The propeller on a vessel has a diameter of 20.6 feet and a pitch of 23.4 feet. What would be the apparent slip if the vessel cruised 538 miles in a 24 hour day (observed distance) at an average RPM of 87?

Correct Answer: Option C — -11.6%

Apparent slip is calculated as (Engine Distance - Observed Distance) / Engine Distance. Engine distance is (Pitch * RPM * 60 * 24) / 6076.1. With a pitch of 23.4 feet and 87 RPM, the engine distance is 608.6 miles. The slip is (608.6 - 538) / 608.6, resulting in -11.6%.