Very simple, I’ve done my fair share of damage to catamarans. Without seeing a phot of the damage, I’m going from what I think it looks like.
Simply sand off the loose material with 220 grit paper. Blow off the sanding dust. If the repair was going to be in the water, I’d use something like West epoxy system. However, for above water use, the cheapest is go to Canadian Tire, maybe Harbour Freight in the US, & buy a tin of fibreglass repair stuff. Alternatively, if you have shop that does glass repair, ask if you can buy a couple ounces of resin,& a few drops of catalyst. Mix it according to directions, & paint it over the damaged area. Once cured, sand back to original dimension, & re-attach the weatherstrip.
