advice on fiberglass repair below the waterline

I just bought a powerboat that has some damage on the bottom. I was told the boat broke loose from a dock and bounced up and down near the shore on rocky bottom. Not sure if this was the case or they hit someting underway. Either way I have the boat and I am trying to fix it.

Attached is a picture of the damaged section. The boat has a keel (skeg) with a srtaight inboard. The damage starts where the skeg (keel) begins and goes back about 4'. No other part of the bottom has any damage, just on the skeg. Below is procedures how i was going to fix it please let me know if you have any suggestions on how i plan to fix it. I have done glass work on old wood work boats but that is it (new decks, building cabins). Any advice is greatly appreciated.

1. Remove botom paint about 10" past each side of the damaged areas. Sand the gelcoat off to get to raw fiberglass material. Do I have to sand the gelcoat off to get new fiberglass to adhere correctly or will it adhere to gelcoat?

2. I am going to use US composite 635 med epoxy (I have some left over from another job). I was going to wet out the area, then use thickened epoxy (consistency of peanut butter) to fill in all the damaged areas. What is the best filler to use (west system brand is what I have acess to)?

3. Sand area to re-shape damaged sections back to normal.

4. Lay 7 oz cloth over damaged area with 3 coats of epoxy over the cloth. The last coat of epoxy I was going to add west system 410 filler to help the ease of sanding.

5. Re gelcoat damaged areas. Do I have to re-gelcoat it since bottom paint is going over top of it? I figured if i ever sold the boat and they wanted to strip off the bottom paint it might look funny if this was no re-gelcoated.

Thanks again for the help on the project.

 

I wanted to add one more question. What type of resin should I use (epoxy or poly)? I believe the boat is polyester but all I have ever used is epoxy.

 

Use epoxy since that's what you are accustomed to.
One layer of cloth is not enough. I did the same damage to my sailboat last Summer and I layered and tapered about nine layers of 4" 9oz cloth tape.
I first cut about 3/4" wide out of the center and replace the wood, first sealing the wood completely. Then I copper-nailed the wood strip in place, ground smooth, and layed in those nine layers of tape, staggering each layer.
You need that kind of strength across the skeg (it appears the factory didn't know this). Build up 1/4" with cloth and you'll have a good margin of scuff-resistance and strength.