A 1/4" crack is DEEP. Could it be that the gelcoat that was used to paint 
out the interior of the boat pooled in that area to a depth of 1/4"?  Get 
some light and dig around and you should be able to tell if it;s gel coat or 
glass.  There shouldn't be any filler material there; we simply prewet the 
plywood and bonded one side, and when that cured we bonded the other side. 
Bonds should be a bit wetter than a laminate but definately not wet enought 
to be swimming in resin, which becomes brittle and dead weight.

I don't suppose you're anywhere near Sacramento?

jerry