Multihull Madness

Tracing the evolution of the modern multihull.

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Some say that markets afford a true test of a products value, if so, then boat shows are a great place to test the waters. Over the last two decades, in-water show attendees have noticed how catamarans and trimarans have taken over more and more slip space. Apparently, a growing number of boat buyers are convinced that two or three hulls are better than one. Skeptics still question whether this is a case of design breakthrough or more an example of a marketing success. We think its probably a good dose of each, and its time to take a close look at whats really driving this multihull mania.

Polynesian voyaging catamaran Hokule

Advocates tout the advantage of a lead-less approach to sailing: the boats seldom heel, won't sink, and offer a spacious deckhouse with a million-dollar view. Performance-oriented multihull fans lean toward a less voluminous approach. Their favorite ultralight designs deliver a sports cars acceleration and represent the epitome of shoal-draft cruising. Proponents remind single-hull sailors that when you put a multihull on a reach in 12 or 20 knots of breeze-all but the kite boarders and motor boaters are left astern. Despite all this keen optimism, dyed-in-the-wool monohull advocates still have a few reservations. So in Part I of our multihull report we look at the design evolution and how we arrived at where we are today.

Leopard catamarans

Background

Multihull voyaging has a well-documented history that includes Polynesians traversing Oceania, Micronesians voyaging the western basin of the Pacific and Indonesians coast-hopping from Papua, New Guinea to Sumatra aboard their gossamer jukung outrigger canoes. In light air, there was always more paddling than sailing, and the risk of a squall-instigated capsize was mitigated by small sail area and inherent weakness of organic sails and coconut-fiber rigging, which, like a fuse in an electrical circuit, broke or tore before the boat could capsize.

The shoal-draft nature of these vessels favored beach launching and scooching over reef-strewn shoals. A tropical climate lessened the need forbelowdeckaccommodations and a mandate to provide shelter from hypothermia. In short, the vessel design resonated with its use.

Leopard catamarans

Today, the Polynesian Voyaging Society (PVS) and the Bishop museum continue to add data and carry out valuable research. Whats clear is that the double-hull voyaging canoes of Oceania provided connectivity among the archipelagoes scattered from Easter Island to New Zealand. In full trim, these 60- to 70-foot LOA voyaging canoes displaced about 25,000 pounds and relied as much on able paddlers as they did their scant 500- to 600-square-foot sail plans. With a relatively small beam compared to modern multihull design standards, these 17- to 18-foot wide twin hulls did not have the righting arm of a modern catamaran. In heavy weather the spars were lowered to the deck and a basket-like drogue device could be streamed astern.

Leopard catamarans

Leopard catamarans

In 1975, the Society launched Hokulea-a replica of a traditional voyaging canoe. Although the FRP hulls and modern lines and sailcloth used in the replica were far from what early Polynesians worked with, the Hawaiians made up for material substitution with years worth of authentic voyaging. They replicated passages made by their forebears, and at the moment, theyre finishing up a two-year west about voyage around the world.

Herreshoffs Amaryllis

Multihulls first came to attention in North America when Nat Herreshoff designed the catamaran Amaryllis and won the New York Centennial Regatta in 1876. This began a long-standing yachting tradition of establishing rules to sideline multihulls, and effectively close the door to cats and tris.

For nearly a century there has been intense controversy over where multihulls fit in inshore and offshore racing. Fleets of one-design speedsters from Hobies to Farrier/Corsairs have had great success with their own regattas, and today theres even growing success in the effort to include multihulls in epic offshore races such as the Transpac (multihulls welcome) and the Newport to Bermuda Race (a decision is in the offing). The multihull-friendly Americas Cup, now more drag race than tactical skirmish, speaks for itself, and some of the around-the-world and trans-oceanic records have been set by multihulls.

While racers now happily claim multihulls as their own, the cruising community was where multihull acceptance first took hold. For decades, there was much more of a warm welcome for cats, tris, and even an occasional proa among coastal and ocean cruisers. It all began in a backyard experimental era that gave rise to big mistakes and great strides forward.

Arthur Piver a pilot, sailor, author and print shop owner in Mill Valley, CA probably deserves the title-patriarch of the modern multihull. He sold an idea as well as plans for his easy to build tri-hull designs. These DIY plywood boat building projects were inextricably lashed to dreams of tradewind adventures. His acolytes had a wide range of boatbuilding and seamanship skills, and not surprisingly, outcomes tended to favor better built boats and capable crews.

In Pivers wake, came some better designs and engineering. Jim Brown and Norm Cross, also west coast designers, took three hulls to the next level. Brown refined the approach to glass-over-ply construction and dubbed his slant on voyaging Seasteading. A Brit named James Wharram favored a more traditional Polynesian hull design for his DIY catamarans. They sported a short hoist, square-headed sail plan because Wharram had a penchant for favoring capsize avoidance over light-air performance.

