From 1020, 3 March, to 1845, 5 March, your vessel steamed an observed distance of 845.6 miles. The average RPM was 78, and the pitch of the propeller was 20'03". What was the slip?
• Slip formula and the relationship between apparent (theoretical) speed and actual (observed) speed • How to compute theoretical distance from RPM, pitch, and time underway • Sign convention for slip (positive vs negative slip)
• First, figure out exactly how many hours the vessel was steaming between 1020 on 3 March and 1845 on 5 March, then confirm your time in hours and decimals • Use RPM, pitch (in feet) and time (in minutes) to find how many feet the propeller "should" have moved ahead with zero slip, then convert that to nautical miles • Compare the theoretical distance to the observed distance to decide whether the slip is positive or negative and about how large it is as a percentage
• Be sure you convert 20'03" of pitch into feet as a decimal before multiplying by RPM and time • Remember that 1 nautical mile = 6076 feet (or 6076.1 ft, depending on the convention used in your course) when converting feet to miles • Confirm whether you are using (theoretical − observed) / theoretical or (observed − theoretical) / theoretical for the slip formula, and how that affects the sign of the answer
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