The propeller of a vessel has a pitch of 19.0 feet. If the vessel traveled 183.5 miles (observed distance) in 24 hours at an average of 44 RPM, what was the slip?
• Propeller pitch as theoretical advance per revolution • How to find theoretical distance traveled from pitch, RPM, and time • Slip formula: compare theoretical distance vs observed distance and note the sign (+ or -)
• First, convert the observed distance in miles to feet, then find the total number of propeller revolutions in 24 hours using the average RPM. • Use pitch (ft/rev) × total revolutions (rev) to get the theoretical distance in feet, then compare it to the observed distance to determine the slip percentage. • Think about when slip is negative versus positive: in which case is the vessel moving farther than the propeller’s theoretical advance, and how does that affect the sign of the slip?
• Be sure you converted 24 hours to minutes correctly before multiplying by RPM. • Double-check the conversion from miles to feet (use 1 mile = 5280 feet). • When you compute slip %, carefully check whether you used (theoretical − observed) or (observed − theoretical) in the numerator so that the sign matches the physical situation.
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