Steamer is an early term for any vessel power by a steam engine rather than sails.
Early steamers were propelled by large paddlewheels. "Side-wheelers", with the paddlewheels on each side, were more seaworthy, and therefore more common in ocean waters, while "stern-wheelers", with a single large paddlewheel at the back, were more common as riverboats. Later, these were replaced by more efficient screw (or propeller) vessels.
and the fact that the boilers are always in front of the engine. Identify any one of these features on the wreck, and you can orient yourself in even the murkiest conditions.