Actually boats here in OZ are made from polyester, vinylester and epoxy.
Vinylester use to be the most popular as it was a hybrid poly with some epoxy chains thrown in for strength and osmosis protection and was cheaper than pure epoxy.
Most of our boat industry has moved to China or SEA now because of cheap labour and less strict EPA regs. Who knows what they are made of now
Also Gelcoats, flowcoats etc.. define a layer not a resin type, Gelcoats are special resins that are designed to form the first surface of a composite mould or part they're specially formulated to provide the part or mould surface with properties such as resistance to UV degradation and osmosis. They can be made from any resin base, so if you have Poly you use a Poly based Gelcoat if you have Epoxy you use a Epoxy based Gelcoat.
I was always taught
Poly only sticks to Poly
Vinyl sticks to all
Epoxy sticks to all
But who knows as the formulas from different companies change and I have had different brands of Poly which have not stuck well to each other. Was it weather, bad catalyst, bad prep who knows.