. In addition, the outer hulls eliminate the need for heavy ballast, significantly reducing the wetted area of the hulls. 

Boaters and cruising sailors don’t need to be experts in yacht design, but having a rough understanding of the basics can help you pick the right boat. Boat design is a series of compromises, and knowing the ones that designers and builders take will help you understand what the boat is for and how it should be used. 

What is the most efficient boat hull design?

The most efficient hull design is the displacement hull. This type of boat sits low in the water and pushes the water out of its way. It is limited to its designed hull speed, a factor of its length. But cruising at hull speed or less requires very little energy and can be done very efficiently. 

By way of example, most sailboats have very small engines. A typical 40-foot sailboat has a 50 horsepower motor that burns around one gallon of diesel every hour. In contrast, a 40-foot planing speedboat may have 1,000 horsepower (or more). Its multiple motors would likely be consuming more than 100 gallons per hour (or more). Using these rough numbers, the sailboat achieves about 8 miles per gallon, while the speedboat gets around 2 mpg.

What are sail boat hulls made of?

Nearly all modern sailboats are made of fiberglass. 

Traditionally, boats were made of wood, and many traditional vessels still are today. There are also metal boats made of steel or aluminum, but these designs are less common. Metal boats are more common in expedition yachts or those used in high-latitude sailing.

Matt has been boating around Florida for over 25 years in everything from small powerboats to large cruising catamarans. He currently lives aboard a 38-foot Cabo Rico sailboat with his wife Lucy and adventure dog Chelsea. Together, they cruise between winters in The Bahamas and summers in the Chesapeake Bay.

Welcome to Lake

Discover places to stay and unique experiences around the world.

• How It Works

Home - Blog - Catamarans Uncovered: The Ultimate Guide to Dual-Hulled Sailing

Catamarans Uncovered: The Ultimate Guide to Dual-Hulled Sailing

David Ciccarelli

January 27, 2024

In this article

Get started.

Understanding Catamarans

When you think of sailing through turquoise seas, what comes to your mind? If you’re picturing luxurious, spacious boats that glide smoothly over water, then you’re probably thinking of catamarans. These multi-hulled marvels are not your average boats; they’re about stability, space, and speed. Let’s set sail on understanding what makes them so unique.

Catamaran Basics

Catamarans are characterized by their two parallel hulls, which fundamentally distinguish them from the traditional monohull vessels. This twin-hull design often results in a wider beam, creating an inherently stable platform. While they boast a shallower draft compared to monohulls, catamarans generally provide more living space and less heeling. With less resistance in the water, performance catamarans can achieve greater speeds. The typical displacement of these vessels means they sit on top of the water rather than plowing through it, which adds to their efficiency.

Historical Evolution

The history of the catamaran dates back thousands of years, with its roots in the fishing and transportation crafts of the ancient Polynesians. Through generations, the design has evolved from simple canoes with outriggers to the sleek, modern vessels we see today. From rudimentary construction to high-tech materials, catamarans have adapted to become a favorite in both private and commercial sectors.

Types of Catamarans

If we list out the types of catamarans, you’d encounter various classes tailored to different sailing needs. You have your cruising catamarans, spacious and comfortable, ideal for those leisurely voyages. There’s the more agile performance catamarans, designed with speed and responsiveness in mind. And then, the luxury catamarans—think of these as floating mansions, complete with opulent amenities and furnishings.

Sailing Catamarans

Your sailing catamarans are akin to dancers on water. With sails harnessing the power of the wind, these vessels are all about eco-friendly propulsion and an authentic sailing experience . Imagine gliding past coastlines without a noise except for the wind in the sails and the water against the hulls. Brands like Lagoon and Fountaine Pajot have become synonymous with this category, providing a range of options from small day sailors to majestic cruisers.

Power Catamarans

Power catamarans, as the name suggests, rely on engines for movement. These are the go-to for those who prefer a bit more oomph in their voyage—capable of higher speeds and longer range without wind dependence. They’re perfect if you’re into coastal hopping or even deep-sea adventures.

Luxury Catamarans

Indulge yourself with luxury catamarans, the epitome of elegance on the water. These vessels come with full crews, gourmet meals, and the kind of pampering you’d expect at a 5-star resort. They represent the pinnacle in comfort and amenities , often custom-designed to meet the desires of the most discerning sailors.

Let’s pause for a breath—feeling the breeze yet? Catamarans are indeed a special breed of vessels that combine innovation, comfort, and performance. So next time you dream of sailing, think of these dual-hulled wonders and consider that perhaps your next adventure awaits on board a catamaran.

Catamaran Design and Construction

Catamarans are unique in the boating world, offering stability, space, and speed that many sailors dream of. Whether you’re an enthusiast or a prospective buyer, understanding the intricacies of catamaran design and construction is essential. Have you ever wondered what goes into making these remarkable multihull vessels?

