Confirm your current configuration and status: Check the model, diameter, and pitch of your outboard's original propeller (usually engraved on the hub or blade root) and use this as a benchmark for comparison. Also, determine your boat's total weight (including crew, fuel, and equipment) and its primary navigation area (inland lakes, rivers, coastal areas).

Understand the impact of these parameters:

Pitch: Increasing pitch can increase top speed, but may reduce acceleration and gradeability (similar to using a higher gear in a car). Conversely, decreasing pitch generally improves acceleration but may sacrifice top speed.

Diameter: Generally, a larger diameter provides greater thrust, but requires sufficient engine power to drive it; otherwise, the engine will "hold back" and stagnate.

Number of Blades: Three-blade propellers are the most common and offer a good balance between efficiency, speed, and vibration. Four- or five-blade propellers generally offer better acceleration, handling stability, and reduced vibration, but may slightly reduce top speed and fuel economy.

Material: Aluminum alloy propellers are inexpensive and tough, absorbing some of the impact in collisions and protecting the engine shafting. However, they are less strong and prone to wear and deformation. Stainless steel propellers are strong, rigid, and more corrosion-resistant, offering better performance (especially high-speed efficiency). However, they are more expensive and may cause greater damage to the engine in a severe collision.

Goals and Trade-offs: Clarify your specific speed requirements. Are you aiming for top speed or a faster cruising speed? Also, be aware that increasing speed often requires trade-offs in acceleration, payload capacity, and fuel economy.

Trial and Verification (Very Important): Propeller selection theory is for reference only; actual sea trials are the only reliable method.

Use a handheld optical tachometer. In safe and legal waters, with the boat under typical load conditions, accelerate from a standstill to full steam, and record the highest engine speed achieved.

Compare the measured speed to the Yamaha engine's recommended maximum allowable speed range (please consult the engine manual).

If the RPM is too high (exceeding the red zone), the propeller is underloaded (the pitch may be too low), creating a risk of overspeed and requiring increased pitch.

If the RPM is too low (below the recommended range), the propeller is overloaded (the pitch may be too high) and the engine is stalling, requiring reduced pitch.

Only when the measured RPM falls within the manufacturer's recommended optimal RPM range does the propeller match well and the engine can deliver its full power.

Consider specialized models: For high-horsepower models (e.g., 350 hp and above), consider new high-performance propellers like the Sharrow MX. These are claimed to significantly improve efficiency, accelerate take-off speed, and overall performance, though they also come at a higher price.

Installation and Maintenance: When replacing the propeller, ensure the correct bushings and mounting hardware are used and that the nuts are tightened to the specified torque. Regularly inspect the propeller for slippage, deformation, cracks, or severe wear, and repair or replace it promptly. Keeping the boat's bottom clean and smooth can also reduce drag and indirectly increase speed.

⚡ Notes

Safety first: Never continuously over-rev the engine in pursuit of speed.

Comprehensive considerations: Speed isn't the only factor; fuel consumption, vibration, noise, and boat handling should also be considered.

Consult a professional: If you're unsure, consult a Yamaha dealer or experienced marine technician.