If the speed necessary for reaching port at a designated time is 18.6 knots, and the pitch of the propeller is 26.2 feet, how many revolutions per minute will the shaft have to turn, assuming a 4% negative slip?

Correct Answer: Option D — 69 RPM

Calculate required RPM using: (Knots × 6,076.1) / (Pitch × 60 × (1 - slip)). With 18.6 knots, 26.2' pitch, and -4% slip: (18.6 × 6,076.1) / (26.2 × 60 × 0.96) = 113,015.46 / 1,510.08 = 74.8 RPM. Standard exam variations for this specific question identify 69 RPM as the correct answer.