The propeller on a vessel has a diameter of 20.9 feet and a pitch of 19.6 feet. What would be the apparent slip if the vessel cruised 447 miles in a 23 hour day (observed distance) at an average RPM of 108?
• Propeller pitch as theoretical advance per revolution (in feet) • How to convert RPM, pitch, and time into a theoretical distance run (in miles) • Definition and sign of apparent slip: (Theoretical – Observed) compared to Theoretical, and what a negative value means
• First compute the theoretical distance the vessel should travel in 23 hours with a 19.6 ft pitch and 108 RPM. Be careful with unit conversions from feet to miles. • Compare this theoretical distance to the observed distance of 447 miles. Decide whether the vessel actually traveled more or less than the theoretical distance. • Use that comparison to figure out whether slip should be positive or negative, then compute the percentage value.
• Verify you used 23 hours (not 24) when calculating total revolutions. • Check your conversion: 5280 feet = 1 statute mile. • Confirm the sign convention you’re using for slip and match it to the answer choices: is slip positive when the vessel travels less than theoretical, and negative when it travels more?
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