Multihull Structure

Multihull vessels, such as catamarans, are defined by their two separate hulls. This design provides natural stability which is excellent for reducing seasickness. A significant advantage here is safety ; with two hulls, even if one becomes flooded, the catamaran can often remain afloat and upright.

The Dual-Hull Design

The dual-hull design of catamarans allows for a wider beam, which translates into more deck space. When compared to monohulls, catamarans don’t heel over, making your experience onboard more comfortable and safer. This design also means less resistance when cutting through water, increasing your speed potential.

Advantages of Multihulls

Catamarans are renowned for their spaciousness and comfort, but did you know they tend to have a shallower draft? This allows you to easily explore shallower waters where other boats can’t go. Additionally, they are often faster, making them a favorite for both racing and cruising.

Materials and Construction

When building catamarans, manufacturers often utilize lightweight materials to enhance performance without compromising strength. Composites like fiberglass are common due to their durability and ease of maintenance .

Building Catamarans

The process of building catamarans involves meticulous planning and precision. Each step, from the initial design to the final touches, aims for a blend of performance and comfort. The popularity of DIY catamaran kits has also risen, catering to those who wish to take a hands-on approach to their vessel.

Composite vs. Aluminum

Catamarans can be built from various materials, but the debate often falls between composites and aluminum. Composites are prized for their strength-to-weight ratio, while aluminum is favored for its toughness and repairability. The choice depends on the intended use and the desired balance between weight and durability.

Rigging and Sails

The rigging and sails are critical in determining a catamaran’s performance. With more sail area, catamarans capture a greater amount of wind, which can improve speed. However, the sail plan must be carefully designed to balance power and handling .

Sail Configuration

Choosing the right sail configuration depends on your sailing needs. For travelers who prefer easier handling , a simple sloop rig with one mainsail and one foresail may suffice. Alternatively, performance-oriented sailors might opt for additional sails like spinnakers for downwind speed.

Sail Handling Systems

Modern catamarans incorporate advanced sail handling systems to make sailing more manageable, even for smaller crews. Features such as roller furling for the jib and lazy jacks for the mainsail simplify sail deployment and retrieval, which can be a real back saver!

So, have you gotten a clearer picture of what goes into a catamaran’s design and construction? Whether it’s the material selection or the intricacies of sail handling, each aspect plays a part in giving you the ultimate experience on the water.

Key Features and Advantages

When you’re in the market for a boat that embodies comfort and performance, a catamaran is hard to beat. Let’s dive into what makes these vessels a standout choice for sailors and how they might just be your ticket to the ultimate sailing adventure.

Stability and Safety

Catamarans are renowned for their stability on the water, which translates into increased safety during your maritime excursions. Thanks to their wide beams, which can significantly exceed those of monohulls, moments of discomfort from rolling are minimized whether you’re at anchor or cutting through the waves.

Reduced Risk of Capsizing

The dual hulls of a catamaran are not just for show; they inherently provide a lower center of gravity and a wider base, which greatly decreases the odds of capsizing, giving you peace of mind as you navigate various sea conditions.

Safe Sailing in Rough Waters

One of the greatest perks of catamarans is their capability to handle rough waters with aplomb. The vessel’s design allows for quick and responsive movement, which is crucial when you’re miles from shore and conditions become challenging.

Spaciousness and Comfort

A catamaran is synonymous with spaciousness. Due to the dual hull construction, you’ll find ample living spaces comparable to a floating apartment, making long passages or entertaining guests a delightful experience.

Ample Deck Space

Have you dreamed of a boat where you can lounge, dine, and play without feeling cramped? A catamaran’s deck provides generous outdoor living areas, perfect for soaking up the sun or enjoying al fresco meals with a view of the ocean’s expanse.

Comfortable Living Spaces

Below deck, catamarans boast comfortable living quarters with enough headroom and sizeable cabins . The separation between sleeping areas, often located in different hulls, also ensures privacy that’s hard to come by in other vessel types.

Speed and Efficiency

With a sleek design and lighter weight, catamarans can glide through water quickly and with less effort. Their speed capability is not just great for thrill-seekers but also for those who wish to cover significant distances in tighter timeframes.

Fuel Efficiency in Power Catamarans

For power catamaran lovers, the efficiency game is strong. These cats are designed to consume less fuel while maintaining speed, leading to long-term savings and a reduced environmental footprint.

Ocean Cruising Capabilities

A catamaran truly shines when it comes to blue water cruising. The vessel’s stability and performance make this type of boat well-suited for exploring a variety of destinations across the globe.

Long-Distance Cruising Comfort

Planning an overnight or multi-day cruise? Catamarans are equipped to provide exceptional comfort during long-distance journeys, allowing you to reach far-off places like the Caribbean or South Pacific with ease and pleasure.

