Depending on the depth; it's probably safer going off in the water. 5' of water is going to dampen most explosions better than a boat hull. And if it's armed,

Depending on the depth; it's probably safer going off in the water. 5' of water is going to dampen most explosions better than a boat hull. And if it's armed, as you indicate, it's an even worse idea to use magnets around it.