The problem from working from the bottom with out flipping the boat is gravity. You are wanting the epoxy and glass to seep into not separate from your working surface but if you use the vacuum bag method that will overcome the gravity issues.
Things to do:
1. grind, grind, grind to there is no more crack and then feather it out 4 to 6” out from there. If you run out of hull glass and put a hole in the boat’s bottom so be it.
2. determine if you have to go into this project from the inside. If you do that means removing the CC, and gas tank, it’s deck, and removing the wood center stringer.
3. rebuild with epoxy and glass to ½” thick hull or maybe a little more that that. Using Vacuum bag method. Then repair scratches all around and re gel coat the entire bottom of the boat then if you are putting in the water bottom paint.
This looks like a keg of Beer type job to me + I hate working upside down. This job should be done on boat stands not on the trailer and to get her up in the air a high as possible so you can access the bottom easier. Sorry for the bad report but it is what it is.
FellowShip
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My motto: Just for the Grins
