Design Dynamics

Open Bridgedeck Catamaran

Configuration & Basic Types

Amultihull, just as any other type of boat, presents a series of compromises, and this applies to overall hull, deck and configuration as well. Concessions often have to be made because of space, performance or construction costs. In addition, the intended usage will be a significant factor in determining the shape and size of the vessel. Successful cruising designs will balance all parameters and only you, as a sailor, will know which type of catamaran will be suitable for your needs.

A monohull's characteristics, largely determined by the beam-to-length ratio of the hull and its displacement, will vary very little from another ballasted boat, as there is only so much volume you can fit into a single hull. This will establish the amount of accommodations, which will not greatly differ from one monohull to another, setting a stark contrast to a catamaran, where intended parameters vary so much more.

Basically, we can break down the major design considerations into: overall configuration,

If one thinks of an open bridgedeck-type of catamaran, images of Hobie Cats on one end of the spectrum, and giant-open ocean racing multihulls on the extreme end, come to mind. They have no fixed coachhouse roof and some of them, especially the small beach cats, only have nets strung between the hulls. Larger examples have partial composite platforms, which stiffen the structure and allow for cockpit seats and helm stations. Since without a solid coachhouse there is less boat to build, these multihulls will be generally lighter and have better aerodynamic properties than full bridgedeck-type cats.

Although few manufacturers and designers have attempted to build open bridgedeck catamarans for cruising, only the most die-hard campers will find them useful for liveaboard applications. Typical examples are the older MacGregor 36, Stiletto 27 and 30, the French KL27 and Corneel designs, which could be sailed hard by lifting a hull (something that you try to avoid when cruising with a fully decked-out boat). Some of these vessels even featured a tiny removable doghouse which provided some shelter for the crew. On smaller open bridgedeck multihulls the only living quarters are found in the confines of the hulls. Even on larger types, they are cramped and not conducive to long-term cruising. The advantages of these sporty vessels,

Copyright © 2006, 2008 by Gregor Tarjan. Click here for terms of use.

Basic Catamaran Configurations

Corneel Catamaran

especially in sizes below 30 feet, is their lower cost, trailerability and lively performance. However, attention has to be paid that they not be overloaded or else one could easily turn a cat into a t they are big moneymakers and are considered the workhorses of the sea.

A large exception to the class 1 type of configuration is found in sizes above 30 feet, which could be considered as class 2. Manufacturers such as Maine Cat and a few other custom multihulls such as the Shuttleworth successfully combine an open-deck plan with a certain degree of cruising comfort. In order to provide some shelter for the crew, large semi-rigid biminis are erected. Not only are these afterthoughts unsightly and do no justice to the beauty of these boats, but they also add a considerable amount of drag, contradicting the nature of these athletic multihulls.

Large charter boats or "Day Boats," as they are called, also utilize the open bridgedeck layout to maximize cockpit space. These machines can entertain up to 80 passengers and are found in holiday resorts around the world. Correctly managed and marketed,

Partial Bridgedeck Catamaran

These are often referred to as cruising/ racing types and, unfortunately, very few existing manufacturers still make them. Designs such as the older Edel and Outremer catamarans had a rigid deck and a small coachhouse, which was completely separate from the hulls. My own Outremer 43 "Flo" was of that category. She was a great sailboat and provided ample room for our family cruises along the U.S. East Coast. Similar to the class 1 vessels, the bridge decks of these types of catamarans are also shorter fore and aft, and the accommodations are simple.

Partial bridgedeck catamarans usually place simple sitting arrangements and nav-stations on the main deck. The balance of the layout, below The Broadblue range of cruising catamarans are examples of full-length bridgedeck multihulls, providing plenty of volume for cruisers.

Catamarans Design

cruisers.

Shuttleworth Catamaran

above The Blubay 72 is a state-of-the-art, maxi-sized racer-cruiser featuring a separate saloon pod. She will cruise at close to 28 knots.

below The Gemini 105Mc, seen here in the Patagonian channels, is a popular full bridgedeck catamaran which, in capable hands, can be taken to the world's most remote areas.

such as the galley, heads and berths are often situated in the hulls. Most of the time, these multihulls only have sitting or crouching headroom in the saloon, unless the cabin sole is dropped significantly, compromising the underwing clearance. The Edel 35 was particularly notorious for her low bridge deck, although hundreds of them were built.

Edel Open Deck

Advantages are good looks and light weight overall structure, but the fact that one can only access the hull compartments via the cockpit poses limitations for serious cruising or live-aboard applications.

Some years ago when Outremer was looking for a substitute for its 40 footer, I was asked to design an open bridgedeck type and came up with a compact 38' racer/cruiser with low profile and tiller steering. Unfortunately, lack of demand prevented the project from being realized and the Outremer 42 was born. However, I feel that a properly designed class 2 multihull is a fantastic compromise for the average weekend sailor. It is unfortunate that presently no manufacturer builds one.

Bridgedeck Catamaran

Probably the majority of production and custom cruising catamarans belong to this category, which is the focus of this book. A bridgedeck multihull maximizes the use of space and features a solid deck with a coachhouse that spans the entire width of the cockpit. There is one main entrance into the boat via large sliding doors, and access into both hulls is through companionways leading down from either side of the large saloon. Bridgedeck catamarans are ideal for cruisers or liveaboard sailors. These vessels feature ample payload-carrying capacity and provide good protection for the crew. Helm locations are usually behind the coach roof bulkhead or in some rare cases on the aft end of the hulls behind the cockpit.

