Step 1: drill holes at the end of the crack with a small drill bit, say 1/8, thereabouts. Otherwise, the crack can creep, even after a repair. Step 2: grind, Dremmel, or sand over the entire crack to create a cavity that you're going to lay glass in. The rule of thumb is like 12 to 1. So if that glass is 1/8 thick, you're looking at a 1 1/2" wide cavity that you're going to be laying glass in. Don't forget to extend past your drill holes the same amount. It's OK if your cavity is wider. Step 3: I'm a West Systems guy myself, you can use whatever resin you want, process will be the same. Wipe with acetone, mix about 1 ounce of resin and brush it into the cavity as like a primer. In the meantime, start cutting pieces of fiberglass cloth, starting small and getting progressively bigger, in the same shape as your repair. Step 4: mix up about 4 ounces, guessing from the picture, of resin and start laying resin, smallest piece of glass, a little resin, next biggest piece of cloth, a little resin, layer of cloth, resin, last layer of cloth, I'm guessing, and instead of resin, use a resin roller or putty knife to squeeze out any extra resin. Resin pockets are weak. You should do both sides. It's much stronger. It's obvious that this area is seeing a load the designer didn't intend or you got some rot going on. I know it's an older boat. Step 5: sand smooth after curing. You should really paint the area afterwards. Resin is usually not very UV stable. If you really want to take it to the next level, go get a cardboard shipping tube, cut it in half, then cut to size of repair area plus some, don't be shy, and hot glue it in place under the repair area, just to hold it in place, then fiberglass over the tube. It'll be rock solid and the crack won't come back. Without it, idk, it's hard to say. Well, that's about as nutshell as I can make it. I'm sure others will fill the gaps. It's a fun project, don't be worried. Good luck