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post #29 of Old 02-18-2009 Thread Starter
Join Date: Feb 2009
Location: Cromwell CT
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Thanks to everyone for the really informative posts. I had a retired surveyor friend read through these to help me sort them out. Here's his take on it all.

Regarding the hull slamming and oil canning: All boats slam to some extent when pounding to windward in waves, and whether one pounds worse than another is a very subjective matter. Can't really be measured. Of course, the larger boats won't jump around as much as the smaller ones (you know, mass and inertia and all of that), plus when you're getting spray in your face you build up a strong negative psycholgical feeling. Naval architects can usually evaluate the pounding propensity of one forebody shape over another, but almost all hull shapes are a compromise of sorts to meet the need for interior space and accomodations. High speed power boats have deep vee-bottoms to minimize the pounding, at the cost of added HP requirements. Even the America's Cup boats, long and skinny, have to accept some pounding and discomfort in trade for overall speed in differing conditions. Most boat builders are always experimenting with hull designs, but inevitably reduce the analysis to a "seat of the pants" determination. And rest assured that every manufacturer will claim that this new design is much better.

On oil canning, many owners mistake some deck flexibility for oil canning, when in reality they're describing a deck problem from delamination, sometimes calling it a trampoline in bad cases. Also, in a seaway, many lightly built boats will flex noticeably, and this, too, could be called oil canning by an untrained person. That kind of flexing almost always causes hairline crazing or cracks in the surfaces of gelcoat, particularly in the "sharp" corners or where the molded shape changes greatly. The term "oil canning" originated when motor oil was sold in quart cans where the top could be easily popped in and would pop out when you took your finger off. Sort of a pucker. And similar to what you'd see on a can of food that has gone bad, where the top has a slight dome that you can pucker.
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