Catamarans for World Travel

Imagine setting sail to any corner of the world in a boat that feels like home. Catamarans offer that potential with their excellent cruising capabilities, capacity for provisions and fuel, and comfort—making them ideal for the adventurous sailor eager to chart a course for exotic destinations.

Remember, catamarans by brands like Lagoon or Fountaine Pajot are not only a statement of luxury but also showcase the pinnacle of marine engineering designed with your sailing lifestyle in mind. Ready to catch the wind in your sails?

Notable Catamaran Brands and Models

When you’re out on the open waters, the brand and model of your catamaran are as important as the wind in your sails. Let’s talk about some of the most revered names that have made waves in the world of catamarans.

Lagoon Catamarans

Lagoon is a French manufacturer that’s taken the catamaran market by storm. Known for a blend of innovation and tradition, these catamarans have a strong global presence.

Since its inception in 1984, Lagoon has become synonymous with high-quality catamaran craftsmanship. Their journey began as a segment of the illustrious Group Beneteau, sailing onto becoming a standalone brand admired by many.

Fountaine Pajot

Fountaine Pajot , another French marvel, has carved its niche in the luxury catamaran market since 1976, delivering elegance and sturdiness in every vessel.

Awarded multiple times, including ‘Boat of the Year’, Fountaine Pajot’s reputation is built on innovation, performance, and eco-friendly designs. They are a marquee name for discerning sailors looking for the French touch in boating excellence.

Leopard Catamarans

South African-built Leopard Catamarans offer a robust build quality and a luxury cruising experience that appeals to adventurers and comfort-seekers alike.

Leopard has consolidated its status in the catamaran domain with models like the Leopard 48, known for its innovative design and exceptional onboard amenities.

In your quest for the perfect catamaran, these brands and models stand as shining beacons of quality and expertise. Each one has a story to tell and a journey to offer, ready to make your seafaring dreams a reality. Which one will you choose for your next maritime adventure?

Choosing the Right Catamaran

When you’re on the hunt for the perfect catamaran, the choices can be as vast as the ocean itself. From understanding the key differences between sail and power options to considering your unique sailing style and budget, we’ve got the guidelines to help you navigate this significant investment.

Sail vs. Power Catamaran

Sail catamarans are beloved for their elegance and eco-friendly operation. You’re harnessed to the wind, often yielding better performance and lower operating costs. Power catamarans, on the other hand, offer more consistent speeds regardless of wind conditions and typically feature more living space.

Considering Your Sailing Style

Whether you’re dreaming of leisurely coastal cruises or ambitious ocean crossings, your sailing style is crucial. For example, a sail catamaran with a deep draft improves windward performance for long voyages, while a power catamaran might be the ticket for weekend jaunts and entertaining.

Pros and Cons of Power Catamarans

Power catamarans excel in ease of handling and spaciousness. However, they typically have higher fuel costs, so consider this when comparing prices.

Size and Capacity

Determining boat size.

The size of your catamaran impacts everything from displacement to comfort. Larger models above 40 feet can offer 5 cabins, ample deck space, and enough storage for extended cruising. However, bigger boats also mean higher costs.

Passenger Capacity and Comfort

A catamaran’s design optimally balances capacity and comfort. Here’s a quick reference:

• 2-3 cabins : Ideal for small families or couples.
• 4 cabins : Good for larger groups or charter businesses.
• 5+ cabins : Best for commercial use or those who entertain regularly.

Budget Considerations

Costs of catamarans.

The price of a new catamaran can range from a modest $200,000 to over a million dollars for luxury brands like Leopard Catamarans. Used models can bring significant savings, but factor in potential upgrade and maintenance costs.

Ongoing Expenses

Beyond the purchase price, be prepared for expenses such as docking fees, maintenance, insurance , and of course, fuel for power cats. The latter can significantly affect your budget, especially if you plan to log many nautical miles.

Finding the catamaran that suits your lifestyle, performance expectations, and budget is both an exciting and intensive process. Remember to weigh all factors carefully to ensure your final decision is one that brings endless days of joy on the water.

Maintenance and Care

Taking care of your catamaran not only keeps it looking great but also ensures it performs optimally for years to come. Regular maintenance can prevent costly repairs and extend the life of your boat. Let’s dive right into the nitty-gritty of keeping your cat pristine, shall we?

Essential Maintenance Tasks

“Prevention is better than cure,” they say, and it couldn’t be truer for your catamaran.

• Hull Cleaning : It’s all about the smooth sail, isn’t it? Keep the hull free from marine growth with bi-annual clean-ups.
• Electrical System: Battling corrosion is like facing the high winds at sea. Keep your electrical systems corrosion-free to prevent unexpected failures.

Maintenance Schedule

Sticking to a maintenance schedule is akin to following a treasure map – it leads you to the golden prize of a well-maintained vessel. For instance, oil should be changed at least every 150 hours of engine use.

