fiberglass and waterproof wood glue

You just won't find me using any PVA based adhesive on something going on the sea..... I'd rather have the boat stay in one piece, than disintegrate beneath me...

Try the test suggested by PAR, then retry your hammer test.

 

Yeah, without a solid base line and real tests, breaking stuff and taking a guess how it faired isn't the wishest approuch. Immersion is the true test for PVA's and a simple fish scale on test pieces can tell you a lot.

 

I hear you guys and appreciate the info, but no water is getting to these seams. That said, there is not enough rigidity unless I use double layers. It's more time consuming than cutting the 1/2 by 1/2" strips and screw/gluing them in. I am sticking with what I did on the first build and just using the strips/glue/screws.

For what it's worth, I remove all the screws except the ones I use to fasten the deck. I'm also going back to Loctite Poly Seam Seal for all the fastening instead of Max Elmer's. It does not pull free from the ply like Elmer's does.

The first yak I built (pics here when I joined) saw hours and hours on the water, and a lot of rough water in the Gulf. It was actually 1.4lbs lighter when I cut it up than when it was completed. It's was waterproof.