Specifications

GENERAL INFORMATION

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.) and some "XL" models (25 in.) are capable of

operating at engine speeds of up to 6300 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.