• Routine Check-Ups: Don’t forget to schedule these with the changing seasons, folks.
• Professional Inspections: Sometimes, you need a seasoned pair of eyes. Yearly check-ups by a professional can spot issues you might miss.

Cleaning and Storage

A clean and well-stored catamaran means a ready-to-go boat when sailing season hits. Nobody likes a damp surprise onboard, right?

• Dry Storage: Whenever possible, store your beloved cat on dry land.
• Cover Up: Use a high-quality cover to shield from the elements – sun, rain, or residents of the nearby trees.

Cleaning Procedures for Catamarans

This is not just a splash-and-dash affair, my friends. Take heed of these steps:

• Freshwater Rinse: After every outing, a freshwater rinse can do wonders against saltwater’s corrosive embrace.
• Mild Soaps: Use gentle cleaners like Woolite or Dawn to keep that canvas looking dapper.

Off-Season Storage Tips

The off-season doesn’t mean rest for you. It’s prime time to ensure your catamaran rests well so it’s adventure-ready when you are.

• Ventilation: Keep air circulating to thwart the ever-creeping mildew.
• Battery Care: Don’t let your batteries go flat. Keep them charged and happy during the off-season.

From the yearly varnishing to the regular freshwater rinses, keeping your catamaran in sparkling condition is a rewarding journey. It’s not just about maintaining value; it’s about cherishing the vessel that carries you across the waters, creating memories one nautical mile at a time. So grab your maintenance kit and let’s keep those cats cruising!

Sailing Safety and Regulations

Ensuring your safety while enjoying the freedom of sailing on a catamaran involves understanding and adhering to essential safety practices and boating regulations. In this section, we’ll navigate through the crucial elements of safety onboard, understand the necessary equipment, and explore the legal requirements that keep you compliant and secure at sea.

Safety Equipment on Catamarans

Catamarans must be equipped with certain safety gear. It’s imperative that your vessel has life jackets for all passengers, fire extinguishers, visual distress signals, and other USA Coast Guard approved safety equipment. Have you checked your boat’s safety inventory recently?

Safety Guidelines for Catamaran Sailing

When you’re sailing a catamaran, it’s wise to “know before you go.” This means checking weather reports and understanding your boat’s limitations. For catamaran-specific tips, remember that while daggerboards or keels enhance performance, they should be handled with care, as they affect the vessel’s stability and maneuvering.

Boating Regulations

Did you know that boating regulations can vary by state and region? It’s not just about being legally compliant; understanding these regulations helps protect the marine environment and ensures that all boaters can enjoy shared waterways safely. Have a look at the U.S. Coast Guard Boating Safety regulations to stay updated.

Adhering to Maritime Laws

Finally, respecting maritime laws and customs is not only a legal obligation but also a mark of a responsible sailor. Here’s a compelling fact: strict adherence to maritime laws significantly reduces the risk of maritime accidents. So, keep abreast of navigation rules to ensure smooth sailing.

Remember, safety is the keel that keeps the exciting adventure of catamaran sailing stable and enjoyable – make sure it’s part of your voyage every time you cast off the lines. Now, are you ready to take the helm knowing you’re well-prepared for a safe journey?

FAQs (Frequently Asked Questions)

What are the advantages of sailing on a catamaran.

You’re in for a treat with catamarans — they’re like the luxury SUVs of the sea but without the fuel guzzling. Expect sheer stability, more living space, and less heeling than a monohull.

How Much Does a Catamaran Cost?

Thought about owning one of these beauties? Keep in mind, the sticker price varies wildly. We’re talking anywhere from $100,000 for a modest pre-owned vessel to north of a couple of million for a brand-spanking-new one, outfitted for luxury. Remember to factor in maintenance costs, which can set you back a few grand a year.

Are Catamarans Suitable for Family Vacations?

Absolutely, your clan will love the spacious decks and cabins that catamarans provide. It’s like a floating condo with the best ocean views.

What Safety Equipment Should I Have on Board a Catamaran?

Your catamaran should be your safe sanctuary on the seas. So gear up with life jackets, flares, VHF radios, and a dinghy for starts. Also, a solid first-aid kit and safety harnesses are invaluable.

administrator

David Ciccarelli, is the Founder and CEO of Lake. He is based in Toronto, Canada, and is an expert in management, business administration, strategy, product development, and customer experience. His educational achievements include the Owner President Management Program at Harvard Business School (2019-2022) and the QuantumShift Program at Ivey Business School in 2017, aimed at CEOs of growing businesses.

Related Posts

October 3, 2023

Lake House Rentals: Your Ultimate Getaway Guide for 2023

Lake houses are charming abodes that offer stunning waterfront views and bring a sense of ...

Boating: Your 10-Step Guide to Driving a Boat Safely

Boating is a fantastic way to take advantage of the great outdoors and create unforgettabl...

October 4, 2023

Water Skiing Essentials: Tips and Tricks for a Thrilling Experience

Water skiing is an exhilarating surface water sport where individuals ride on one or two s...

