Yes it can be repaired. I would use biaxial cloth and west system
epoxy. If you can get to the inside I would
repair it from both sides. Start by taking a grinder and grinding out the damaged area back to good fiberglass mat in the hull. Hopefully it is solid glass and no core. Also grind the inside to put some teeth into it. Once the wound is cleaned out take duct tape and cover the outside as a mold you can use plastic over the area that is open to the new glass and use the tape for strength. Then lay several layers of cloth and resin over the inside. Assuming this is under a berth or seat layup three or four layers inside and make the patch larger than the damaged area. Let this cure up for a day or two. Then take the tape off of the outside. The
repair outside will be to fair the hull back out as the inside patch will put the strength back in. Depending on how deep and thick the hull is you will likely be able to put a layer of cloth outside as well. Keep in mind you are trying to maintain hull shape so don't build it up to much. Then use the west system
epoxy with the proper filler to fair it out. You will need to build it slightly high then go back after wards and sand it to shape. Don't over apply it as it is very hard to sand. It appears the boat was bottom painted at some point in its life. After the
repair is done it was be better to bottom
paint it again as apposed to trying to polish out the old gel coat. Google West System
Epoxy and you should find plenty of info on it. I would give the hull a good wash down with bleach and water and find any other areas that need attention while you are fixing it. I agree that this
repair should be first as without a solid hull anything else is a waste.
Jay