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Old 12-07-2012, 12:20 PM   #42
Tad Roberts
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City: Flattop Islands
Vessel Name: Blackfish
Vessel Model: custom
Join Date: Dec 2012
Posts: 724
Quote:
Originally Posted by manyboats View Post

Very interesting about the % of length capsize studies. As stated it says the longer a vessel is the less likely it will capsize from a given wave (in height).
Well Tad I'll be watch'in out for those 17' waves while out in my 30' boat. Only been in those once and I was in an 28' OB that I designed and built. Mus'ta done someth'in right as I'm still here. Actually I'll be watch'in out for for those 9 footers too. AND I'll be hang'in on white knuckl'ed to the helm also.
Does the % of length "rule" or findings take into consideration the CG change over long boats and short boats that are all the same size ... volume/disp ? Or are all the hypothetical short and long boats all the same beam? Or have I read this all wrong?
Those studies were done on "average" (whatever that is)hull models. The economics of most reseach means you use models borrowed from other studies. We can assume average types of hulls with typical length/beam/freeboard/depth. And the work was done with whatever waves that particular tank was capabile of generating, which may mean little in the real world.....

Which brings up another factor...keel tripping. Many folks have written about this and it's been studied a bit, again in test tanks. One theory is that as a wave passes under a boat, the keel (if there is one) holds the bottom back while the breaking top pushes the hull to leeward, increasing roll. Proponents of shallow draft boats cite this as a danger and claim a hull with no external keel will just slide over the wave with no "tripping".

Thus, perhaps, according to this theory, a deeper draft heavy displacement hull might be more prone to capsize (by wave action) than a lightweight shallow draft one.......
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