Multihulls in Heavy Weather

Hello! The subject of Multihulls vs. Monohulls is a hot one, and is likely to continue to be. 🙂 However, there is one designer who has put online a very good paper on multihull seaworthiness. It is, of course, true that he is a catamaran designer, so the criticism may be the paper is biased, but it is very technical in nature, and I find (having an engineering background) reasonably complete and suited to the informed lay reader.

The article on your site I am referring to is: Multihulls.

John Shuttleworth’s article on multihull seaworthiness is here:

I believe that your opinions may be swayed by his treatment. As always, seaworthiness is as much a function of the crew as of the boat, but a good crew with a bad boat can only go so far. I was very timid about the idea of multihulls and blue water, but decided I would research it before making up my mind. What I found were many good sources of experience reports (MultiHull Voyaging by Thomas Firth Jones for example) which finally convinced me that multihulls, designed correctly, could be as seaworthy in blue water as a well designed monohull, if not more so.

I have heard a bit about storm tactics and multihulls, and the one thing I have heard that I do not know if you have mentioned (not having purchased your book yet) is using a large para sea anchor. I am told that using a very large para anchor, head-to the seas, creates a slick much like the one one gets with a keel boat that is properly hove-to. The idea is to use the para anchor at roughly a one wavelength distance from the boat. This saps the waves power as it comes towards the boat and will then rarely, if ever, break across the bow. Since swell cannot capsize a boat, it stands to reason that this would be a very good tactic.. a sort of heaving-to for a multihull. The para anchor should be something like at least 75% of the beam. I have heard that 28 foot, nylon para anchors are most common, being able to be gotten from other sources than custom. Have you heard of this tactic?—Timothy

Hi Timothy: Multihulls in heavy weather is a controversial subject. We cover this topic exhaustively in “Surviving the Storm” including some unbelievable photos of a cat in the Queen’s Birthday Storm–and the answers are complex.

From my perspective as someone who has sailed quite a few miles in cats, as well as monohulls, and from the research we’ve done I feel the following:

1)Size is a major issue with multihulls in heavy weather, much more so than with monohulls.
2)All other things being equal, multihulls take better seamanship than monohulls for a successful outcome in heavy weather (this includes weather analysis, tactics, and boat handling).
3)The major ingredient in multihull safety is understanding weather, and having the speed to get out of the way of bad conditions. However, speed and the cruising multihull is typically an oxymoron. The vast majority of cruising multi’s are overweight, under-rigged, and have too little wing clearance.
4)Most of today’s multihulls are optimized for space and convenience, with chartering being the driving force. These are good boats for what they are designed for, i.e. short hops in protected waters. But they are not designed for heavy weather. Just take a look at the cockpit doors on most cruising cats.

As to your comments on para anchors, you will find quite a bit of data on this subject in the above mentioned book. Para anchors can work, but in survival storms, with large breaking seas, they have their problems with both mono- and multihulls. They are not a magic bullet (we have seen no evidence about the “slick” you mention).

Finally, as to your comment on crews and boats in heavy weather, I take exactly the opposite view. A good crew will usually do well in terrible weather by virtue of their skills, even in a less-than-optimum boat. On the other hand, there are literally dozens of examples of sailors heading offshore in good boats, with the latest gear, getting into serious trouble precisely because they have not taken the time to learn and practice fundamental heavy weather seamanship. Regards–Steve Dashew

Posted by Steve Dashew  (November 30, 1999)

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