The propeller on a vessel has a diameter of 19.9 feet and a pitch of 21.6 feet. What would be the apparent slip if the vessel cruised 395 miles in a 23 hour day (observed distance) at an average RPM of 78?

Correct Answer: Option B — -3.2%

Engine distance: (78 * 60 * 23 * 21.6) / 6076.1 = 382.5 miles. Slip: (382.5 - 395) / 382.5 = -0.032, or -3.2%. Negative slip indicates the vessel is moving faster than the theoretical propeller advance, typically caused by a strong following current pushing the vessel forward.