[unclebilly]

There are only a few structural adhesives that stick to polyurethane.

3M DP8005. I recall this one having small beads in it to maintain a correct adhesion gap. I would start with this but get the crack lined up when you ‘glue’ it.

I would then cover the crack with a patch made from thin aluminum sheet riveted on with a healthy layer of DP8005 between the hull and the aluminum. You could also use windshield urethane for this part.

The key is that the glue will fix the crack and the aluminum patch will keep it from cracking again. The polyurethane will keep it all sealed up.