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Boat propulsion

The sterndrive, or stern drive, is alsoboatbuilders, eliminating the need for them
called inboard/outboard (I/O), and is a formto design propshaft and rudder systems; also,
of marine propulsion. The engine is locateda significant space savings with the engine
inboard just forward of the transom (stern)mounted all the way aft, freeing up the
and delivers power via a shaft that goesboat's interior volume for occupancy space.
through the transom to the drive unit (oftenThis is of particular significance to
referred to as the outdrive) located outsideconsumers who are interested in "pocket
the hull, which resembles the bottom half ofcruisers," boats which have amenities like a
an outboard. This unit contains the gearinghead, a galley, and separate sleeping
for the system and carries the propeller. Thequarters in a boat less than 30 feet in
boat is steered by pivoting this unit, justlength.
like with an outboard motor, and no rudder is
needed.Disadvantages of sterndrives versus straight
inboards include the fact that power must
The engine itself is usually the same aspass through two 90-degree gears to get to
those used in true inboard systems,the propeller, which is less efficient; also,
historically the most popular of which beingsince the mechanism is more complex it is
marinized versions of Chevrolet and Ford V-8more likely to experience mechanical failure
automotive engines. The most popular brand ofand require more maintenance, plus with the
sterndrive is MerCruiser, produced bymechanism located out in the water it is more
Brunswick Corporation's Mercury Marine, whichsubject  to  damage  from  submerged hazards.
also manufactures outboard motors. In 1999
the company was sued by competitor VolvoThis gearing is highly sensitive to various
Penta for monopolizing the stern driveoperating conditions. For example, it is
business.critical to not engage the drive with the
outboard drive trimmed fully upwards. Doing
Historyso could destroy components. Many boats have
separate controls for fully-upward-trimmed
The history of stern drive power begins inand a lower upward trim setting, allowing
1948, when Charlie Strang mated an aluminumboat owners to be more comfortable with
car racing engine to the lower unit of antrimming the lower unit upward. The lower
outboard motor, in order to create a marineunit has an ideal trim level where the
propulsion system more powerful than thegearing and joints align the best. This point
outboard motors available at the time. Theis easily identifiable as the drivetrain will
system would be patented ten years later by"feel" smoothest while at cruise speed at
Jim Wynne. During the 1950s, both engineersthis  trim  level.
worked at Mercury Marine under Carl
Kiekhaefer, who was initially dismissive ofMaintenance with I/Os is more complicated in
and opposed to the idea of sterndrives, butseveral ways. For example, oil changes can
would later capture 80% of the market. Inrequire complicated pumping mechanisms, and
1958, Wynne left Kiekhaefer and in less thanengine repairs are often far more complicated
90 days "invented" the stern drive. The firstthan outboards because of incredibly tight
commercial introduction of sterndrives was byspaces in the engine compartment. In some
Volvo Penta at the 1959 New York Motor Boatboats the entire engine must be removed to
Show. Kiekhaefer would introduce the firstperform otherwise trivial repairs whereas,
MerCruiser outdrive in 1961 at the Chicagowith an outboard, all one must do is pop off
Boat Show. By 1962, 16 manufacturers werethe  cover.
producing sterndrives. There was also the
Outboard Marine Company (O.M.C.); however,There is also a hazard of explosion from fuel
due to several patent wars, O.M.C. eventuallyvapors within the engine compartment.
went  under.Typically, I/O-equipped boats must run a
blower for several minutes prior to starting
Relative  Meritsthe engine, and when idling or moving below
cruise speed. The blower exchanges the air
Advantages of the sterndrive system versuswithin the engine compartment with fresh
outboards include higher available horsepoweroutside  air.
per engine and a clean transom with no
cutouts for the outboard installation and noBecause of their practical advantages and
protruding powerhead, which makes for easierattractive cost, sterndrives have become
ingress and egress for pleasure boatextremely popular especially for use in
passengers  and  for  easier  fishing.pleasure boats, and there are many models of
boats for which sterndrive power is the only
Advantages of the sterndrive system versusavailable propulsion offered.
inboards include simpler engineering for



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