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PROPELLER INFORMATION
PROPELLER SELECTION
The Top Speed 2 has been tested with many engine/propeller
combinations. A balanced Octura Models X440 has worked
well with both stock and modified engines. Octura Models
X-Series provides an extensive selection of propellers. In the
Octura prop series, the last two numbers indicate the diameter
in millimeters. For example, the X442 is larger than the X440
in diameter by 2mm while the X438 is smaller by 2mm. The
X500 and X600 series have more pitch than the X400 series.
The Prather 215 propeller is another possible choice.
Pitch and diameter of propellers is similar to gear ratios in cars.
For instance, an Octura X640 might provide more top end
speed than the X440, but not accelerate out of a corner as
quickly. Once a base line of performance has been established
with a propeller like the X440, changing propellers will provide
an opportunity to compare performance.
BALANCING A MODEL BOAT PROPELLER
To avoid damaging the lower unit propeller shaft assembly,
balancing metal propellers is highly recommended.
Balancing a propeller requires the use of a balancing device
such as the Top Flite
Power Point
®
metal files, and 400-grit wet/dry sandpaper. The front,
rounded side of the propeller, is the surface from which
material is removed. Follow the curvature of the propeller
surface. Continue checking the propeller on the balancer
until the propeller is balanced. 400-grit wet/dry sandpaper
will provide a smooth finish.
Note: While polishing a propeller improves its appearance,
it does not improve performance.
balancer (TOPQ5700),
®
PROPELLER THRUST ANGLE
As an initial starting point, you will want a neutral prop thrust
angle and the propeller depth set with the centerline (c/l) of
the propeller shaft 1/8" [3mm] above the bottom riding
surface of the sponsons (See Figure 3 above). The propeller
depth/thrust angle can be established by placing the Top
Speed 2 with engine attached on the "Setup Board" side of
the Starting/Setup Stand. Loosen the cap head screws
holding the engine to the transom and the thrust angle
adjustment screws on the motor mount to adjust the engine
height/prop thrust.
Retighten all the screws upon establishing the recommended
prop depth/thrust angle.
Propeller depth and thrust angle will vary with propellers of
different pitch and diameter. Determining optimum propeller
depth and thrust angle settings is accomplished by
observing the boat while running at full throttle.
Neutral Propeller Thrust – Provides thrust without letting the
thrust affect the ride attitude (bow upward/bow down) of the hull.
Positive Propeller Thrust – Causes a "bow upward" ride
attitude. A "bow upward" ride attitude increases the chances
of the hull "blowing over" (flipping backwards) along with
decreasing the cornering ability.
Negative Propeller Thrust – Causes the hull to ride "stuck
down" (flat on the water). A "stuck down" ride reduces the
speed and can cause the boat to submerge in a turn.
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