Quote:
Originally Posted by Blue_Heron
. . . Do you know if it had the four stringer system, or the two box stringers? If I remember correctly, they made the transition in '71 or '72.
I agree with Denny that removing the inner liner from the hull sides reduces the stiffness. But the hull bottom, deck, and stringers should act together to create a diaphram type beam that's pretty stiff by itself, so I wonder if there isn't something else going on as well. For the diaphram to bend enough to crack at the keel, I would think the gunwales would have to bow out a LOT. Is that what's happening? Is there any separation at the joint between the deck and the hull sides?
Dave
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Dave, my '72 is a 4-stringer hull, so I'd guess this boat also had 4-stringers. I think Potter made the switch in '73 or '74. The first 2 stringer hull I have seen was a '73, but there may be some fuzz on the year the boats were actually produced, since the year on the title is when they were sold.
You're right about the deck bonded to the top of the stringers creating one hell of a large stiff I-beam or diaphragm. If the new deck wasn't well bonded to the top of the stringers, that would significantly reduce the stiffness of the "assembly", especially in torsion, so that's something that should be looked at during the "autopsy" of this failure. I also agree that there is probably a lot of distress at the hull/deck joint. Yacht surveyor Dave Pasco mention deck joint distress as being very common on boats with structural hull failures. Rub rails are often attached to that joint with tapping screws, which don't hold well if there is relative motion between mating parts, because the sharp threads act like knives that cut into the glass.