First post...Bought 1999 Vanguard Sunfish for $300...

Thread starter #21
Great I will get a 2 qt kit of 6# foam from JD ...Its funny all the damage the boat had and the foam is like new still glued in and white and dry...I'll tell you a story about foam... I had a sunfish that I had done a lot of work to I sailed it for a year or so ,then I decided to put some foam under the cockpit. I bought some foam called great stuff from the hardware and put it under the cockpit man that stuff was some "great stuff" it worked fine for a while and then the unthinkable happened ??? What might that be? After the foam had been in there for 6 months working fine....It got wet and expanded like a balloon ...really a balloon. The cockpit was pushed up a good 3 inches in the middle Imagine the horror looking at it...well to fix it I had to cut an inspection plate in the middle or the floor and dig out the "great stuff" and put weights in the floor for a few weeks to get it flat again... I guess I could have read the instructions where it says "spray with water to make the foam expand more...Well that was fun.


Active Member
No kidding! I never had that problem and I always had water in the hull. I wonder what
I did different. Maybe I didn't use as much foam as you did. I injected it through holes
in the cockpit floor and did not use a lot because I was worried about the problem you
described. When the foam activated it oozed back out the holes in the floor.
Thread starter #23
Oh yea I probably used a lot of it...what happened is it had an uncured "bubble "inside the foam and when water got to it it ballooned I use only polyurethane foam made for boats no worries because it fully cures in minutes...and if under the cockpit just expands out around the confined area...

signal charlie

Well-Known Member
Staff member
The foam bonding under the tub is usually in 6-8 very small blobs, about silver dollar size. Their locations can be spotted a lot of times on the bottom of the hull because stress risers form in the gelcoat over those hard spots. So a very small amount of foam is needed, and leave room for it to expand. Less foam means less trapped water. I would make sure to leave plenty of areas for water to flow through in case a leak developed, make sure water can get out to wherever your chosen drain point is. For us we like to use the deck drain or put in a center deck inspection port, lots of access there to take care of backer block issues, daggerboard trunk repairs and sponge out any small leaks.