Don't have an account yet? Register

Already have an account? Sign In

Reset Password

Please enter your username or email address, you will receive a link to create a new password via email.

Shape & Resistance

A boat's hull shape and the distribution of volume are key factors in determining how it will behave in varying wind and load conditions. The underwater characteristics of a vessel are responsible for allowing a multihull and its cargo to travel through the water. The faster and more effortlessly the twin hulls can displace the surrounding fluid, the less resistance and more efficient a catamaran will be.

Typically modern catamaran designs have sharp bows to drive the vessel through the seas with as little wave making as possible. High freeboard assures a dry ride. Ample buoyancy helps keep the stems out of the water and spray to a minimum. Elliptical sections make up the first third of the hull, providing an easy entry in the water and some means to resist leeway. Towards the middle of the boat, gradually flattening out towards the stern, the sections become semicircular to help distribute buoyancy. These portions help carry payload and facilitate the hull lifting at speed. Basically, the majority of all cruising catamarans share these same underwater features.

Decades ago very seakindly, double-ended hull shapes were the norm as found in the thousands of Wharram catamarans. They were easy to construct, relatively slippery, and provided ample freeboard. Unfortunately they could not carry a lot of cruising gear, had cramped accommodations and were not the best windward performers. Their sharp V-sectioned hulls and rudders were their only means of resisting leeway as they had no leeway preventing devices. Similarly, the narrow asymmetrical type hull, such as found in the Hobie 16 beach catamaran, is hardly used in today's cruising multihull. The idea was to keep the underwater appendage to a minimum and eliminate any keels or daggerboards.

In contrast, the modern catamaran benefits from tank testing and computer-aided design. Composite molding technology allows for infinite shapes and each designer or manufacturer can now realize his idea of the perfect hull shape. Today's mini keels and daggerboards keep the cat hard on the wind and rival the weatherliness of monohull racers.

Drag on the hulls is the main deterrent to speed and has many components. We have to distinguish between water and air drag. Water-induced resistance can be further broken down into drag caused by wetted surface and wave making. Wetted surface, which is the frictional resistance the hulls experience when they are passing through the water, is the main cause of resistance at low speed. Wave making becomes more important as boat speed exceeds hull speed , or 1.34 x square root of the waterline length. Wave making resistance is not as easy to analyze and is more complex than drag caused by wetted surface; it is primarily a function of weight and, secondarily, of hull shape.

Pitch is another form of drag which can slow the boat down. This unwanted phenomenon is directly related to the buoyancy of the extremities and weight distribution. Wave-making resistance caused by the boat's constant plunging will slow a multihull, especially since it has less momentum to drive it through waves as compared to a single-hulled vessel. In addition the airflow over the sails will be disturbed by a constant change of attitude, further hindering efficient progress. Pitching can also be caused by placing items that are too heavy into the extreme ends of the multihull. In addition, various design- and construction-related issues can cause this problem, such as bridge decks extending too far forward of the mast and a high, heavy rig. Solid decking instead of trampoline nets, and/or large protrusions, which strangely some manufacturers claim break up waves, can also cause a hobby-horsing effect. Not only can this result in more wave-making drag than desired, but can seriously tire the crew. Any structure ahead of the mast can cause major slamming when having to face steep seas. Although many cruising catamarans, such as the Prouts, have been built with large bridgedeck structures extending forward to the bows, it is my opinion that an open trampoline, which poses no resistance to wind and seas, is imperative on a good cruising cat.

above High freeboard and angled-out hulls are trademark features of this capable Catana 521. Much thinking has gone into the hull shape of this catamaran, yet the pronounced step running along the inside of the vessel might create some wave slap in some conditions, a typical example of a compromise between space and performance.

Resistance & Performance

Resistance vs. Speed of four different vessel configurations

A. Traditional, heavy displacement monohull cruiser

B. ULD (Ultra Light Displacement) monohull

C. Typical performance catamaran cruiser

D. Racing multihull, with almost no wave making resistance below A popular French catamaran, as photographed out of the water at the Paris Boat Show . Note that there are barely several inches of clearance between the bridgedeck and waterline. The pronounced forward knuckle of the nacelle is claimed to break up waves. In my mind however, there is very little that can resist the continued impact of seas, and any conflict between the wingdeck and waves should be avoided.

Continue reading here: Catamaran Sailboat Wide Bodied Hulls

Was this article helpful?

Recommended Programs

Myboatplans 518 Boat Plans

Boat Alert Hull ID History Search

3D Boat Design Software Package

Related Posts

• Catamaran Design Guide - Catamarans Guide
• Design Dynamics - Catamarans Guide
• Hull Hydrodynamics and Design
• Catamaran vs Monohull - Catamarans Guide

Readers' Questions

What is a characteristic of a catamaran hull?

