If the speed necessary for reaching port at a designated time is 15.7 knots and the pitch of the propeller is 23.4 feet, how many revolutions per minute will the shaft have to turn, assuming a 6% negative slip?

Correct Answer: Option C — 64 RPM

Negative slip occurs when the vessel speed exceeds the theoretical propeller speed. Using the formula RPM = (Speed * 6080) / (Pitch * 60 * (1 - Slip)), where slip is -0.06, the denominator becomes 1.06. Calculating (15.7 * 6080) / (23.4 * 60 * 1.06) results in approximately 64 RPM.