Question 27Navigation Problems70% to pass
The speed necessary to reach port at a designated time is 18.7 knots. The propeller pitch is 24'03", and you estimate 3% positive slip. How many RPM's will the shaft have to turn?
AI Explanation
The correct answer is A) 81 RPM.
To calculate the required RPM, we can use the formula: RPM = (Speed in knots x 1.6889) / (Propeller Pitch in feet).
Given:
- Speed = 18.7 knots
- Propeller Pitch = 24.05 feet (24'03" converted to feet)
- Positive slip = 3%
Accounting for the positive slip, the actual speed is 18.7 / (1 - 0.03) = 19.28 knots.
Plugging these values into the formula:
RPM = (19.28 x 1.6889) / 24.05 = 81 RPM
The other options are incorrect because they do not correctly apply the formula and account for the given propeller pitch and positive slip.
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