Which situation is described as cavitation risk due to placement of the propeller?

Which situation is described as cavitation risk due to placement of the propeller?

• A. The propeller sits too near the surface of the water; you must trim your boat so the stern is sitting deeper in the water
• B. Using the wrong size propeller
• C. The water is cold
• D. The hull is heavy

Answer: (A)

Cavitation from a propeller happens when the water pressure around the blades drops below the water’s vapor pressure, forming vapor bubbles that can collapse with a pounding effect on the blades and reduce thrust. When the propeller sits too near the surface, the flow is disturbed and air can get drawn into the prop wash, creating areas of very low pressure and promoting bubble formation. Keeping the stern trimmed so the propeller remains well submerged helps maintain steady, higher water pressure around the blades and reduces this cavitation risk. The other options describe factors that affect performance or conditions not tied to the propeller’s placement. A wrong-sized propeller changes loading and efficiency but isn’t a direct placement issue, water temperature affects vapor pressure but isn’t about where the propeller sits, and a heavy hull doesn’t create cavitation from placement.

Cavitation from a propeller happens when the water pressure around the blades drops below the water’s vapor pressure, forming vapor bubbles that can collapse with a pounding effect on the blades and reduce thrust. When the propeller sits too near the surface, the flow is disturbed and air can get drawn into the prop wash, creating areas of very low pressure and promoting bubble formation. Keeping the stern trimmed so the propeller remains well submerged helps maintain steady, higher water pressure around the blades and reduces this cavitation risk.

The other options describe factors that affect performance or conditions not tied to the propeller’s placement. A wrong-sized propeller changes loading and efficiency but isn’t a direct placement issue, water temperature affects vapor pressure but isn’t about where the propeller sits, and a heavy hull doesn’t create cavitation from placement.