Hello. I am in the process of restoring an 8.7 m, 1977 columbia sailboat. Attached are 3 pictures of some damage above the one port light. Two questions.
1 what would cause this to happen
2. How do I go about repairing.
Hard to say what caused this but does not look structural. Looks like a manufacturers defect, maybe to thick gel coat layer when laying up. I would say just grind it down to see how far cracks go. If just gel coat just get some patch. I had a Columbia 9.6 for 20 years and never saw this on my boat. Some tabs came loose on the interior on the front and Boat had serious pox problem.
This is what I suggest. Grind out cracks and use thickened epoxy to fill and sand to get an even surface. I had a gallon of gelcoat made from a company called spectrum after I sent them a sample. Came out very close. Making your own match is somethingI was never good at. You can try to go to Lowes to get a formula which might help to get close. Gel coat is not self leveling so you will need to build layers (5) and then sand using increasingly finer wet sand paper.