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Trimaran capsizes off New Zealand! Multi-hull or Mono-hull?

Navigation/ Weather Forecasting/ Charts/Computers/Anchoring/Safety

Are multi hulled sailboats (trimarans and catamarans) as seaworthy as monohulls?

Depends (comment)
Total votes : 37

Multihull Safety

by sandy daugherty » Fri Apr 11, 2008 3:06 pm

Escape hatches are required by law in the CE. Thats why you see them on many cats. Their desireability is open to question.

Before I retired from the NTSB I had the oportunity to study the complete Coast Guard database of boating accidents and Summary
Data of proprietary actuarial information from sources within the Lloyds' Groups, with a focus on vessels with accomodations including permanent berths, head(s) and galley. I tried to exclude beach cats and tris, and daysailers by excluding boats under 24 feet. The data was not user-friendly and required a lot of external correlation because many vessels were incorrectly classified. That ultimately prevented releasing any conclusions because GI+MGI=GO (garbage in plus more garbage in still equals garbage out.) This was also a problem with the older NTSB databases that included pre-digital-age reporting. However, I discovered in the process that there were few differences between monohul and multihull rates of occurrence. That's easy to understand; human error trumps mechanical failure and design deficiency evermore. Here are some of the facts that did become apparent: Vessels designed for racing and record attempts break. Vessels built for cruising don't break. People who race drive themselves and their vessels to the limit. [please forgive the pun] Cruisers drive their homes to the next nice place.
The rates of actual vessel loss (outside of competition) remained the same for monohulls and multihulls, over many years, with catamarans emerging slightly ahead of other vessels in the last years of available data. Reports of large numbers of catamaran roll-overs are probably anecdotal as accident statistics reveal a (slight) decline, with a slight increase in sinkings among monohulls. There was a lot of confusion in the data between catamarans and trimarans, which I can only suggest an interpretation for:

Vessels purpose built for competition are not recorded as such. Each accident had to be researched individually. Many were not insured, meaning that Insurance data would not take them into account. In fact, Many sinkings of monohulls were extremely difficult to document because they were never widely reported. This is changing as news media is becoming more interested, especially in colorful visuals.

A very small percentage of trimarans are sold for cruising, as a very small percentage of catamarans are sold for racing. The best correlation between racing and competition vessels was a ratio of lwl to mast height.

Where I was able to distinguish between cruising and competition vessels, I found that the rate of personal injuries and single fatalities was higher among monohulls. That should merit further study because those injuries appeared to occur in better weather conditions, not in worse. These accidents included cabin injuries, man-overboards, and deck injuries such as inadvertant jibes.

My conclusions were impaired by the quality of data, and my proposal of a National Transportation Safety Board Special Study was properly overshadowed by more important issues. But there is enough factual data to prove that cruising multihulls are no more, and possible less dangerous than cruising monohulls in all reported conditions of weather, traffic, and human frailty, regardless of location.
sandy daugherty
Posts: 40
Joined: Mon Apr 07, 2008 3:44 pm
Location: Annapolis

Cats vs Monos

by Arni » Sat Apr 19, 2008 10:06 am

First, to correct an earlier post, escape hatches are NOT mandatory for CE certification. My Manta 42 is CE certified and does not have them.
It is not reasonable to look at racing boats to compare safety. Both racing Cats and racing monos are pushing the envelope, both in the way they are designed and built and in the way they are sailed.
Cruising cats truly are harder to capsize than cruising monos, generally speaking, as they have no, or little, keel to trip over. Thus if caught on the beam by a breaking wave, they have a chance of sliding and not capsizing. The Wolfston Unit at Southampton University have demonstrated that there isn't a monohull built that will resist capsize if the wave height is 70% of their length, and it might take a wave only 30% of their length to capsize some. Tests on catamarans show that they may avoid capsize when hit by much larger waves, but a lot depends on the design.
When underway, the biggest danger to a cat is stuffing one of the hulls into a wave when the stern is not directly pointed at the wind. The rapid slowing pushes the apparent wind way up, and the subsequent broach may turn into a pitchpole. Unless you are an expert helmsman with a very well designed cat, you should not run in severe seas. But proper tactics and design, just as in monohulls, make a cruising cat just as safe, and, IMHO, sometimes safer. Insurance statistics for cruisers back this up.
To suggest they are only safe for coastal cruising is nonsense. Prout, of UK, built around 4000 cats before they went bankrupt 8 years ago. These vessels completed a huge number of ocean voyages with an excellent safety record. I don't believe I have ever heard of one capsizing. Prouts were conservative, and not appreciably faster than a monohull, but they were certainly just as safe, and apart from speed, they did have the other advantages of cats; Interior volume, shallow draft for example.
Steve Dashew has made a career out of designing longer, narrower sailboats which only need a modest rig to attain good passage speeds. He's done it again with his motor cruiser. What he doesn't realise is that what he has been working towards all along is a catamaran. We have narrow, easily driven hulls with high hull speed, and on a cruising boat only need a modest rig to maintain good speeds.
You want to watch a Sharkcat playing in the surf off an Australian beach and then say cats aren't as seaworthy!
Yacht Jade
Posts: 37
Joined: Mon Mar 24, 2008 8:55 am
Location: Cruising Pacific

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