A photo would help. If it really is an inch deep--it is probably in the sold glass area, which starts in front of the helm bulkhead. Again, assuming that it is in the solid glass area, and an inch deep, this is a significant damage, and needs to be rebuilt with glass. There are three choices--polyester is cheaper, and in some ways easier to work with, but does not have as good secondary bonding characteristics. The next in vinyl ester resin--better adhesion, it does allow easy application of gel coat, and is a little more expensive. The third choice is epoxy. Epoxy has the best adhesion, is stronger, but you have to choose which glass fibers (especially mat, since some of the mats have sizing which does not dissolve in epoxy, and thus not as good penetration. Gelcoat does not stick as well to epoxy. Epoxy has to be protected from Ultra violet light damage (not a major problem on the bottom of the boat).
I personally like to work in epoxy, because of the adhesion, but in your case, I would use vinyl ester resin. I would grind away all of the damaged glass; normally you want at least an 8 to one taper as you work in from damaged glass to good glass (again, a one inch deep gash leaves little of the original laminate. I that part of the boat was probably built with mat and woven roving. Today, I would be considering using 1708 which is 17oz biaxial roving at 45Degrees, stitched to 3/4 oz mat. because it is a repair, I would lay down 1.5 oz mat first, then a couple of 1708 and finally on the top, matt to build up the last amount to fair to the contour-- at least one coat of resin rolled on, and then gel coat. (You have to occlude the air from gel coat for it to set up)
It could be done in all mat, if the gouge is not as deep as indicated. In that case, I would just use polyester. There are many different ways to do this type of repair.
If the bottom of the boat is painted, then you don't have to worry about the gel coat--and just put a couple coats of finish resin, and sand it fair.
If it was a small gouge, and you were going to paint it, then MarineTex might be acceptable. Repair folks don't like MarineTex, since it all has to be ground out when you want to re-laminate a repair. The polyester does not stick as well to epoxy, as epoxy sticks (secondary bonding) to polyester. Marinetex is a good epoxy for small repairs, and some other uses, but it does not have the glass fibers in it, so there is not as much strength for a large repair.