A characteristic of a catamaran hull is that it has two parallel hulls, which provide greater stability than a monohull vessel and help reduce roll, pitch and yaw. Catamarans also generally require less power to achieve a given speed than a monohull and provide improved handling characteristics in open water.

What may cause hull on catamaran to bend?

Hull flexing on catamarans may be caused by several factors, such as high winds, strong waves, heavy loads, and improper loading. Poorly designed or constructed hulls can also be more vulnerable to flexing.

How to construct catermaran hull show pictures?

Unfortunately, it is not possible to construct a catamaran hull with pictures alone. A catamaran hull is a complex structure that requires precise measurements and calculations in order to ensure that it is structurally sound and performs optimally when in the water. If you would like to learn more about constructing a catamaran hull, you should refer to resources such as books, websites, and experienced boat builders who can provide you with detailed instructions.

How far should a catamaran bridge be of the water?

The height of a catamaran bridge will depend on the size and type of the catamaran. Generally, a bridge should be slightly above the water line, typically between 6 and 12 inches.

How to get catamaran hull resistance?

Catamaran hull resistance is determined by a number of factors, such as the shape of the hull, length and beam dimensions, wetted surface area, type of appendages, and underwater profile. To determine the resistance, the hull needs to be tested in a towing tank or in the open water. The resistance coefficients obtained by testing can then be used to calculate the total resistance of the catamaran hull.

• USA +1 954 892 5009
• UK +44 (0)20 7193 5450

• Crewed Yachts
• Destinations

The Cool Cats: Exciting New Developments in Sustainable Catamaran Design

The catamaran fleet has long been admired for its stability, speed, and versatility with its unique multi-hull design. Today they are also hailed as being more sustainable than the conventional monohull. 

With so many builders in the industry pushing the boundaries on the multi-hull scene, a new wave of sustainable concepts is revolutionizing the industry. 

As soon as these concepts hit the water, we will offer them for charter on Boatbookings – check for them on our crewed charter catamarans .

Design elements: electrification, new materials, energy efficiency 

There are various factors that designers now take into account when launching new catamaran concepts and designs, with sustainability seemingly at the forefront. 

• Electric propulsion: Transitioning from conventional fuel-powered engines to electric propulsion systems is a significant step in sustainability. Electric motors offer zero-emission operation, minimizing both air and water pollution. In addition to this, there have been advancements in battery technology to increase the range and efficiency. Scroll down to take more of a read on electric yachting in our previous post.  Oh, and they don’t stink of noxious fumes when you’re swimming near them!
• Lightweight and eco-friendly materials: Utilising lightweight and eco-friendly materials reduces the catamaran’s weight and enables enhanced fuel efficiency and reduced emissions. Flax fiber composites are one such material. Flax is a fibrous plant that for centuries has provided the basis for linen, and can be used instead of glass fiber. It is lighter than glass and requires 2-5 times less energy to produce.
• Energy-efficiency : Catamaran design is now being optimized for reduced energy consumption. Through smart energy management systems, advanced multi-hull designs to reduce drag, and other factors such as LED lighting and the use of solar panels. 

Cool Cat Examples: 

We already have a range of electric crewed catamarans for you to choose from that are currently on the water, but below are some new concepts that have not yet splashed onto the charter market. We are very excited to see how these catamarans develop.

Alva yachts and their wings 

Alva Yachts has recently announced that the second yacht in its flagship 28-meter Ocean Eco 90 catamaran series has begun construction. The Ocean Eco 90 has a fully electric drive and hydrogen fuel cell. It will be powered by two performance electric motors connected to a 500 kWh battery pack, with power from solar panels. It will also be fitted with Gyro’s Oceanwings wind propulsion system. 

A Hybrid Launch by Rossinavi 

The Italian shipyard unveiled a new catamaran concept in collaboration with Zaha Hadid Architects, called Oneiric . The 44-meter eco-friendly vessel has solar energy at its core with four modes of operation. The hybrid concept can be fully-electric for day trips and adjusted for multi-day cruises. Its transatlantic range can be 80% electric and in ‘hibernation’ mode to allow it to be self-sufficient when in port. 

The Domus concept 

At over 40 meters long, this radical concept was designed by Van Geest Design and Rob Doyle Design. The Domus concept claims to be the first truly zero-emissions yacht over 750 gross tonnes. The design is supported by hydrogen fuel cells, hydrogenation, and solar energy. It also boasts an unlimited range. We can’t wait until these designs are the norm. 

Although on a smaller scale, these catamarans are nonetheless impressive. This 100% electric and renewable energy-driven catamaran is being launched this October. With a sleek and futuristic design, Mod X focuses on sustainability and efficiency, incorporating lightweight materials and eco-friendly systems. 

These concepts are only a few of the new designs being announced daily. Highlighting the fact that catamaran design harnesses innovative technologies, materials, and design principles to minimize their environmental impact and carbon emissions without compromising on performance and luxury. Contact the Boatbookings team if you want to be part of leading the change on green chartering today.

