527. If the speed necessary for reaching port at a designated time is 18.2 knots and the pitch of the propeller is 23.9 feet, how many revolutions per minute will the shaft have to turn, assuming a 2% negative slip?

The shaft must turn at 76 RPM. This is calculated by converting the ship's speed to feet per minute, accounting for the 2% negative slip to determine the propeller's effective advance, and then dividing the ship's speed by the effective advance.