Someone had tied a piece of string to a washer, then fed the string through a plastic screw off cap & pushed it into the hull. It appears they applied tension to the string, using the plastic cap to provide backing, then shoved some mixture of fibres & pliable crap into the breach. It never bonded with the fibreglass, they depended on a mushrooming effect, which proved inadequate.
I pulled the crap out, then used an angle grinder to quickly enlarge the hole to around 2".
Grind on a shallow angle. If you can leave the original material paper thin at the edges, so much the better. That will allow for 2-3 layers to be added on the outside, & still finish up just below the level of the gelcoat, making it easy to fair a final layer of gelcoat.
