If the speed necessary for reaching port at a designated time is 19.2 knots and the pitch of the propeller is 22.7 feet, how many revolutions per minute will the shaft have to turn, assuming a 4% positive slip?

Correct Answer: Option A — 89 RPM

Propeller speed is calculated using the formula: RPM = (Speed in knots * 6080) / (Pitch * 60 * (1 - Slip)). With 19.2 knots, 22.7 feet pitch, and 4% positive slip (0.96 efficiency), the calculation yields approximately 89 RPM. This standard maritime engineering formula accounts for theoretical versus actual distance traveled.