Killer whale
There is a population which lives near Spain and Portugal and which has specialized on attacking sailboats. They do not attack powerboats. This behaviour is mystery, as the whales cannot use glassfibre as a food. Most likely the whales practice attacking large sharks and whales, as the underside of a sailing boat resembles a large whale or a shark. They have damaged several boats, but so far none has sunk and no humans have died on their attacks.