WOW!!! after looking at the pics..that is no hairline crack..that is a serious crack/break..not sure silicon will fix that one as the structure itself is weak..I had no idea the crack was that bad...
Personally..I would stick a good gob of Shoe Goo in that area...let dry over night and be careful not to scrap that boat over a rough area..that boat would fill up with water very fast the way it is..SHOE GOO Is good for fixing larrge problems..silcon..for hair line fractures..
Walmart sells Shoe Goo for under 6.00 Warning ..try not to get Shoe Goo on your hands..left me with a rash for months