Question 54 ONC05 - Master or Mate of LT 200 GRT

The Correct Answer is C ### Explanation for Option C (It appears less than actually exists) When the wind and the current are moving in the same direction, the effective speed of the wind relative to the water surface is reduced. 1. **Relative Motion:** The speed at which wind generates waves, ripples, and whitecaps (the visual indicators of wind strength used to estimate speed) is dependent on the velocity difference between the air and the water. 2. **Calculation:** If the True Wind Speed (TWS) is $W$ and the Current Speed (CS) is $C$, the effective speed relative to the water surface is $W - C$. 3. **Reduced Appearance:** Since the effective relative speed is less than the True Wind Speed ($W - C < W$), the wind cannot generate the size of waves or the number of whitecaps that would normally correspond to the True Wind Speed. 4. **Conclusion:** An observer estimating the wind speed solely by looking at the sea surface (e.g., using the Beaufort scale) will interpret the smaller, less developed waves as indicating a wind speed that is lower than the True Wind Speed actually blowing. --- ### Why Other Options Are Incorrect **A) It appears at the correct speed** This is incorrect because the movement of the water (current) changes the effective force exerted by the wind on the water surface. Only if the current speed were negligible or zero would the sea surface appearance correctly represent the True Wind Speed. **B) It appears higher than actually exists** This would be the case only if the current were running *against* the wind (an opposing current). When the current opposes the wind, the relative speed of the wind over the water is additive ($W + C$), leading to very steep, short waves and a sea surface appearance that suggests a much higher wind speed than is actually present. In this scenario (wind and current in the same direction), the relative speed is reduced, making the appearance lower. **D) The appearance of the sea surface does not change** This is incorrect. The generation of waves is entirely dependent on the speed differential between the air and the water. Any significant movement of the water surface (a current) will change the wind's effectiveness in generating waves, thus changing the sea surface appearance.