Multihull Seaworthiness

this article was published in MULTIHULLS MAGAZINE in 2002 and was also featured in the SAILORS MULTIHULL GUIDE published in 2003

by Gregor Tarjan

The question of Seaworthiness:  Design and Construction.

A brief analysis of the most important considerations when purchasing a cruising multihull.

 
Team Phillipps

Safety and seaworthiness, as Czeslav A. Marchais describes it in his great book “ Seaworthiness - the Forgotten Factor” should be one of the most important considerations when shopping for a boat. There will be many parameters to consider when buying a particular cruising multihull, ranging from price, looks, to how many she sleeps, but none should be weighted as heavily as seaworthiness. Generally speaking a seaworthy boat is one that has been expertly designed, constructed, and can show an impeccable safety record.

Even though most of us might be coastal sailors the concept of seaworthiness is as important for someone who is about to start a family circumnavigation, as well as for someone who is a coastal cruiser or sails in “protective” bodies of water. Believe me, the Great Lakes, shallow Long Island Sound or Chesapeake Bay can get very nasty indeed. Even coastal sailors, attempting a “hop” to the Caribbean or Bermuda, better be ready to face the worst the ocean can dish up. The highest waves on our planet were measured in the Gulf Stream, not 300 miles from shore. We all know that where the Continental Shelf begins and the waters get shallow near the coast, waves become unstable and tend to break earlier. Consequently it is not a surprise that experienced sailors tend to feel much safer offshore than close to land. Most of us are costal cruisers, nevertheless the consideration of a tested, proven and seaworthy boat should be as important as for someone who ventures offshore.

Seaworthiness means different things to different people, but most will agree on following definition: The way the hulls at varying payloads move through the water, the ability to handle waves comfortably and safely at varying points of sail and lastly weathering storms and bringing ship and crew back to land unharmed. Well designed and built multihulls are one of the safest vessels afloat and in most cases it is human error that poses any danger to crew and boat. By human I also mean the builder, which also necessitates a close analysis of the boat yard and construction parameters. As can be imagined, a well designed vessel in experienced hands can still be a suicide machine if it as been slapped together quickly or as in many recent cases of high tech construction failures, has been built by inexperienced, cheap labor under a mismanaged conditions. If one has a lemon, one is lucky if only ports will leak or one might experience areas of delamination of foam cored hulls. In the worst cases the boat might break apart in the most horrendous of circumstances. As we all know, catastrophes don’t happen when its blowing 15 knots under clear blue skies. Therefore, when shopping for a boat, the question of construction should be on the very top of the list. 

An Outremer catamaran beating to weather

 Construction: Lets briefly look at the past, at the era before multihull mass production. The acceptance of multihulls in the 60’s and 70’s suffered tremendously by the homebuilt boats of that time. Plywood and fiberglass, still excellent materials today, were the norm then. Even though these had an even greater forgiveness to building inconsistencies than today’s high tech composites, enough ill-constructed multihulls were built to give them a bad image. Many beautiful Pivers and Searunners, which were excellent designs for their time still exist. Nevertheless I would guess an equal number of them, which were irresponsibly manufactured, simply rotted away at their mooring or fell apart giving the early US multihull movement a bad start. In some extreme cases people even lost their lives due to badly constructed multihulls. One of the early production catamarans, maybe even the first ones that came from molds, were the great Telstars trimarans and the Iroquois catamaran of the 70’s. These British built vessels, were mass produced in great numbers under controlled conditions and many are still sailing today. My friend purchased one recently and I had the opportunity to measure the heavy scantlings of the hull.  If one can live with the narrow overall beam, the overbuilt and simple, production built Iroquois is in my mind still one of the best bargains around. On the other hand, the legendary Wharram cats must be mentioned. They were mostly homebuilt by amateurs, and represent the simple Polynesian concept of a safe, seaworthy boat. 1000’s are sailing today and can be found in every part of the world. I even spotted one in Nepal !

 A recent upwind sail on a new 47’ production catamaran reminded me of the importance of construction and builder experience. The boat was built by a production builder, who built narrow, heavy cruising cats of a different design. The rig on this boat was recently tuned and all shrouds and mast stays were properly tensioned. Nevertheless the leeward shroud in these brisk conditions was extremely loose and was whipping through an arc of almost 2’! Not only did this represent a serious injury risk for the crew, risk fatigue of mast fittings and create an inefficient upwind rig, but more importantly, also showed the excessive flexibility of the entire structure. The boat would cycle through this athwatship flex every 2 second and over the years would eventually do serious damage to its entire sandwich structure. 

