The propeller on a vessel has a diameter of 24.0 feet and a pitch of 21.3 feet. What would be the slip if the vessel cruised 510 miles in a 24 hour day (observed distance) at an average RPM of 86?
• Propeller pitch as theoretical distance advanced in one revolution • Relationship between RPM, pitch, and theoretical distance in a given time • Formula for propeller slip percentage, including sign convention (positive vs negative slip)
• First, find how many revolutions the propeller makes in 24 hours at the given RPM. From that, calculate the theoretical distance the vessel should travel with zero slip. How does this compare to the observed 510 miles? • Decide whether the vessel is moving less or more than the theoretical distance. How does that affect whether slip is positive or negative? • Convert all distances into consistent units (feet to miles, or miles to feet) before calculating percentages. What unit conversions are needed?
• Be sure to use pitch (not diameter) to compute theoretical advance per revolution. • Use the slip % formula: (\text{Slip%} = \frac{\text{Theoretical} - \text{Observed}}{\text{Theoretical}} \times 100), and then consider the sign of the result. • Verify that your final percentage matches one of the choices including its sign (positive/negative).
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