I guess we are getting into a semantic confusion between "a gelcoat" and "gelcoat". "A gelcoat" is applied to a mold, "gelcoat" is the stuff applied for "a gelcoat". If "gelcoat" is applied to the outside of a boat it is essentially just another kind of paint. Since the stuff is not formulated to be used like a paint you can probably find better products for the application. For example varnish or paint.

: Normally, Gel Coat cures only in the absence of air, as is the case when it's
: used in a female mold for making fiberglass boats. However, Gel coat can
: indeed be applied to the outside of a hull. To do so requires special
: activators to be added in order for the gelcoat to cure properly.
: Alternatively, a wax perparation can be sprayed over the Gel Coat to seal
: it from the air.