Q.
Does it make any difference where the outdrive is vertically
positioned on my stern drive? A.
Generally it is best to mount the outdrive on the transom so that the
cavitation plate is located approximately 1" below the bottom
of the keel or gull if there is no keel.
Stern drives on houseboats are generally located deeper
in the water and may have strut extensions.
High performance ocean racers will position the cavivitation
plate even with or above the hull bottom for best performance.
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Q.
Will a propeller change help my I/O installation?
A.
Generally the boat manufacturer exhaustively tests the various models
to insure that the boat performs properly.
If, however, the owner increases the boat displacement
by installing heavy optional equipment, a different propeller
will be required. In
almost all cases, the propeller to be used would be comparable
in diameter but have less pitch.
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Q.
Why won't my stern drive perform as well as another stern
drive of comparable length, beam, weight, and I/O installation?
A.
Differences in hull design, such as hull dead rise, position of center
of gravity and transom angles can account for significantly different
performance. Transom
angle is important since it governs the maximum tilt setting of
the stern drive and consequently the shaft angle.
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Q.
My houseboat plows when the stern drives are tilted to
the furthest lock bar position.
In an attempt to correct the bow-down attitude, the propellers
cavitate. Why? A.
The bow-down attitude results form the longitudinal position of the center
of gravity being forward of midships.
Merely changing shaft angle will not correct the severe
plowing which would be experienced.
As the lower unit is tilted toward the furthest lockbar
position, effectively changing the shaft angle, the depth propeller
is immersed is decreased and ventilation will occur causing a
breakdown of thrust. This
phenomenon is sometimes mistakenly termed cavitation
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Q.
Will a 4-blade propeller increase the performance of my
houseboat? In many instances, yes.
Many stern drives are limited by aperture design to the size
propellers that can be swung; the diameter can have better propeller
efficiency than the compromise 3-blade under such operating conditions.
A 4-blade propeller will provide better acceleration, better
cruising performance, better maneuverability, and result in a smoother
ride. |
Outboard 
