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Old 05-03-2015, 08:03 AM   #97
brian eiland
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City: St Augustine, FL
Country: USA & Thailand
Vessel Name: RunningTide
Vessel Model: 37 Louisiane catamaran
Join Date: Jul 2013
Posts: 883

Perhaps a litle research is in order here. Lock Crowther did some rather extensive tank testing of the capsize question with multihulls a number of years ago at the Southampton Univ wave tank. I think the results will surprise many.

Multihull Capsize Prevention <split> - Page 12 - Boat Design Forums

Can't seem to find the exact posting I was looking for, but here is one I made

It's a shame we could not get ahold of that video Derek Kelsall mentioned in his posting, excerpt... "However, imagining lying ahull to those waves did not fit the picture. A couple of clients have described being in a situation where they expected to capsize from the size of the wave and the angle of heel, but then suddenly found the cat was back on its feet again. One of these clients decribed the waves passing while lying ahull and of the most disturbing part being the fall of the windward hull into the trough as the wave passed. The video demonstrated the situation as I understand it. The tank test was done in Southampton comparing a Lock Crowther catamaran ferry with a comparable mono, in large breaking waves and high wind, with the models lying ahull. As the wave hit the cat, which was still in the water, the windward hull was thrown up into the air, looking like an immediate capsize, but before the angle of heel had gone to 30 - 40 degrees, the wave had passed to the lee hull, lifting it just as rapidly to bring the cat level and then fall as the wave passed. The cat never capsized. The mono rolled every time. This situation actually applies whatever the orientation of the catamaran to the waves.
Monohull verses Multihull powersailers / motorsailers [Archive] - Boat Design Forums

Note: reference source, Lock Crowther Designs

"This work (tank testing at Southampton Univ) has indicated that the well designed catamaran is remarkably safe in breaking waves up to considerable height, even when beam on, we were unable to capsize a power catamaran yacht in the largest wave which could be generated. This corresponded to a 52' wave for a catamaran of 40' beam. Scaling this down to a typical 24' beam cruising cat means she should be O.K. in a 31' breaking beam sea. An equivalent size mono-hull power boat was easily capsized by a 25' breaking sea, and in tests with conventional yachts after the Fastnet disaster, it was found that a 40' mono-hull yacht could capsized in a 12' breaking sea"
Multihulls in 70' Waves Multihulls and 70' waves [Archive] - Boat Design Forums
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