Comments are closed.

Rating: 4.9 / 5 calculated on 1287 reviews

Moskva-Class Cruisers

Separate design teams often attempt to meet a set of ship specifications with completely different, although equally valid, strategies. To fulfill the requirements issued in April 2169 for the successor (NX-223) to the Daedalus class, which was introduced at the end of the Romulan War, Prosser & Ankopitch proposed a ship with an extremely large, spherical command hull attached to a nearly vestigial engineering hull. The proposal from the Mikoyan-Tupolev-Dassault Bureau used a long narrow command hull with a minimal frontal silhouette counterbalanced by an equally long engineering hull.

The engineers at Tezuka-Republic decided that the division of ship's functions between a command/crew hull and an engineering hull was arbitrary and unnecessarily restricted design options. Therefore, rather than gathering all the specified facilities in a single hull, their design TR-223A spread them across two hulls, as in Daedalus , and segregated the SSWR-IV-C warp core to a "bustle" at the extreme aft end of the secondary hull. This bustle could be separated easily and quickly from the rest of the engineering hull in the event of a warp core breach. The now-unpowered warp nacelles would then be shed. In this way, the demands of safety would be met without warp dynamics being degraded either by an excessively large frontal silhouette or by longitudinal warp field imbalance.

Although the Ship Specifications Review Board praised Tezuka-Republic for its creative solution to the problem of admittedly contradictory requirements for extreme safety and improved warp performance, they were forced to disqualify design TR-223A for not precisely meeting contract specifications. Therefore, in October 2171, construction contract NX-223 for Starfleet's new cruiser was awarded to Prosser & Ankopitch for what would become the Wasp class .

However, almost no one was happy with the new Wasp ships. Even before the contract was awarded, voices within Starfleet and within industry had strongly criticized the specifications of April 2169. These critics charged that they would lead to a mediocre, albeit safe, fighting ship. Two separate classes were needed, not a single class that was neither a proper explorer nor a proper warship. When Wasp was finally launched in 2173, her performance during precommisioning trials clearly showed that the critics had been correct. Although the performance problems were related in part to the continuing unavailability of the more powerful Tezuka-Republic Hiryu ("Flying Dragon") mark III warp nacelles, Wasp was obviously not the ship Starfleet had hoped for.

In a second attempt to obtain a reliable and capable warship, new specifications (NX-374) were issued in September 2175, little more than a year after USS  Wasp had entered service. Adding to this sense of urgency were intelligence reports suggesting that the Romulans had either developed or otherwise acquired matter/antimatter (M/AM) reactors. This time the specifications put less emphasis upon safety. The original requirement for completely separate command and engineering hulls was eliminated; instead, any hull configuration was allowed as long as the warp core could be quickly separated from the rest of the ship. Furthermore, requirements for speed, acceleration, and maneuverability both under impulse power and under warp power were increased, as were performance levels for target acquisition, tracking, and servicing.

These new specifications were a clear, albeit belated, admission that the critics had been correct all along: one class could not be expected to serve as both an explorer and a main battleship. In fact, starship technology was not considered sufficiently mature for a single ship to adequately fulfill both mission profiles until 2245, when the Constitution -class heavy cruiser was launched. (The controversy continues even today in the wake of the problems of the Galaxy -class explorer.)

Luckily, the designers and engineers at Tezuka-Republic had not been idle since their disappointing loss of the Wasp contract in 2171. Instead, they had spent their time refining design TR-223A so that their new entry (TR-374A) was markedly superior to what had been submitted 5 years earlier. In particular, the new SSWR-V warp reactor allowed the bustle to be made smaller, lighter, and even more easily separable. Therefore, it was hardly surprising when in November 2176 Tezuka-Republic was awarded the production contract over designs from Shimata-Dominquez, Prosser & Ankopitch, Mikoyan-Tupolev Dassault, Monarch R&U, and Thornycroft/Ebisu for what was to become the Moskva class.

However, engineering prowess may not have been the only factor in Tezuka-Republic's winning of the contract. There were accusations that the delay in delivery of the Hiryu warp engines was an attempt by Tezuka-Republic to prevent Wasp from reaching her designed performance levels. While no conclusive incriminating evidence has come to light, the delivery of the long-awaited engines shortly before the scheduled launch of Moskva in December 2177 is certainly suspicious. Tezuka-Republic maintains that if their submission of 2169 had been selected, its performance would also have not have met design specifications without the Hiryu engines. However, critics charge that TR-223A was not as reliant as Wasp on the type of engine used. Furthermore, once the Wasp contract was awarded, and even after Wasp was launched, Tezuka-Republic certainly made no efforts to accelerate delivery of Hiryu.