Today’s composite materials allow multihulls to excel as lightweight and strong structures in an often quite hostile environment, the ocean. But that also comes with a price. High tech sandwich lay-up and construction must be performed in an absolutely controlled environment. Factors such as resin and lay-up ratios, temperature, humidity and pressure are crucial to the strength of the final product and leave no room for any deviations. Hence: A seaworthy boat is only as good as its construction. Yard reputation. is as important as its product

  Design: The design of a boat is a beautiful science. Theoretical, practical and intuitive factors are fed into a complex design spiral weighed by compromises, which are constantly and repeatedly changed, updated and interactively fine tuned until designer and client decide to stop and declare the result: “ The Final Compromise or The Boat ”. Good sea boats evolve not only from this theoretical design process, but also by constantly improving and changing the actual vessel. Often the rig, underwater appendages or even parts of the hull are modified to achieve this. Usually if you see at least a dozen vessels of the same design you could assume that they are good boats. But if you know that a 100 of them were built over decades, heard or read about them in numerous international magazines or tests, it is almost a guarantee of a good design. The final confirmation of seaworthiness is when one discovers that a design, built in great numbers has traveled to the most remote locations of the world.  

The definition and discussion of seaworthiness and good design are complex and mean different things to different people. Even different size boats will have to be analyzed using different parameters. A 22’ Tremolino, designed by Dick Newick is a beautiful little trimaran and will be a safe boat to use in a protected bay or even for a day sail along the coast. More experienced sailors will think it even safe to venture offshore with her. Taken to the extreme, we all know the French will not stop of taking anything across the Atlantic, but I think this is a different story, possibly of Latin heroism. That is why designers will usually start with parameters such as overall length, payload, the operating environment, and principal purpose of the boat.  A 32’ cat with the same design parameters, and operating environment as a 50’ cat probably will have a lesser degree of safety factors simply because of her shorter length and narrower beam. Although the smaller vessel in experienced hands might come through rough conditions as safely as the 50’ cat, it will not be as comfortable or “felt” as safe as the larger vessel. Which brings me to following universal truth of sailing, performance and safety: At sea, given equal design and operating parameters: size counts more than anything else, and I mean waterline length. This is why a longer multihull with narrow hulls, will usually be a faster, safer and more seaworthy boat than a shorter one with the same weight.

There is a famous misconception about the relationship of the overall beam of a multihull and its dynamic stability. As my friend and experienced multihull sailor, Matthieu Rougevin-Baville explains: by narrowing the hulls one actually increases the axis width, which is the only interesting width in a catamaran. Having the same overall beam a multihull with fatter hulls actually has a narrower axis beetween hulls. The diagonal distance is the most important criteria, the longer the hulls and the narrower they are, the longer diagonal axis we have...and the more stable the vessel becomes.” Having said that it will become clear that most larger multihulls come to a sudden stop by going front over end. ..…not over their beam ends. They actually trip over their leewared bow, especially if they are fine and low in volume.

 Outremer 45: One of 142 vessels sailing the world’s oceans

 Following example will show that even great designers and builders can produce unseaworthy boats if they are working in unfamiliar territory. Lets take for instance Team Phillips, the 125’ monster cat designed for the tough, nonstop around the world Race. This boat got me fooled, because I considered her a stunning breakthrough which might have worked. She was designed by one of the most experienced British multihull designers Adrian Thompson. It can certainly be argued that the radical rig and hull would or would never have worked. Apparently the computer models and analyses of past experience said they would have, but at the end it was a disastrous failure, which almost cost the crew their life. The designer, although immensely qualified, never tackled anything of the nature of Team Phillips. On the other hand projects such as Team Phillips are invaluable to the multihull community and in a larger sense humanity might still be sitting in caves, if there weren’t heroes, adventurers and visionaries around who would push the envelope. Above example should remind us that the chances of a good design are so much higher if it was born from a mind that has done similar designs. Experience is invaluable in the world of boat design. Catamarans are as different from trimarans as monos are to multis. Taken to the extreme, lets say a famous monohull designer would design his very first cruising multihull. I would not want to be the first customer of that boat.

             Different boats,   different principles. When I worked with Dave Pedrick in 1984’ on Dennis Conner’s legendary Americas Cup 12 metre “Stars & Stripes”, he always reminded me : “If it does not break, its too heavy” ! In the same year I participated in the Star Boat North American Championship, in which Dennis Conner’s margin of beating most of the fleet was not only a result of the smallest detail improvements and modifications to his boat but also product of his immense experience. Again we see: it is the familiarity, skill and know-how in a particular field that produces winners. 

At sea even a 64’ Outremer looks small

If you are in the market for a cruising multihull, take the aspect of seaworthiness very seriously. The brutality of the sea is often forgotten at boat shows or when studying the glossy brochures. In the age of technology, gadgets and globalization boating is safer than ever. Nevertheless the issue of seaworthiness of multihulls, with their higher speeds and loads should be a top consideration, even for a coastal cruiser. Designer experience and a reputable yard are as important as an impeccable safety record of a particular design. Do your homework. Read all the books you can find on multihulls, talk to surveyors, authors, delivery skippers and designers. Chances are, they will confuse you with different opinions. The bottom line is: Sail as many different boats as possible in as heavy conditions as you dare. Common sense will do the rest.

Gregor Tarjan, is a yacht designer and president of Aeroyacht Ltd, the Exclusive US distributor for Outremer, the legendary French built, high performance cruising catamarans. He is also the US agent for CATANA and  St.Francis luxury cruising catamarans. For more information, please visit the very informative website: www.Aeroyacht.com

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