Propeller Selection
Propping the engine at the higher end of the RPM range may increase
acceleration, but decrease top boat speed. Conversely, propping the engine at
the lower end of the range may increase top boat speed but hinder
acceleration. Mercury Marine recommends selecting a propeller that allows the
engine to operate in the upper half of the recommended full throttle RPM range
with the boat normally loaded (refer to
General Information
‑
Specifications
).
This RPM range allows for better acceleration while maintaining maximum boat
speed.
All "L" models (20 in. driveshaft) are capable of operating at engine speeds of
up to 6000 RPM. This increased engine speed gives the operator a greater
range of pitch selection. However, propping at the uppermost limit of the RPM
range may not necessarily result in improved high speed performance. Boat
weight and hull design influence the effectiveness of this increased engine
speed and may decrease top boat speed.
If full throttle operation is below the recommended full throttle range, the
propeller must be changed to prevent loss of performance and possible engine
damage. On the other hand, operating an engine above the recommended
operating RPM range will cause higher than normal wear or damage.
Generally, there is a 200‑300 RPM change between propeller pitches.
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If changing conditions cause the RPM to drop below the recommended range
(such as warmer, more humid weather, operation at higher elevations,
increased boat load, or a dirty boat bottom/gearcase), a propeller change or
cleaning may be required to maintain performance and ensure the outboards
durability.
Check full‑throttle RPM, using an accurate tachometer, with the engine trimmed
out to a balanced‑steering condition (steering effort equal in both directions)
without causing the propeller to break loose.
GENERAL INFORMATION
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Summary of Contents for 250 XS OptiMax
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