: say that the problem is strained fiberglass caused by excessive deflection
: of the deck, probably caused by pushing off on the deck to get out of or
: into the boat and/or heavy cargo on the deck. They said that the problem
: can be prevented by making sure that there is adequate reinforcement on
: the underside of the deck by way of extra fiberglass, a bulkhead, or a
: reinforced strut connected to a bulkhead. He said that it was unlikely
: that the type of glue used to bond the strips contributed to the problem.

The only time I've seen this issue on any of my boats was when I filled 2 feet of an end compartment with two-part urethane flotation foam. As an experiment I stripped and glassed a kayak as one piece (ie the deck to the hull were formed together with no post-mating). I used the urethane foam in the two ends where I couldn't sand the wood smooth and put glass. In the end it actually made a nice, solid kayak, but that's a whole other story. The foam expanded so much it stressed the the composite lamination at the glue joints. I ended up with the same white stress lines at the glue joints.

My $0.02 for what it's worth...
Dan