If the speed necessary for reaching port at a designated time is 17.4 knots and the pitch of the propeller is 25.6 feet, how many revolutions per minute will the shaft have to turn, assuming a 3% positive slip?

Correct Answer: Option D — 71 RPM

Calculate speed in feet per hour (17.4 knots * 6076.1 ft/nm = 105,724 ft/hr). Account for 3% positive slip by dividing by (1 - 0.03). Divide the resulting distance by pitch (25.6 ft) and 60 minutes to determine the required shaft speed of 71 RPM.