Filling a gap on fiberglass 420 sailboat deck

[Canracer]

Oh man, is the boat in an unlit garage Those pictures...

You can patch those cracks. A Dremel is probably too small. You will want clean fiberglass on each side of the crack to make for a strong patch. A power sander or maybe a flap disk on an angle grinder would take care of things fast.

 

[Canracer]

That air channel is probably there to stiffen the cockpit. You think the whole hull was full of water and then it froze? That's a lot of water. Or maybe some water pooled in the cockpit and froze (makes more sense.) Did you just buy this boat?

 

[Sean Kelly]

I was thinking water trapped in the air channel because the delamination was the worst on the border of it. Would 4 or 5 layers of 6oz fiberglass cloth be structurally sufficient? I used a Dremel to open up these cracks.

 

[Sean Kelly]

Also, for the size of the gaps would it make sense to buy a gallon of epoxy?

 

[PAR]

Epoxy stores well and you'll likely need more later. 6 ounce is fine, though you'll need more layers to bulk it up. Use the mini disk grinder on the Dremel and make a shallow concave path along each crack, maybe a 1/2" wide on either side of them. Grind down through the gelcoat and feather it out as best as you can.