Actually, gelcoat CAN be used with a spraygun to recoat large areas like the topsides (hull sides between gunwale and waterline), it is however a picky job and will require a gelcoat formulation that contains a wax that will "float" to the surface to seal the surface from the air in order to cure properly. Usually the surface will need to be compounded and or ultra-fine sanded then compounded after re-gelcoating. The results, if done correctly will be FABULOUS, and recreate the original finish or better.
Check out Ship-Shape -TV for an episode where this was done on a 1960 Glastron powerboat (I think DVD copies of the show are available or there maybe You-Tube videos linked to the SSTV web site.)
Having said this.... if it were me and I needed to repair a large area of the hull, I'd use one of the 2-part polyurethane or acrylic paints and get a color as close to the original as I could. Paint seems less finicky than gelcoat, even if it may not hold up as long as gel coat. Kind of funny to read an old book from 1969 that claimed that gelcoat would only last about 5 years before the gloss and color could no longer be maintained, so thye boat would need to be painted...... my DS II is 36 years old and the gelcoat looks brand new each Spring after I use a fairly light duty oxidation removing compound applied and removed by hand buffing, followed by 3-5 coats of a good marine paste wax. Look at the STUART Marine web site (current builder of the MARINER and RHODES 19) to see what can be done to restore faded gelcoat on 40+ year-old boats.... WOW!
Getting back to painting, I do not have experience with the 2-part paints, but have painted 2 fiberglass hulls with Interlux Brightside Polyurethane, and that paint held up well, gloss was still good after 5+ years. It does require careful application to be sure of not missing spots, and do not try to brush it out too much. Roll and tip may work better than just brushing. Spraying can be done, but most experts recommend the roll & tip method as less hazardous (less airborne chemicals).