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Check the tilt angle of your boat.
Usually the best operating tilt angle is achieved when the drive-shaft of the motor is
perpendicular to the surface of the water when the boat is at full throttle. It is
impossible to determine this angle without putting the boat into the water and running
with normal load and at rated full RPM. If the motor is tipped too close to the transom,
the boat will dig or plow in a bow down position, with consequent performance loss. In
addition, the boat will tend to swerve to the right and steer hard left. If the motor is
tipped too far away from the transom, the boat will "gallop" or
"porpoise" in a bow high position, and will swerve to the left and steer hard
right. All outboard motors are equipped with tilt adjustment for achieving optimum angle.
On stern drive boats without power trim, the outdrive angle will be preset by proper
factory installation, it may be adjusted, if necessary, by adding or subtracting shims
from under the front engine mounts, or a tilt pin on the outdrive (similar to an
outboard).
Center the motor on the transom.
If the outboard motor is not centered exactly on the transom the unbalanced thrust will
result in poor performance, hard steering, and possible gearcase damage.
Check the boat keel for interference.
A keel that is too deep or too wide will permit air bubbles to flow back to the propeller,
causing not only slippage of the propeller, but also cavitation "burn" which
will erode the propeller. To correct this condition it may be necessary to reshape the
keel, tapering it to approximately 1/4" in height at the transom. beginning the taper
about 30" forward from the transom. An improper keel will also cause slippage in
turns.
Keep bottom of boat clean
A major cause of poor boat performance is a fouled bottom - an accumulation of marine
growth, moss, and barnacles in sea water; and the accumulation of dirt, slime, lime, and
other matter in fresh water. Cleaning the boat bottom will greatly improve boat
performance. Anti-fouling paint will slow down the accumulation of these materials and
organisms, but in salt water it may increase erosion of the gear case due to galvanic
action. Different bottom paints also provide different performance differences. Some of
the new Teflon paints for planing hulls can actually improve the performance of a
particular hull. Some concern should be noted as to the application a well. Basically, the
smoother the better.
Also note that some hull configurations have come to the market that are deigned almost
exclusively for speed. These hulls usually have the tendency to be pigs, out of the hole.
Most of these rigs are designed to be run exclusively with the new style stainless high
performance propellers and won't even come on plain, without one.
And as the final note, it is important to spend the time and effort to get the prop
correct for how you use the boat. Sometimes that may mean more than one prop for that boat
and motor combination, depending on how, where, and when you use the boat. A lot of good
propeller shops can help you tweak the prop to odd sizes to help accomplish that goal.
Also see " PropHole" info sheet.
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