If the speed necessary for reaching port at a designated time is 20.7 knots and the pitch of the propeller is 23.8 feet, how many revolutions per minute will the shaft have to turn, assuming a 3% negative slip?
• Relationship between speed, pitch, and RPM for a propeller (distance per revolution) • How to convert knots to feet per minute • Meaning of 3% negative slip and how it changes the effective advance per revolution
• First, convert 20.7 knots into feet per minute so you know how many feet the vessel must travel each minute. • Use the idea: (pitch in feet per revolution) × (RPM) = theoretical feet per minute, then adjust this for 3% negative slip. • Ask yourself: with negative slip, does the actual distance advanced per revolution become slightly more or slightly less than the pitch, and how does that affect the required RPM?
• Be sure you use 1 nautical mile = 6076 feet (unless your exam specifies 6080) and 1 knot = 1 nautical mile per hour. • Confirm you change hours to minutes before solving for RPM. • Double‑check whether you should multiply or divide by 1 − 0.03 (or 1 + 0.03) when incorporating a 3% negative slip.
No comments yet
Be the first to share your thoughts!