Question 74Navigation Problems70% to pass
The propeller on a vessel has a diameter of 21.5 feet and a pitch of 24.5 feet. What would be the apparent slip if the vessel cruised 458 miles in a 23 hour day (observed distance) at an average RPM of 78?
AI Explanation
The correct answer is A) -5.6%.
To calculate the apparent slip, we can use the formula:
Apparent Slip = (Theoretical Speed - Actual Speed) / Theoretical Speed x 100
The theoretical speed is calculated using the propeller diameter, pitch, and RPM:
Theoretical Speed = Propeller Diameter x Pitch x RPM / 33,000
Theoretical Speed = 21.5 ft x 24.5 ft x 78 RPM / 33,000 = 481.68 miles
The actual speed is the observed distance of 458 miles in 23 hours, which is 19.91 miles per hour.
Plugging these values into the formula:
Apparent Slip = (481.68 miles - 19.91 miles) / 481.68 miles x 100 = -5.6%
The other options are incorrect because:
B) -12.3% is too high
C) +12.3% is the wrong sign, as the slip is negative
D) +5.6% is the wrong sign, as the slip is negative.
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