n. A vessel of which the upper deck is rounded: generally without upper works. It has a spoon-bow, with the whole of the main deck arched and meeting the side in a continuous curve. There are a number of very large hatches in the crown of the deck. The propelling machinery is in the extreme after end of the vessel. Such vessels were first used on the Great Lakes.n. In physical geography, a drift-hill of rounded profile thought to resemble the back of a whale rising above the sea.Having an arched or curved deck continuous with the side: said of a particular type of steamer. See whaleback, n., 2.n. Same as turtleback.n. A vessel of which the upper deck is rounded: generally without upper works. Such vessels were first used on the great lakes.