I would have it welded personally HOWEVER....if you wanted to test it.... I would also drill the very tip of the crack with a 1/4" drill bit. this will prevent it from growing. then I would seal the crack with silicone or 5200.... THE REASON would be to see if it does indeed flex under the forces of towing or running the boat... the sealant cracks, youve got a bigger issue than if it doesn't.