West System Book and Web Page
The West people have a great webpage and book with lots of information to help you.
One thing that hasn't been mentioned is that the hull needs to be very dry to get the best repair. If the glass is soggy, you might need to tent the hull and place a dehumidifier to dry it out.
Also, if you can get access from the inside and out to do the repair from both sides, all the better. A grinder is a great tool but be very careful with it. It can take off a lot of material in a very short period of time.
If the hull is 0.25 inches thick, you need make at least a 4 inch wide repair on both sides of the crack. You need to feather out the hull gradually over those 4 inches. Make sure the hull is clean and dry. Wipe it down with acetone.
Pre-Cut multiple layers of fiberglass cloth of varying widths to build up the thickness. Coat the hull with epoxy. On a bench I place the cloth on plastic wrap with the widest piece down and coat with epoxy. I use foam brushes and a plastic spreader too. Add additional layers and reapply epoxy. Then apply the multiple layers to the hull that has been wetted out with the epoxy. Use a plastic spreader or squegee to get rid of the air. After it has totally set, wash with soap and water with a scotch brite pad to get rid of the amine blush. Then you can make fairing compound with epoxy and microballoons. Make it like peanut butter and apply to the repair area. After it is hard, you can sand it fair.
I would do the same repair from the inside, but would not remove much of the hull, just sanding it to get a good surface.
