To avoid cavitation when the propeller sits near the surface, what action should be taken?

To avoid cavitation when the propeller sits near the surface, what action should be taken?

• A. Trim the boat so the stern is deeper in the water
• B. Raise the stern
• C. Increase engine RPM
• D. Move ballast to the bow

Answer: (A)

Cavitation happens when the propeller operates with insufficient submergence, causing very low pressure around the blades and the formation of vapor bubbles near the surface. Keeping the propeller well submerged maintains higher surrounding water pressure, preventing those bubbles and preserving thrust. The way to achieve this is to trim the boat so the stern sits deeper in the water, ensuring the propeller stays under a larger depth of water. Raising the stern would lift the propeller closer to the surface, increasing the risk of cavitation. Increasing engine RPM can worsen cavitation by accelerating the flow and pressure drop at the blades. Moving ballast to the bow would shift weight forward and typically reduce stern immersion, also making cavitation more likely.

Cavitation happens when the propeller operates with insufficient submergence, causing very low pressure around the blades and the formation of vapor bubbles near the surface. Keeping the propeller well submerged maintains higher surrounding water pressure, preventing those bubbles and preserving thrust. The way to achieve this is to trim the boat so the stern sits deeper in the water, ensuring the propeller stays under a larger depth of water.

Raising the stern would lift the propeller closer to the surface, increasing the risk of cavitation. Increasing engine RPM can worsen cavitation by accelerating the flow and pressure drop at the blades. Moving ballast to the bow would shift weight forward and typically reduce stern immersion, also making cavitation more likely.