Originally Posted by CalebD
Another reason most boat builders use a vinyl based resin (besides being cheaper) when building boats in a mold is that the Gel-coat which is sprayed into the female mold first is also a polyester based resin and bonds well with the vinyl based resin used to make the structural hull.
Just a clarification. Most builders, perhaps in excess or 95% or more of them, have historically used polyester resin for laying up hulls not vinylester. Only a select few builders lay up with vinylester. Polyester is the resin of choice for most builders, still is.
Builders like Catalina for example use only a sprayed in layer of vinylester on top of the ISO/NPG gelcoat then the boat is layed up in polyester resin. The vinylester behind the gelcoat slows or prevents osmosis from getting into the polyester resinated substrate..
For the repair the OP is doing polyester resin is more than adequate...