A propeller repair shop can increase or decrease cup to alter engine rpm to meet specific operating requirements on most propellers.
Cupping will usually reduce full-throttle engine speed about 100 to 200 RPM below the same pitch propeller with no cup. Cupping benefits are so desirable that nearly all modern recreational, high-performance or racing propellers contain some degree of cup. Cupped props will usually allow a faster top speed and more midrange efficiency by allowing more positive trim with less prop slip. When the trailing edge of the blade is formed or cast with an edge curl it is said to have a cup. Theoretically, this propeller would move forward 21″ in one revolution. When a propeller is identified as 13 3/4 x 21, it has a 13 3/4″ (35 cm) diameter with 21″ (53 cm) of pitch. Pitch is the distance that a propeller would move in one revolution if it were moving through a soft solid, like a screw in wood. Choose the propeller with the larger diameter that allows the engine to operate in the upper rpm range.ĭiameter is the distance across the circle made by the blade tips as the propeller rotates. Mid-range performance is a compromise of the above two applications. Mercury offers many excellent performance propellers including LAZER II, MIRAGE PLUS, and the BRAVO ONE Performance Series. The propeller uses power to transfer a higher propeller pitch (inches traveled per revolution), and more rake (bow lift) into more speed with a result of lowering engine rpm at wide-open throttle operation. Within the range, however, horsepower is usually increased with rpm. Most engines develop maximum horsepower within the recommended wide open throttle range. The best hole shot is generally achieved with a propeller that allows an engine to gain rpm as rapidly as possible without detrimental ventilation or slippage. BLACK MAX, ALPHA and HIGH FIVE are excellent propeller families that would fit this application.
Depending on the specific boat/engine combination, some propellers will perform better than others at attaining all three objectives. Correct propping for your boat is going to involve a compromise between hole shot, midrange and top end performance. What propeller will get the best performance for hole shot, midrange and top end?
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