You need to grind off the exterior fiberglass until you get down to good clean fiberglass... It looks like you are going to need to get rid of almost all the fiberglass on the outside, but it appears there is still some good glass left on the inside.
Its hard to tell from the pictures on how big the area is, but you will want to grind out beyond the damage by at least 4 or 5 inches and taper the ground area as you move away from the damage.
To build back, you can use either polyester or eeeeeepoxy. Google the pros and cons of both and decide what you want to use. Assuming you use poly resin, build up the repair by applying layers of 1708, starting with the smallest piece in the middle and gradually larger as you build it up... Your probably looking at at least 5 layers to get back to a good thick keel.
Top off the 1708 glass with 2 layers of CSM to help eliminate print through of the glass. Sand everything down with 40 or 60 grit to smooth things out a bit. Then you need to apply fairing compound and fill in all the low spots... Sand, refill with fairing compound, sand, repeat, etc until you are happy with the appearance of the repair... Then paint and go boating