Although underwater assault rifles firing drag-stabilized projectiles do exist, it is impossible to aim a shot out of the water at a target on land (or, like here, on a boat). With a choppy sea surface, you probably couldn't even see the target, but if you could, you'd need to compensate your point of aim for the light refraction at the water's surface, the strongly curved trajectory of the projectile and possibly also for disturbance of the projectile when it leaves the water.