ok 2 solutions !
put the boat in a tub of water and drop colourd dye into the water like red it works good then plung the boat in as far as u can with your hands and then see were the water comes in from the dye marks !

OR
you could take out all the stuff in the hull and fill the hull up with water and set it on paper then lift it up after like 20 seconds and see where the water mak is then follow the water strean to find the crack or whole !