The propeller on your vessel has a pitch of 22.8 feet. From 0800, 18 April, to 1020, 19 April, you steamed an observed distance of 403.6 miles. If your average RPM was 74, what was the slip?
• How to compute theoretical distance from propeller pitch, RPM, and time • Formula for propeller slip % using theoretical vs observed distance • Converting hours and minutes into decimal hours correctly
• First, how long (in hours) is the time interval from 0800, 18 April to 1020, 19 April? Convert it to decimal hours. • Given RPM, pitch (in feet), and total time, how do you find the theoretical distance the vessel would travel with 0% slip? Make sure units all match (feet vs nautical miles). • Once you have both theoretical and observed distances, which slip formula uses (theoretical − observed) and which uses (observed − theoretical), and how does that affect the sign (+ or −) of slip?
• Confirm your time interval in hours is correct before doing any other calculation. • Be sure to convert feet to nautical miles accurately (use 6076 feet per nautical mile). • Double-check the sign of slip: is the vessel traveling less than, or more than, the theoretical distance? This determines whether slip is positive or negative.
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