During this era of innovation, an avid multihull aficionado once said that ferro-cement monohulls were the best thing that ever happened to multihulls! Asked for clarification, he went on to say that the appeal of boats spawned from a truck-load of wet cement drew the attention and allegiance of most of the wingnut, home-builders previously obsessed with multihulls.

Dave Martin’s 30-foot Polynesian-inspired Tiki catamaran

With little publicity and even less marketing effort, the DIY followers of Piver, Brown, and Wharram set off in homebuilt boats headed towardfar flung points around the world. The debate over whether these multihull prototypes lived up to the pitches made by their proponents lives on, but one thing is quite clear, there were noferro-cement sailboats at any of last years boat shows, but the multihulls continue to flourish.

Multihull pioneer Tony Smith

Backyard to Factory

Todays multihulls are a far cry from what Piver or King Kamehameha observed at Waikiki. The DIY era of the 60s gave rise to inputs from designers like John Letcher, Dick Newick, Nigel Irens, Ian Farrier and many others. Builders like Tony Smith, who started molding 26-foot Telstars in England in the early 70s and moved the company to Annapolis, Maryland where the business evolved into Gemini cruising catamarans, are emblematic of the launch of production built cats and tris. The stage was set to go global and Prout, Lagoon, Fountaine Pajot, and dozens of others set up shop.

This evolution came with taller rigs, high-modulus sail cloth and rigging to cope with more than the maximum loads generated by a vessels righting moment (righting arm x the vessels displacement). More power in the sail plan meant that when an unanticipated big gust erupts from a mediocre looking squall line, the crew had to be ready to dump the traveler and/or mainsheet, and in some cases ease jib sheets to spill more breeze.

If these steps were not taken, the heeling moment could overwhelm the righting moment and a capsize become likely. Without ballast and a low center of gravity (CG), theres very little secondary righting moment. The limit of positive stability (LPS, the point at which the boat will no longer right itself) reaches zero at around 80 degrees, having peaked somewhere between 10 to 25 degrees. In contrast, a seaworthy monohull has a much smaller righting arm and less initial stability but benefits from a secondary righting moment from the ballast. This shifts the limit of positive stability to 125 degrees or more (common for many offshore racers and cruisers).

The multihulls approach to staying upright is dominated by its beam and the buoyancy of each hull. The vessels wide stance, weight of the windward hull, and the buoyancy of the leeward hull defines its reluctance to heel. This also governs how efficiently the energy derived from the sail plan can be utilized. The advantage of this huge reluctance to heel, results in more lift and drive from a given amount of sail area. The problem with this approach to carrying sail, is that heel, a familiar warning sign of being over canvased, no longer affords an early warning.

The traditional monohull signals that a reef or two is needed when it submerges its rail or the helmsman has to fight the boats tendency to broach. The monohulls stability safety valve is its willingness to heel away and recover from a rail-plunging, boom-dragging, masthead-dunking, knockdown. But with multihulls, theres a very fine line between starting to heel and being unable to stop the rotation toward capsize.

To better understand the full implication of heeling moment, one must recognize that wind velocity increases arithmetically, but pressure on the sails increases exponentially. For example, we say that when a ten-knot breeze builds to 20 knots, the velocity has doubled. However, in the same scenario, the pressure on the sail is defined by the square of the original velocity (10 = 10 x 10 = 100). This 10-fold increase in pressure results in a huge energy transfer between sails and hull. Rig loads spike and the heeling moment increases.

At most risk are racing multihulls that have even taller rigs and greater sail area-to-displacement ratios. This makes them both faster and more vulnerable to capsize if the crew loses focus. The role of a skilled skipper and crew is paramount-at times the mainsail trimmer is the most important person on the boat. He or she becomes the failsafe when it comes to coping with the unexpected gust. And in many cases, the traveler, with its lengthy port-to-starboard, radial-shaped track is the best friend of those trying to depowering the mainsail.

trailerable Telstar

trailerable Telstar

Preventing capsize

One of the biggest decisions a multihull cruising sailor has to make is how much sail area to carry. The more like a race boat their cruiser becomes, the more demanding the sailing challenges become.

Normally, modern multihulls handle an average breeze with a full main and a fairly small jib (in relation to mainsail size). Its all thats needed to keep things rolling along. High-performance multihulls are so fast that the apparent wind moves forward, and even when sailing a deep reach, the breeze is on the beam and sails are trimmed to the apparent wind.

If the vessel starts to heel or bury the leeward ama, it slows down and the apparent wind velocity decreases, causing the apparent wind direction to shift aft. This causes the sail plan to be over-trimmed and increases the heeling moment, just when its least desirable. To complicate things even further, the pathway to a sheet or traveler no longer involves crossing a span of flat deck. A large, unanticipated, increase in heel can cause the crew perched on the windward ama to be more involved in holding on than reaching for the offending traveler control or sheet.

