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What’s the worst that can happen?


So long and short is I recently starting sailing my ‘78 sunfish which I purchased for $350 complete with an extra set of spars. I had her out 4 or 5 times. Well needless to say I’m really enjoying myself, but I noticed the foam blocks are loose and deteriorated. Actually when I look in the hull there are plenty of little styrofoam balls covering the interior.
So my question is am I causing any damage sailing her this way?



Active Member
As you noticed there are no bulkheads so the blocks provide
hull support and stiffness. First thing likely from extra hull flexing
will be popping the hull seams amidships. You may also get
oil-canning of the hull bottom. Sunfish are kind of a project boat
as most are serving long beyond their expected lifespan. As much
fun to fix as to sail I say.


Upside down?
Staff member
I wouldn't worry about this considering that you paid very little for a 40-year old boat. Fixing the internal polystyrene structure is a major job. In the meantime, just enjoy your new hobby.
BTW, does the deck flex when pushed?

signal charlie

Well-Known Member
Staff member
Tap the blocks back in place with a rubber mallet and tack them down with small blobs of Great Stuff pond foam. Go sail another 40 years. We had one boat with No foam and she sailed great. Not sure how the seams would react to that long term.


Well-Known Member
Is there an object inside (rolling around) and doing the damage?

Tilt the Sunfish on edge, and proceed as above.


I don’t believe there anything other then the foam blocks rolling/bouncing around causing them to crumble.

Is there any difference in the pond foam besides the black color?
I have access to closed cell expanding foam from work, thought I’d use that unless there is something better.

Eventually I’ll vacuum out as much of the mess as I can and foam the blocks back in place. Thanks for the suggestions.
As for now I’ll sail her the way she sits.
Not many days left before the weather changes.

signal charlie

Well-Known Member
Staff member
They market the pond foam as being more water resistant, but any of those type foams will absorb water if left submersed. The black does look better in a pond.

Closed cell is the way to go, Marine Grade if you can find it, which I believe is a little more resistant to fuels and oils. Two brands we have used and liked are TotalBoat and Fibreglast.

Enjoy your mess abouts, thanks for posting the pics!


I can tell you, it (the contagion) gets worse! :confused:
You can say that again! I now have three. My first, A well used ‘71 that I picked up three years ago and updated the rudder to the ‘new’ style with the help from Alan G. The second, a ‘69 with some fiberglass damage that I intended to use just for parts but am tempted now to try to repair. Lastly, a beautiful race ready 77 that I bought a few weeks ago from Greg on this forum. I’ve been teaching my wife to sail and we thought it would be nice to have two boats out at the same time. Unfortunately, the season has closed in around us here in Michigan and I will have to wait til the spring to take the “fleet“ out.