These class 3 multihulls contain all the comforts of home and feature a spacious

Catamarans Design

saloon, galley, and navigation station on the main deck. The coachhouse acts as a centralized core, spanning both hulls, which are usually reserved for heads, sleeping cabins and storage. Unlike any other type of boat, monohull and multihull combined, the class 3 cruising catamaran has an unrivalled "homey" feel to it. The wide cockpits are protected by biminis which integrate seamlessly into the coachroof. This not only looks good but creates an inside-outside space that is both practical and unique.

Large bridgedeck cats have the capacity and volume to carry most of the items you would find in your home. From dishwashers to the generators that power them, you can actually have it all. However, the desire to load up too much sometimes overburdens the vessel, compromising its performance.

On vessels larger than 40 feet, headroom is sufficient, although individuals 6 feet and taller might have to make compromises in the forward part of the saloon or in the extremities of the hulls. Designers try to balance the need for ample bridgedeck clearance and place the cabin sole high enough to avoid underwing pounding created by waves. Low, good-looking silhouettes can be found on larger catamarans, although some manufacturers have the "no holds barred" approach and make their boats look like a toolbox. Although this maximizes space, the chunky appearance is detrimental to the performance of the boat as it increases air drag. Finally, square coachhouses make catamarans look rather unattractive.

Some builders elect to pull the solid bridge deck all the way from bow to stern.

above This recently launched Yapluka 72' catamaran is seen here in full cruising trim and serves her owner-couple as a liveaboard world voyager and mobile office.

Bridgedeck pounding caused by waves is one of the drawbacks of low underwing catamarans. Moderate displacement, full-volume bow and stern sections, and a high and long bridgedeck will minimize, if not eliminate, annoying wave slap under the saloon sole. Although bridgedeck height is a very important parameter, it is a misconception that it is the only design feature to look for. One has to consider weight as well as its distribution and support by the hulls, especially in the extremities. Heavy, low bridgedeck multihulls might make great liveaboard vessels, but they should only be taken to sea by masochists.

below A partial bridgedeck cat, such as the older Outremer 43, was a swift boat but had the disadvantage of separate saloon and hull access.

Parameters Contributing to Bridgedeck Pounding

This book would not be complete without the mention of the new breed of luxury yacht: the Multihull Supercat. These magnificent vessels usually measure in

Multihull Boat Plans Free

This is beneficial for stiffening the structure and making the most out of the available deck space. The Gemini catamaran is a very successful design which employs this layout. Yet designers who try to put too much weight into the ends must be careful. These types frequently suffer from excessive pitching in a seaway and display mediocre performance under sail.

Superyacht Catamaran

This book would not be complete without the mention of the new breed of luxury yacht: the Multihull Supercat. These magnificent vessels usually measure in excess of 100' and can sail on free wind energy at more than 30 knots without any heel. They feature living rooms the size as found on monohull superyachts twice their size, and require neither a dozen crew to run them nor large diesel engines. Very few builders in the world specialize in these types of vessels, yet their ideal application as large eco-expedition vessels, corporate entertainment platforms, or ultimate private yachts is unquestionable. Blubay Yachts of France seems to be on the forefront of this group as they have gained invaluable experience by being the only builder that has built a succession of composite superyacht multihulls upwards of 100'.

The world market for extravagant pleasure boats has been steadily growing, yet the catamaran platform for luxury sailing vessels has only recently been recognized.

Modern composite materials and highlevel engineering utilizing Finite Element Analysis now permit the construction of large structures such as multihulls, which was not possible 10 or 20 years ago. The aeronautical and automobile racing industry have contributed considerably to the design and engineering of complex composite structures from which super-catamarans have greatly benefited. The use of aluminum has been the classic hull and superstructure material for large vessels around 60' and it is still a strong and economical build alternative. With the advance of composite technology experienced builders (usually French yards) are developing lighter, stronger and increasingly sophisticated super-yachts, providing clients alternatives that were unheard of just years ago.

Large catamarans, with their wide and stable platforms are becoming recognized as ideal structures for lavish, as well as exciting, pleasure boats. Their vast living accommodations and privacy layout make them ideal for people looking for an alternative to deep draft and heavy monohulls. In addition, their low-profile underbodies permit access to shallow harbors. The new generation of research vessels and oceanographic laboratory ships are frequently large catamarans. They project the image of eco-friendliness and efficiency as they are propelled by clean wind energy. Their shallow draft allows access to reefs and remote anchorages. Their wide aft platforms provide superior storage facilities for large dive tenders and even ideal helicopter landing pads. The demand for these types of superyacht catamarans worldwide is steadily growing.

below Large luxury yachts, such as this 100' catamaran, can easily accommodate several dozens of guests in ultimate comfort while, at the same time, they can sail at double-digit speeds. With world oil prices steadily rising, they very well might become the new breed of mega-yacht.

Mega Catamaran YachtsSailcraft Cherokee Catamaran
Boating Secrets Uncovered

Boating Secrets Uncovered

If you're wanting to learn about boating. Then this may be the most important letter you'll ever read! You Are Going To Get An In-Depth Look At One Of The Most Remarkable Boating Guides There Is Available On The Market Today. It doesn't matter if you are just for the first time looking into going boating, this boating guide will get you on the right track to a fun filled experience.

Get My Free Ebook


Post a comment