Bill,
I am not sure I follow you. These beveled inserts match the bevel in the large machined aluminum backing plate (that was nicely corroded from contact with water and the stainless insert). The image above is of the side contacting the overhead. The opposite side has the mating bevels for the nut inserts. If there is any advantage to this arrangement with this backing plate it is that it makes for a little less chance of braining yourself on something protruding from the overhead because it is essentially flush.
I think the original hardware arrangement can be made to work OK, but with dual sized holes through the core and some Duralac on the insert to stop the corrosion. For sure the high strength core I will use would likely solve much of this problem anyway. I'm not sure what the compressive strength of this core is, but you could hit it with a hammer and not dent it. I would also expect it to be more thermally stable making the sealant work much better and longer.
After completing the core and skin work my plan would be to use the aluminum backing plate as the drill guide, but only letting the 1/2" bit penetrate about 5/8". Then use the center of that hole to drill the rest of the way through with the 5/16" bit. I may do some testing with a small scrap piece of this core to see if it would be even helpful to oversize drill and then refill with CS. I suspect that It wouldn't make much difference. This core already has glass layers bonded to it on both sides, so with the added layers in the repair glass (inner and outer skins) I have to believe the screw will have much more solid glass to bear against under the shear loading.
It is a good thing to have a brother in the high end boat building business, so you can mooch crazy expensive scraps like this core. It also makes you aware that as much as I am spending rebuilding this old boat, it pales in comparison to new boats.
Aspen Power Catamarans
