jefflw wrote:I assume it would be better to do this type of repair in warmer weather.
In general, epoxies like to be worked above 65F. Probably similar for other resins.
jefflw wrote:I am hesitant to cut an access hole to reinforce from the inside, as that would mean the hole would be on the deck of the cockpit similar to the forward access holes. Roger gave me some good advice re stuffing a backer if necesary through any hole and building up from that.
Working "blind" like that should be possible.
jefflw wrote:Just how thick can I expect the hull to be? I dont want to grind too much and make a big hole?
From what I saw on your picture, I would expect that you will have an actual circular opening with a wide 12:1 bevel around it, once you are done grinding. So you will need backing. Whether you bother with beveling from both sides as the West System site suggests is up to you (probably overkill).
jefflw wrote: Also from an earlier response from markst95, it would be better for me to use polyester resin so that I can finish with gelcoat.
The West System people seem to think that gelcoat over their epoxies can be managed. (There's a test report on their main site. They give the name of some types of gelcoat they tested.) Read and follow their notes on surface preparation: de-grease and de-wax your repair
before grinding (and again when you are done). Clean off any amine blushes from epoxy after it cures before you do the next layer of whaterver, etc.
I've used pre-tinted gelcoat repair kits that were matched to a line of powerboats - just picked the closest color I could find. I've also used a clear gelcoat repair material, for spots where the underlying gelcoat was good enough to give color. (Sorry don't remember the brands - for gelcoats make sure you cover the outside with some waxpaper, or plastic sheet to make sure the oxygen in the air doesn't prevent it from curing - some will have wax suspended in the mix to make that unnecessary, but better safe than forever tacky).
For fiberglass layup I've used SystemThree. They produce a very nice range of epoxies for marine use (SilverTip line). But I suspect that ultimately most similar products would work for your needs.
Consider the state of the remaining gelcoat on your hull. If there are many cracks, blemishes, dull spots you might go for painting the Hull entirely with a PU paint or something like that. In that case, you could just do an epoxy repair w/o adding gelcoat. (But you'd want to fill cracks).
Also, if you do want to repair thin cracks, you would need to widen them into a V with some scraping tool before attempting to fill them.