What effect do slip and cavitation have on the speed of the vessel?

What effect do slip and cavitation have on the speed of the vessel?

• A. Increase speed
• B. No effect
• C. Slow speed
• D. Improve maneuverability

Answer: (C)

When a propeller isn’t converting all of its power into forward motion, the vessel slows down. This happens because the propeller’s pitch is the distance it would move through water in one revolution if the water offered no resistance. In reality, water resists and the blade creates swirling and eddies. The difference between the theoretical advance and the actual forward movement is called slip. The more slip there is, the less thrust you get for the same engine speed, so the ship’s speed drops below what the pitch would suggest. Cavitation compounds this by forming vapor bubbles on the blade when local water pressure falls below the water’s vapor pressure. Those bubbles collapse violently, causing erosion and reducing the blade’s ability to push water effectively. That means even at the same engine speed, thrust is reduced, and speed falls. So both slip and cavitation decrease speed; they don’t improve speed or improve maneuverability as a direct result.

When a propeller isn’t converting all of its power into forward motion, the vessel slows down. This happens because the propeller’s pitch is the distance it would move through water in one revolution if the water offered no resistance. In reality, water resists and the blade creates swirling and eddies. The difference between the theoretical advance and the actual forward movement is called slip. The more slip there is, the less thrust you get for the same engine speed, so the ship’s speed drops below what the pitch would suggest.

Cavitation compounds this by forming vapor bubbles on the blade when local water pressure falls below the water’s vapor pressure. Those bubbles collapse violently, causing erosion and reducing the blade’s ability to push water effectively. That means even at the same engine speed, thrust is reduced, and speed falls.

So both slip and cavitation decrease speed; they don’t improve speed or improve maneuverability as a direct result.