Sterndrive

The outdrive can be matched with a variety of engines in the appropriate power range; upper and lower units can often be purchased separately to customize gear ratios and propeller RPM, and lower units are also available with counter-rotating gearing to provide balanced torque in dual-drive installations.

Other brands of sterndrive include MerCruiser (produced by Brunswick Corporation's Mercury Marine, which also manufactures outboard motors).

The history of stern drive power begins in the First World War with the production of the MAS of Isotta Fraschini, with two counter-rotating propellers.

During the 1950s, he and fellow engineer Jim Wynne worked at Mercury under founder Carl Kiekhaefer, who was initially dismissive of and opposed to a technology that would later capture 80% of the market.

Advantages of the sterndrive system versus inboards include simpler engineering for boatbuilders, eliminating the need for them to design propshaft and rudder systems; ease of trailering and shallow water maneuvering (with the drive trimmed up); also, a significant space savings with the engine mounted all the way aft, freeing up the boat's interior volume for occupancy space.

With both inboards and stern drives there is a fire and explosion hazard from gasoline fuel vapors within the engine compartment.

Typically these boats must run a blower for several minutes prior to starting the engine, and when idling or moving below cruise speed.