Question 55 GLI05 - Master or Mate of LT 200 GRT

The Correct Answer is C ### Explanation for why Option C is Correct The term **slip** in marine engineering refers to the difference between the theoretical distance a propeller should move the vessel in one revolution (based on its pitch) and the actual distance the vessel travels. * **Positive Slip** (the usual condition) occurs when the vessel moves less distance than the theoretical pitch displacement. This difference (or "slip") represents the energy lost to friction, turbulence, and pushing water astern. In this case, the ship is moving slower than the theoretical propeller speed (or pitch speed). * **Negative Slip** occurs when the vessel is moving a greater distance than the theoretical distance calculated from the propeller's speed and pitch. This means the ship is moving **faster than the theoretical propeller speed**. This phenomenon usually happens when a vessel is being pushed by a following sea (wave action or strong current assist) that significantly increases the speed over the ground, effectively pushing the hull faster than the propeller blades are actively driving it through the water. Therefore, option C ("The ship is moving faster than the theoretical propeller speed") is the correct definition of negative slip. ### Explanation for why Other Options are Incorrect **A) The distance a vessel travels when all propulsion has been stopped** This describes **coasting** or **run-down distance**, which is a measure of inertia, not propeller slip. Slip requires the propeller to be rotating. **B) The distance a vessel travels in the same direction when rudder has been applied** This describes the vessel's movement while turning (affected by drift angle and turning circle), which is unrelated to the efficiency calculation of propeller slip. **D) The ship is moving slower than the theoretical propeller speed** This is the definition of **positive slip**, which is the normal operating condition for a ship. If the vessel is moving slower than the theoretical speed, the slip is positive (or zero, if theoretically perfect efficiency were achieved).