Hull stress crack repair?

[MartyH]

I am working on my SJ21 MkII # 1593. Where the hull meets the forward lower corners of the storage area under the v-berth, there are obvious spider cracks with approximately 1/2 inch diameter circular marks in the middle of the spider cracks. I think this is a pretty common area for stress cracks and I am wondering if any of you would weigh in with suggestions for making repairs. I have received a couple of suggestions locally and I am just looking for the most used method.

s/ Marty

[Mark Sailmaker]

The corners of the box are stress concentrators. If you cut the lower corners out of the box, you can reinforce the cracks from the inside. Add some 6" deck plates near the corners in the bunk top for access, fill the cutaway with foam and reglass inside and out and you will regain the integrity without the "hot spot". With the hull reinforced from the inside, the outside can be a much more cosmetic repair. All repairs should be made with epoxy since polyester is unreliable for secondary bond repairs. Epoxy also is compatible with styrofoam, so common blueboard foam insulation is cheap and easy to find. Ideally, all the edges of the liner parts should have been landed on foam before they were glassed to the hull, but that's not what happened....

[MartyH]

Mark, thanks for the reply. You're the first person to recommend foam in the reinforcement process. Are the bottom corners glassed to the hull? Can I make a very controlled plunge cut and lift the corners out, or is grinding required? Again, I appreciate your help.

[Mark Sailmaker]

Marty - Sorry to be so late replying...hope you haven't been waiting for me. My thought for cutting out the corners is a 2" or so hole saw with the barrel laid flat on the hull so that the round hole cut out is cut thru the vertical sides of the anchor box. I've also heard of people cutting a 1" slot all the way around the box, cutting the whole box loose from the hull, grinding the hull smooth, reinforce the hull as necessary, filling the gap with tapered foam and glassing on both sides over the foam. That will definitely eliminate the hard spots.