Refers to punishment mostly associated with sailors or pirates at sea. A rope is tied to the sailor and they are thrown overboard while the ship is moving. This would sometimes result in death or serious injury, due to the sailor being dragged completely from one side, under the keel, and to the other. This style of punishment appeared first with the the Dutch, and later with the British Navy.
My friends I stand before you
To tell a truth most dire
They lust a traitor in our midst
Who haven't vote the captain's ire