Gary,

Phill has some great techniques for the laminate and core repair. The break sounds typical of a catamaran hull failure though. A compression failure in the hull just forward of the front cross bar. A-cats are very light and not designed for the loads that would come from a sloop bridal forestay set up. Composites are very poor in compression. Carbon is one of the worst fibers for this as well, mainly because you use carbon to go light, giving very thin skins to your hull laminate. Thickness is the key to good compression resistance.

Given that the A cat probably was able to get away with not having to have a false floor as described earlier, you could most likely add the additional reinforcement needed to comensate for the added compression loads on the deck alone. Bonding an additional layer of core to the existing deck, then laminating and fairing the new top surface would drastically improve the comression taking ability and if done with the same skill shown in your other work, you would not be able to tell anything was done. This would be a lot easier than opening up the unbroken hull to place a sub floor.

Just a thought, Good luck in getting back on the water soon.

Matt