TOPIC: Fiberglass repair

I have a quarter size hole in the hull of my 1968 Corson. It is just below water line and goes thru hull. I cannot get to the underside to support a patch from the inside without cutting into the deck floor. This wil be my first attempt at fiberglass repair and I have watched a number of videos and read the sections on here for instructions (very informative) but every one I've seen shows a support on the underside for the layers. Any suggestions?

Well, if there id enough room ? Take a plastic milk bottle, cut the shape larger than the hole. Poke a hole in the center of the plastic shape.
Put a piece of string through the hole, tied to small washer on the back side. Cut some matt the shape of the plastic, needle and thread the edges of the matt to the plastic.
Soak the matt with mixed resin, and push the plastic plug through the hole and pull the string to hold the plug flush to the inside of the hull. I would think the plastic is flexible enough to push thru ?
It will be pretty much a toggle bolt, but round ?
Let cure, cut off string, and you now have a backer for glassing the outside
This is all I can think of ?

Make a hole in a scrap piece of wood same shape, to test the theory ?

Chuck- Very clever- what does evryone else think about this- or is their a another way.

Kinda the old sheet rock patch/repair trick, good thinking Chuck! I was thinking stuff wadded up newspaper, plastic scouring pad, or something in there - but I like your idea better.

Chuck you read my mind, do it again, do it again! LOL That's exactly what i was thinking, just like Mark said the old hole in the dry wall repair trick.

Bob

Sounds like a winning idea to me. Give the man a cigar.

ACtually, Chucks method is used all the time in fiberglass repair. Usually it's done by making the backer piece out of 2 - 3 layers of scrap pieces of CSM cut to about 1 1/2" larger than the hole and coated with resin. You use your fingers to sand the inside as best as possible with 60 grit and then acetone wash it. Mix up some thickened resin and then insert the "String" Patch coated with the gooped up resin and pull it tight. Use a bondo spreader to smooth out the thickened resin and the hole is pretty much fixed. You can sand it down and lay a couple more layers of CSM on the outside and mix up some fairing material using some glass bubbles and you'll be good to go.

As I said this will be my first attempt at fiberglass repair so excuse my ignorance of CSM- what is it?

Chopped Strand Mat = Less strength than cloth, but better surface contact (smoother)/adhesion, and better "water proofing" qualities.

In terms of the finishing- after I set the mat/cloth/mat and fairing filler do I just use white gel coat for the finish?

Yes, mix up some gelcoat and thicken it with some cabosil. Leave your fairing a bit concave to allow for the gelcoat paste to do the final filling and that way youi can sand the gelcoat to the final level. Sand to 100 grit then buff and polish and she'll be good as new.