Stern Drives / Outboard's are the majority of powerboats. Stern Drives are also called Inboard / Outboard (I / O). Unlike the Twin or Single Inboard which has a propeller set at a fixed angle and must rely on a rudder for turning, these engine types steer by pivoting the propeller to the right or left. Stern Drives and Outboards can also be tilted up or down to trim the boat. In the case of the Outboard, the entire engine pivots, while in the case of the Stern Drive or I / O, the "Inboard" engine remains in place while the "Outboard" stern drive unit, mounted on the outside of the transom, pivots. With either engine, the propeller wash is directed to the right or left and the water flow, known as directed thrust, forces the boat to turn.
With directed thrust steering, you'll always have steerage whether your're going forward, backward, fast or slow. As long as your propeller can turn, so can your boat; you needn't wait for headway or sternway before you can steer. Steering in reverse, however, is still not quite as effective as going forward.
On the other hand, boats with rudders do have a noteworthy advantage over direct thrust steering: A boat in motion can be steered by the rudder even if the engine has been cut. If you have a headway and your engine suddenly quits, you'll have a better chance of steering out of the way of trouble with a rudder than with an Stern Drive or Outboard. While a Stern Drive or Outboard does provide a small amount of steerage due to its underwater profile, it's not nearly as effective as a rudder.