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Originally Posted by afishin82
ok did some research and form what i could tell it seams if i leave an air gap between the hull laminate and bulkheads it should fix the hard spot issue. i assume this is true because the glass used to tab them in will flex with the hull  . u think that would help? U cant see in the pics but i cut out the lowest corners of the bulkheads so water will drain to the bilge. |
Yes, the air gap would eliminate the hard spot issue. However I think gravity + capillary action might cause resin to wick out of any cloth spanning the gap, so it would help to fill the gap with something soft to prevent that. I believe cabosil is a little too hard for that, but any type of caulk that provided a large radius fillet to support the glass would work.
The purpose of the bulkheads is to tie the stringers together to provide lateral support, which prevents them from buckling while also adding a lot of torsional stiffness to the structure. This would be particularly important if the stringers were tall thin 1x12's with a large difference between their "stiffwise" and "easywise" bending resistance. (bending about the respective horizontal and vertical axes.) However your stringers are ~2 inches wide at the top and probably 2.5-3" wide at the bottom, so they're already pretty stiff in both directions. Simply tying all 4 of them together at the top, combined with the robust tabbing of the stringers into the bottom laminate, has proven to create a very stiff and torsionally rigid structure that doesn't really need bulkheads.
After thinking about the changes you've made to that hull, I've concluded that it won't have nearly as much torsional stiffness
above the deck as the original Seafari had with it's cabin top and bulkhead that tied the hull sides and gunnels together, nor will it have the bending stiffness provided by the tall cockpit coaming. Therefore any extra torsional stiffness provided by the under deck bulkheads is a good thing! More robust tabbing of them to the bottom with 2 layers of 1708 would also improve torsional stiffness; taper the tabbing so top layer is a little shorter than the first one. That horizontal rib about halfway up the hull sides will make a handy shelf, but it adds virtually none of the torsional stiffness that you'd get from adding a core to the hull sides. You could maximize the overall torsional and bending stiffness of what you have at this point by building a cap with wide gunnels, a thick core, a large front deck, and a wide full transom cap. Some vertical ribs/rod holders to tie that horizontal shelf to the deck and gunnel would also add a little more bending stiffness to the hull, although it probably won't do much for torsional stiffness.