If the speed necessary for reaching port at a designated time is 16.4 knots and the pitch of the propeller is 23.8 feet, how many revolutions per minute will the shaft have to turn, assuming a 6% positive slip?

Correct Answer: Option C — 74 RPM

Applying the standard slip formula: RPM = (Speed * 6080) / (Pitch * 60 * (1 - Slip)). With 16.4 knots, 23.8 feet pitch, and 6% positive slip (0.94), the calculation is (16.4 * 6080) / (23.8 * 60 * 0.94). This yields 74 RPM, representing the required shaft speed for the desired advance.