Fiberglass repair

I’m in the middle of refurbishing a Phantom sailboat (very similar to Sunfish). I’ve reattached a separating hull/deck with marine-tex and the repair went very well, but the 5-min set sure goes fast!

Next I put in an inspection port to get a look at the inside of some hull damage. I was pleased to find that the crack did not go the whole way through. The damage is not visible on the inside but outside is about 2 inches on the side wrapping over to about 1 inch on the bottom. I’m planning to grind away the damage plus a couple inches around the damage and repair with a layer of glass and epoxy resin. (I understand that I won’t be able to gelcoat over top) The hull is so thin that I can only imagine getting 1 layer of woven glass. Is that enough?

Also, I’ve read that epoxy resin is harder to sand than typical fiberglass resin, but some brands are easier than others. Can anyone recommend a brand that is good for providing a good sandable surface? I'm hoping to use the same resin to fill in some scratches on the bottom. For now I don’t plan to paint the hull so I don’t need the fix to be too pretty, but I hope to paint in the future and I want to be able to get a reasonable looking fix. I want to sand the fixes flush with the old surface, but I'm worried about the epoxy beind harder than the gelcoat and having trouble tapering the fix in.

I have some books on fiberglass repair that have been very helpful, but they are focused on larger boats. I just need a reality check on repairs to a thinner hull. There seems to be less margin for error!

I found the inside of the boat to be very dry. The water I drained out of the split lip must have just been rain water. I did find some broken styrofoam though. It is attached to the top and bottom, but split in the middle in places. Does anyone have experience with this fix? I’m thinking of getting some of the expanding foam used to attach the blocking and try to do the fix with that. Does that make sense?
 
From the Sunfish Sailors Clonefish guide, Howmar Boats, Inc. of Edison, NJ was the original builder. J-Point Marine of Rumford, ME bought the molds when Howmar went out of business. They might have some information - http://www.j-pointmarine.com

Hull - Deck joints are usually rebonded with laminating resin which would have given you more working time.

When you start your repairs my experience is the thin hull doesn't respond well to a grinder. It can remove a lot of material fast making a small job into a large one. Small sanders and hand tools or a Dremel are better choices.
James Town Dist. is a good place to lookup repair materials and their handling requirements. http://www.jamestowndistributors.com
West System Epoxy has a guide for gelcoat over epoxy - http://www.westsystem.com/frames/tier1/home.htm
Epoxy, pre-mixed filler A-B type in tubes or laminating depending on the job is a good repair material in general, but is not always the best choice. For scratches not down into the glass fiber gelcoat could be better. Same for busted out gelcoat where the glass underneath is ok. You could build it up with polyester or epoxy resin and mix in some colloidal silica. Don't fill the ding quite to the surface and finish it off with gelcoat. You can sand and rub out gelcoat to a nearly flawless blend. Gelcoat will stick to polyester resin better. You could just fill with white Marine-tex epoxy putty and get a close match.
 
Dan - thank you for the links - I will check them out.

My research so far has shown that epoxy resin makes for a better and stronger fix. The only negative I've seen is that it can't be gelcoated over. It is an old boat and I'm not too concerned what it looks like below the waterline, so the gelcoat is not an issue. Also, my understanding is that regelcoating the entire boat is time consuming and expensive. I suspect that the value of this boat would not warrant that. If I want to make the hull look better some day I would most likely paint.

But I have no actual personal experience. Are there other reasons to use polyester over epoxy?
 
Gelcoat is just polyester resin with a lot of colorant. Epoxy can be gelcoated over, but requires an extra step and may chip or blister in the long run as you will read in the West System guide. I suggested polyester as a repair media for simplicity. In my opinion the strength factor for a small cosmetic repair is negligible and polyester resin will cost half as much.

It sounds like what’s needed is to chip away the cracked and loose gelcoat and sand down a small area surrounding the surface split. So long as the glass fabric below is undamaged no lay up of extra fabric should be needed. If it were the lions share of reinforcement would be backing laid up on the inside. For filling out the surface a little resin to rebond and seal the exposed fabric is all that’s needed. The rest is just replacing the cosmetic shell. You could do the whole thing with gelcoat alone if the fabric is ok. What ever you choose, sanding will be about the same for any of the materials.

Rather than speculate further why don’t you peel away the broken gelcoat and see what you have to deal with.
 
Just chipping away the damage and patching with gelcoat seems like a simple but great idea. I could even lay up an extra layer of glass over the inside to give it a tad more strength in case some of the glass was damaged. Thank you for the great time saving advice! As they say... "KISS - Keep It Simple Stupid"!
 
um.... don't just grab hold of the easiest thing to do. The type of damage will tell you what you need to do. Without pictures I can only speculate.
 
I'll chip the damage out and attach some pictures (inside and out) this weekend. What you said makes sense though. The heavy glass weave I can see from the inside looks fine. With the thickness of the hull there can't be too much damage on the outside. A gelcoat seal on the outside and another layer of glass on the inside - where I don't need to worry if my first glass job is pretty or not - should be stronger than new.

I just cut the broken springs off the trailer that came free with this free boat, so the boat is not going anywhere soon. I have a bit of trailer repair to do in addition to the boat repair. I quick gob of marine-tex won't get me sailing so I'm going to try to do the fix right.
 

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