These controversies were soon rendered moot as the new Moskva class was recognized as a significant advance in starship design. The most important new feature was Moskva's discoid primary hull. Earlier designs had chosen a spherical primary hull for reasons of economy. Simple geometric relationships dictate that a spherical hull has the smallest surface area for a given volume. Therefore, construction costs are lower and shields are more efficient. Furthermore, institutional inertia had led nearly all exploratory cruisers originating until that time from the National Aeronautics and Space Administration, the United States Astronautics Agency, the United Earth Space Probe Agency, and its successor organizations to have spherical hulls.

The designers of USS  Moskva employed a biconvex disc for several reasons. Their initial motive was to increase hull volume while minimizing both frontal and lateral silhouettes. A warship with large frontal and lateral silhouettes would be at a greater disadvantage in most tactical situations than would be a ship with an increased superior silhouette. However, the discoid hull allowed the traditional radial layout of command hulls to be retained.

More important than these tactical advantages were functional advantages. As was shown with the Wasp class, warp field geometry would have been awkward if a spherical hull with its relatively large frontal area had been used. The discoid hull was also found to channel warp field flow across its upper surface towards the bussard ram scoops of the warp nacelles. This channeling effect improved field efficiency at all power levels and speeds. As the understanding of warp field mechanics was refined, the trend towards saucer-shaped primary hulls would be intensified in later Starfleet vessels.

In most respects, the Moskva class continued design and engineering trends established in the Comet and Daedalus classes introduced at the end of the Romulan War. As in these classes, ship functions were clearly divided between a command/crew hull and an engineering/propulsion hull. The bridge was returned to its customary position atop the command hull and the shuttlecraft bay was again placed in the secondary hull. The fusion reactor was centered along the longitudinal axis of the ship, and impulse thrust ports exited immediately in front of the warp bustle detachment seam.

Weaponry was the then-standard mix of fusion-warhead missiles and lasers. New to this class was an early type of ultraphased pulse laser cannon, two of which were mounted in the chin of the primary hull. Although the on-target energy output of this new weapon approached that of early phasers, its power requirement was higher and its range was substantially less. However, subsequent refinements lead to steady improvement and, ultimately, to the development of true phasers in 2202. Although Moskva -class ships were the first to be fitted with phasers in 2204, lasers were still carried by the Moskva class and later classes until the 2220s. Finally, warp capability was supplied by the long-awaited Hiryu mark III drive units.

The first ship of the new class, USS  Moskva (NCC-374), entered service with Starfleet in April 2179. An additional 30 ships (NCC-375 to NCC-404) joined the fleet through 2183. Moskva -class ships gained immediate popularity with officers and crews. First, total laser firepower was increased some 75% over that in the preceding Wasp class. Second, because the ship's mass was more equally distributed along the longitudinal axis than in the Wasp class, Moskva was significantly more maneuverable at both sublight and warp speeds. Finally, the more warp-dynamic design allowed greater cruising and maximum speeds.

The Moskva class had an outstanding safety record. No ships were lost because of mechanical failures. However, an incident occurred aboard USS  Johannesburg in 2186 when a faulty nacelle flow monitor falsely indicated a runaway positive feedback power loop within the plasma flow governor. Believing that a catastrophic warp core explosion was imminent, Chief Engineer Roberta Bocharnikov ordered the warp nacelles and warp bustle to be separated. Although unnecessary, these maneuvers were successful in causing the separated warp core to initiate its automatic shut-down routine. The warp core, nacelles, and the rest of the ship were towed to Starbase 13, where they were successfully re-mated. Despite her supreme embarrassment, Bocharnikov oversaw the reassembly and relaunching of Johannesburg and retained her position as chief engineer.

Although most ships of the Moskva class had left front-line service by 2215, some continued to serve as auxiliaries and training vessels until the 2240s. After retirement from active duty, Moskva -class ships were used as testbeds for many emerging technologies owing to the similarities of their layouts to those of succeeding classes. USS  Moskva was the site of the first successful ship-to-surface transport of a Human being in 2206, and USS  Gato was the first ship to fire photon torpedoes in 2214. In addition, Taurus -class tugs, which entered service in 2182, and Sanford -class repair tenders, which entered service in 2185, were derived from the Moskva class and used the same primary hull and warp drive assembly.

The Moskva -class cruiser USS  Aurora (NCC-377), a participant of the Battle of Eohippus IV, is on display at the Starfleet Museum.

Standard displacement: 67,750 t

Crew complement: 160 (27 officers + 133 crew) Weapons: 8 Type VI laser turrets (8 × 1 mounts), 2 Type VII laser cannons (fixed mounts), 2 missile launchers with 36 Spartak missiles Embarked craft: 4 medium cargo/personnel shuttlecraft, 2 light personnel shuttlecraft, 5 fighter/scouts Warp drive: SSWR-V-A spherical cavity M/AM reactor with 2 Hiryu III nacelles Velocity: wf 4.0, cruise; wf 5.0, supercruise; wf 5.2, maximum Units commissioned: 31