Do some searching on here and you fill find a lot of info. In general there are two schools of thought. One school of thought is drill out the ends to prevent propagation and on the inside of the boat apply bituthene, which is a tough sticky, waterproof roofing material (again do a search).
The other school of thought is to weld the crack. If you have cross link plastic, this method won't work. It seems there are some sophisticated methods of doing this that some pro shops use that involve applying some wire mesh and reinforcing areas around the crack.
There's the brute force approach which apparently has worked well for a lot of people which involves taking a big chunk of plastic from the same type of boat and using a heat gun to evenly head the new plastic and the hull and laying a nice rectangle around the crack and smoothing it out.
I've been welding using a cheap plastic welder and cutting a thin rod using plastic from the same manufacturer. This technique involves melting the rod and the hull and twisting the rod in to fill the crack and then smoothing it out. I apply another weld on the inside of the boat. This repair has been holding up surprisingly well for me so far. A 2" crack is pretty small, so I think you should have reasonable success with the repair.