The Hunter Wheel was a device intended to improve the propulsion of steam-powered ships and evaluated in the middle 1840s.
The vertically mounted paddle wheel, at side or at the stern, was the first propulsion scheme used with steam power, but naval authorities were concerned about the vulnerability of the wheels to damage, whether in combat or peacetime use, and sought to increase the efficiency of ship designs, as the navies of the world began to switch from wooden hulls to iron ones.
The paddles were so arranged as to project from a suitable opening in the side of the ship, at right angles to the keel.
It was discovered that Union’s engines wasted too much energy uselessly driving the paddle wheels through the water-filled cofferdam inside the ship.
This article incorporates text from the public domain Dictionary of American Naval Fighting Ships.