This crack seems to be really deep. I did not take a close look but there's no noticeable damage on the underside. I assume this is just a gelcoat crack?
I prefer stainless steel backing plates - but wood would work. I've also used starboard as backing plates - never used wood...This is on my new to me 94 Catalina 30. The O'Day coamings are built like a tank. It was tested one stormy day and the winch mounting bolts failed with zero visible marks in the fiberglass. I gained a ton of respect for fiberglass that day
I'm leaning more towards this being a deep gelcoat crack since there's no cracks on the underside. A large wood backing plate isn't a bad idea for the future. Still seeking out a few more opinions on this crack
I'm not sure if it's cored or not. I cut into the coaming of an old C27 once and it had a LOT of core. Very well built. I think your analysis of this is very good, especially regarding backing plates and compressionIs the area solid glass or cored there? From the looks of the crack and your statement that the underside is fine my guess is there’s rotten or at least elongated holes through a core that’s allowed the top layer to shear. If there’s no core the cracks would concern me less.
If there’s underside is still fine I don’t think a backing plate will make much difference. The point of a backing plate is to spread load so the underside doesn’t collapse under compression, but if that hasn’t happened yet I’d say the original design was good enough.
I agree with others here that it's likely a thicker section of gel coat, and it can show a crack due to shrinkage as it ages. For a backing plate I would go with a quarter (or 3/8) inch of G10, set in epoxy mush. I had no such cracks but did that for all 8 of our stanchions and all 6 winches. Smaller G10 plates under the clutch stoppers also. Proactive beats "reactive" for stuff like this. (IMHO) And when these stressed-in-use parts are off the deck, over-bore, epoxy the holes, and rebore. Yup, we did that for 100% of our deck fittings.I'm leaning more towards this being a deep gelcoat crack since there's no cracks on the underside. A large wood backing plate isn't a bad idea for the future. Still seeking out a few more opinions on this crack
This is more of a general fiberglass question. This can happen to any boatYou have a specific question on a Catalina, try going to the best site for yours catalina30.com good luck