I would fill in the cracks with epoxy
using a slow curing Part B that gives the epoxy
adequate time to saturate itself in to the cracks. Do a practice test on something other than your boat first. I am kind of partial to West Systems epoxy.
This will only stop the water
and probably only temporarily. There is cracking because there is flexing going on in that area. You have a problem greater than some leaking. Try to find out why there is flexing in this area. The solution will probably be building up some layers of fiberglass
with epoxy, but I am only guessing since I cannot see the problem.