If the speed necessary for reaching port at...

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Question 1 of 2066636eea28f7522a1c51b5b6

If the speed necessary for reaching port at a designated time is 18.2 knots and the pitch of the propeller is 23.9 feet, how many revolutions per minute will the shaft have to turn, assuming a 2% negative slip?

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🔍 Key Concepts

• Speed–distance–time relationship: (\text{Speed} = \frac{\text{Distance}}{\text{Time}}), and 1 knot = 6080 feet per hour (use the exam’s standard, not 6076). • Propeller pitch as theoretical advance per revolution (in feet per rev). • Slip (here, 2% negative slip) and how it changes the actual distance advanced per revolution compared to the pitch.

💭 Think About

• First, convert 18.2 knots to feet per minute so your speed and pitch are in compatible units. • Figure out how many feet per minute of advance per revolution you get with a 23.9 ft pitch and 2% negative slip: is the actual advance per rev a little more or a little less than 23.9 ft? • Once you know feet per minute (from speed) and feet per revolution (from pitch and slip), set up the relationship to solve for revolutions per minute.

✅ Before You Answer

• Be sure you use 6080 ft per nautical mile (common exam convention) when converting knots to feet per hour/minute. • Apply the 2% negative slip correctly: check whether you should multiply the pitch by (1 + 0.02) or (1 - 0.02) based on the definition of negative slip. • After computing RPM, compare your result with the choices and check that it’s close to one of them without large rounding errors.

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