The speed necessary to reach port at a designated time is 18.7 knots. The propeller pitch is 24'03", and you estimate 3% positive slip. How many RPM's will the shaft have to turn?

Correct Answer: Option A — 81 RPM

Propeller slip calculations require converting speed in knots to feet per minute, factoring propeller pitch in feet, and adjusting for 3% positive slip using the standard marine engineering formula: RPM = (Speed x 6080) / [Pitch x (1 - Slip) x 60].