If the speed necessary for reaching port at a designated time is 19.6 knots and the pitch of the propeller is 24.6 feet, how many revolutions per minute will the shaft have to turn, assuming a 5% positive slip?

Correct Answer: Option B — 85 RPM

Calculate required RPM using: (Knots × 6,076.1) / (Pitch × 60 × (1 - slip)). With 19.6 knots, 24.6' pitch, and 5% positive slip: (19.6 × 6,076.1) / (24.6 × 60 × 0.95) = 119,111.56 / 1,402.2 = 84.9 RPM. Rounding to the nearest whole number yields 85 RPM.