A vessel departed from point "A" at 1206 with a counter reading of 616729 and arrived at point "B" with a counter reading of 731929 at 1148 the following day. This vessel is equipped with a 20 foot 8 inch diameter propeller, with a pitch of 20 feet. The observed distance of 404.16 miles was covered at an observed speed of 16.85 knots. What should be the apparent slip for this trip?
ā¢ Propeller pitch as theoretical advance per revolution ā¢ Using the shaft counter readings to find total revolutions over the trip ā¢ Formula for apparent slip comparing theoretical distance to observed distance
ā¢ How do you convert the change in the counter reading into the total number of propeller revolutions for the trip? ā¢ If the propeller advanced exactly its pitch every revolution, what total distance would it cover, and how does that compare to the observed 404.16 miles? ā¢ When the actual distance run is greater than the theoretical distance from pitch, should the slip be positive or negative?
ā¢ Be sure you convert all distances to the same units (feet to nautical miles or vice versa) before comparing. ā¢ Use the correct apparent slip formula: (Theoretical advance ā Actual advance) / Theoretical advance (or its equivalent form). ā¢ Confirm the sign (positive or negative) of the slip based on whether the vessel actually traveled more or less than the theoretical distance.
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