The big ship you see there has pulleys and chains. Well, back in the old days during pirate time, Captains would keelhaul shipmates by tying them to pulleys and lowering them in the water. Thus, leading the pulleys to the other side of the ship, scraping the shipmates on the bottom of the ship. Many pirates died from lack of air and injuries back then. That is why the name is Keelhaul! Torturous don't you think!