Competitive multihull crews know that they cant weather a knock down-and so, sailing on the edge means maintaining a near-instantaneous ability to depower through the release of traveler and sheet controls. When this becomes a 24/7 obsession, one thing is certain, its no way to go cruising. This is why most cruising multihull designers have taken a different tack.

Cruising multihull designers hedge their anti-capsize bet with a less aggressive, lower sail area/displacement ratio sail plan and higher volume, increased freeboard, and more buoyant hulls. This approach works to lessen the likelihood of turning upside down, but it doesnt make the risk completely disappear. One of the risks facing shorthanded multihull cruising stems from long night watches and the efficiency and reliability of todays autopilots.

Watch-keeping in a main saloon with 360 degree visibility meets the International Regulations for Preventing Collisions at Sea (COLREGs) requirements, but it puts the person on watch too far away from the sheets and traveler and insulates them from telltale signs of changing weather. Little things like a sudden puff of cold air on a hot sticky night can signify the onslaught of a thunderstorms downburst. Its often a subtle, 30-second prelude to an approaching maelstrom, but with someone at the ready it can be time enough to ease the sheets and take over the helm.

There have been enough multihull capsizes over the last few decades to draw some formal attention. In the late 1990s, the University of Southampton, Wolfson Unit in the United Kingdom conducted a naval architecture multihull capsize study that began with a review of historical data. They compiled a series of reports on 124 capsize incidents that occurred over a 30-year period.

The study included 33 cats, 67 tris, 2 proas and 22 reports listed only as multihull. The survey indicated that catamarans incidents seem to be more wind induced while trimarans were more vulnerable to wave impacts. The tank test follow ups in Phase II were aided by Naval Architect Alex Simonis, and the study revealed some useful insights into trends and how hull shape, volume and weight affect vessel behavior. As expected, beam played a pivotal role in righting moment and lowering the vertical center of gravity (VCG) also improved the righting moment and limit of positive stability. Keels seemed to slightly increase capsize vulnerability by preventing the cat from sliding sideways when impacted by a breaking wave.

During tank testing, the center of effort (CE) of the sailplan was varied during the dynamic testing. Increasing the height of the CE correlated with increased chance of pitchpoling, so did increased displacement and moving the longitudinal center of gravity (LCG) forward. Smaller, less buoyant amas (floats) on trimarans were linked to a higher risk of capsize as were trimarans with their mass situated along the centerline of the middle hull. This early work focused on causes of capsize beyond wind heeling moments and gave designers a starting point from which to develop faster or more stable multihulls. However, designing an un-ballasted sailboat that is both fast and stable remains a challenge to be met.

A Closer Look: Catamarans

Catamarans are generally more weight-sensitive than monohulls, so achieving maximum strength for minimum structure becomes much more important. A favorable strength/weight ratio is particularly critical among shorter-waterline boats (40 feet or less), because cramming the usual creature comforts of cruising into two short hulls can hamper windward performance significantly.

This photographic tour of the builders in Cape Town, South Africa, offers a glimpse of the challenges of building a cruising catamaran—whether it is for full-time cruising or to meet the very different demands of the Caribbean bareboat charter trade.

1. Building each hull in halves makes sense in tight quarters, but the centerline joint must be bulletproof.
2. An obvious structural hot spot in catamaran building is the cross-beam area near the bow, where the two hulls are joined.
3. Using knitted Kevlar to reinforce the crossbeam can raise a couple of issues: The fabric’s different structural properties creates a new hot spot, and you must rely on secondary (post-cure) bonds at the joint.
4. Minor mistakes when measuring molds can lead to big problems when trying to align the hull and deck.
5. The pelican striker (aka prodder or seagull striker) and crossbeam work together to counteract headstay loads. This critical work best is handled by spar fabrication specialists.
6. As in a monohull, bulkheads are often a hot spot for structural loads. Any bonding here requires special attention.

Darrell Nicholson, editor of Practical Sailor, grew up boating on Miami’s Biscayne Bay on everything from prams to Morgan ketches. Two years out of Emory University, after a brief stint as a sportswriter, he set out from Miami aboard a 60-year-old wooden William Atkin ketch named Tosca. For 10 years, he and writer-photographer Theresa Gibbons explored the Caribbean, crossed the Pacific, and cruised Southeast Asia aboard Tosca, working along the way as journalists and documenting their adventures for various travel and sailing publications, including Cruising World, Sail, Sailing, Cruising Helmsman, and Sailing World. Upon his return to land life, Darrell became the associate editor, then senior editor at Cruising World magazine, where he worked for five years. Before taking on the editor’s position at Practical Sailor, Darrell was the editor of Offshore magazine, a boating-lifestyle magazine serving the New England area. Darrell has won multiple awards from Boating Writer’s International, including the Monk Farnham award for editorial excellence. He holds a U.S. Coast Guard 100-ton Master license and has worked as a harbor pilot and skippered a variety of commercial charter boats.

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