When pirates in little speedboats tried to attack Carnival's 10,000-ton Seabourn Spirit off the coast of Somalia with a grenade launcher and machine guns, they were the ones to get the surprise: The ship's crew blasted back with a sonic blaster that was developed to keep boats from attacking warships. "the non-lethal weapon sends out high-powered air vibrations that blow assailants off their feet. The equipment, about the size of a satellite dish, is rigged to the side of the ship." (link to article in Britain's Sunday Times.)
Should you put a sonic blaster on your list of site-inspection items for your next cruise meeting? I don't know, but it might not be a bad idea, depending on where you're cruising.
Update: According to CNN, the ship just outran the pirates. I like the sonic boom explanation better, but who knows which is the case.