190. 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 revolutions per minute will the shaft have to turn?

Calculate revolutions per minute by first converting speed to feet per minute, then adjusting propeller pitch for positive slip, and finally dividing the speed in feet per minute by the effective pitch in feet per revolution, resulting in 81 RPM.