The propeller on a vessel has a diameter of 25.3 feet and a pitch of 23.2 feet. What would be the apparent slip if the vessel cruised 515 miles in a 23 hour day (observed distance) at an average RPM of 93?

Correct Answer: Option A — -5.2%

Engine distance: (93 * 60 * 23 * 23.2) / 6076.1 = 489.5 miles. Slip: (489.5 - 515) / 489.5 = -0.052, or -5.2%. Negative slip indicates the vessel is being assisted by external forces, such as a strong following current, resulting in an observed distance greater than the theoretical propeller advance.