Whaleback

1. A type of cargo steamship of unusual design formerly used on the Great Lakes of North America, notably for carrying grain or ore. The hull continuously curved above the waterline from vertical to horizontal, and when the ship was fully loaded, only the rounded portion of her hull (the "whaleback" proper) was visible above the waterline. With sides curved in towards the ends, whalebacks had a spoon-shaped bow and a very convex upper deck.
2. A type of high-speed launch first designed for the Royal Air Force during World War II, or certain smaller rescue and research vessels most common in Europe that, like the Great Lakes vessels, have hulls that curve over to meet the deck, although the "whaleback" designation comes not from the curve along the gunwale as in the Great Lakes vessels, but from the fore-and-aft arch in the deck.
3. A sheltered portion of the forward deck on certain British fishing boats designed, in part, so that water taken over the bow is more easily shed over the sides. The feature has been incorporated into some pleasure craft – aboard which it is known as a whaleback deck – based on the hull design of older whaling boats.