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Practice repair hull next steps?


I have finished with the bottom repairs. The gel coat needs some more practice and I had issues with cold temps. I had the glass repairs too high along with some oddities because this hull was repainted poorly at one time. The paint is thick and wavy in places along with large areas of droopy paint with runs. I am not taking that all down and repainting. So it is white where I did repairs and as level as I dare take it. That was my gauge of success for this part of the project.
so now I flipped it over. I pulled the forward inspection port to make hole just large enough to get my arm in. I noted that the port side deck where the drill is in the picture had a lot of movement. The reason is the foam block on that side loose and slide more to the center of the hull and so there is no support from the foam. I also removed the wood backer block for the cleat that was pushed through. So the cleat is an easy fix for me. Reach in sand and put some new glass on it. Then taper edges and glass the hole. Then glue up the wood and install the cleat. I can shove the foam back in place but I don’t think I can get a glue on it too and bottom. I am wondering if some expansion foam wiiid hold it ok. I might be able to get a couple of dabs of like 5200 on the top and bottom. So what are the thoughts for holding the foam in place through the existing hole in the deck?




Well-Known Member
The factory used huge amounts of yellowish expanding foam because Styrofoam is too fragile to hold at too-few spots. :oops:

The rainless summer kept me sailing, so I didn't have a chance to use the gray Pond-and-Stone variety of Great Stuff foam I'd already bought for the purpose. :confused:

I'd tip the boat up on its side, use a rubber hammer, and drive the target Styrofoam block as far forward and to one side as possible. Pour a 2-part foam, or spray the above Great Stuff top and bottom of the block. It's not just floatation, it's also structural. Sunfish Styrofoam blocks tend to get compacted from heavy deck use and heavy weather from underneath, so be generous within the manufacturer's limitations.

Try searching this forum, using the word "expanding". Much research on Sunfish Styrofoam blocks has already been done here. :cool:


Active Member
The brown polyurethane wood glue that looks like pancake syrup will hold it if you put a few beads of glue on the foam block and close it up overnight. The dampness in the foam will make the glue setup and fill the voids.

Breeze Bender

Breeze Bender
I used the 2-part expanding foam from US Composites. I haven’t seen much posted about gorilla glue as an option, but if it has been used successfully I’d try that route. It would be cheaper and probably easier. Eddie_E, did you just tilt the boat and pour the syrup?


Active Member
It's very easy to do, just remember it will expand to 3 times the volume you put down. Moisture helps the expansion while curing. I wouldn't add any water in a Sunfish though. The damp air in most Sunfish hulls is more than enough moisture to expand and cure the glue. in addition to using this on Sunfish, I used to fly radio controlled airplane combat and we used this method to bond wooden spars to Coroplast wing skins and the bond would often survive 30 mph impacts.