Mercury 25 EFI FourStroke User Manual page 34

Determining the Correct Pitch size ‑ First, check the full
throttle RPM under normal load condition. If the full throttle RPM
is within the recommended range, select a replacement or
upgrade propeller with the same pitch as the current propeller.
• Adding 1 inch of pitch will reduce the full throttle RPM by
150 to 200
• Subtracting 1 inch of pitch will increase full throttle RPM by
150 to 200
• Upgrading from a 3‑blade propeller to a 4‑blade propeller
will generally decrease full throttle RPM by 50 to 100
IMPORTANT: Avoid damage to the engine. Never use a
propeller which allows the engine to exceed the recommended
full throttle RPM range when under normal full throttle operation.
PROPELLER MATERIAL
Most propellers manufactured by Mercury Marine are made from
either aluminum or stainless steel. Aluminum is suitable for
general purpose use and is standard equipment on many new
boats. Stainless steel is over five times more durable than
aluminum and typically provides performance gains in
acceleration and top end speed due to design efficiencies.
Stainless steel propellers also come in a larger variety of sizes
and styles that allow you to dial in the ultimate performance for
your boat.
3 BLADE VS. 4 BLADE
Available in many sizes of both aluminum and stainless, 3 and
4‑blade propellers have unique performance characteristics. In
general, 3‑blade propellers offer good all around performance
and higher top speed than 4‑blade propellers. However, 4‑blade
propellers are usually faster to plane and more efficient at
cruising speeds, but lack the top end speed of a 3‑blade
propeller.
GENERAL INFORMATION
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