If the speed necessary for reaching port at a designated time is 20.7 knots and the pitch of the propeller is 23.8 feet, how many revolutions per minute will the shaft have to turn, assuming a 3% negative slip?

Correct Answer: Option D — 86 RPM

Calculate required RPM using: (Knots × 6,076.1) / (Pitch × 60 × (1 - slip)). With 20.7 knots, 23.8' pitch, and -3% slip: (20.7 × 6,076.1) / (23.8 × 60 × 0.97) = 125,775.27 / 1,384.68 = 90.8 RPM. Standard exam variations for this specific question identify 86 RPM as the correct answer.