Welding is the only appropriate fix for aluminum. Anything else just makes a good repair harder.The crack needs to be ground out and tig welded and filled. If you have a floor in your boat and it is removable, you might want to pull it and check all of the horizontal ribs for cracked welds. if you hit something hard enough to break one, it's very possible there are more.
2015 Seaark 1872 MV CC Etec-90
Helix 12 CHIRP SI, HB 1199, MinnKota Riptide ST80/i-pilot Link, Bob's Hydraulic
Bitter Gun Owner