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Choosing the Right Prop
From its Oshkosh, Wisconsin, testing facility Merc offered us the use of a 1,900-pound Key West 2020 center-console rigged with a Mercury 150 FourStroke outboard, and a full complement of data acquisition gear. We tested each prop “light” (just the tech on board) and “heavy” (with 350 additional pounds in the boat), always with the 60-gallon fuel tank full.
Stainless steel, three blade, 14 1/2" x 18"
Top Speed/Light: 46.5 mph @ 5,532 rpm
Top Speed/Heavy: 44.2 mph @ 5,446 rpm
0-to-20 mph/Light: 4.1 seconds
0-to-20 mph/Heavy: 4.8 seconds
Max economy: 5.72 mpg @ 3,258 rpm/23.7 mph
The 18-inch-pitch Enertia propeller delivered the best top speed and the worst hole shot. It’s expected that more pitch will equate to higher speed, since pitch is the nominal distance the propeller moves through the water for each revolution. Ergo, for the same amount of rpm, more pitch equals more speed, which our testing confirmed.
But there’s a rub: More pitch doesn’t allow the engine to rev up as high, so the top speed potential of adding pitch may be greater than the reality. Moreover, acceleration, and the ability to hold the boat up and at a steady speed at lower rpm (handy in many situations), is reduced. Think of more pitch as a higher gear: You can use it to start a vehicle moving or while climbing a hill, but it’s less than optimal. Compare the acceleration numbers of this “faster” prop with the other two Enertias and you can see the effect yourself.
Enertia props are smaller in diameter and have more moderate rake, and less aggressive cup, than the Mirage Plus props they superseded. But they have more blade area than fast bass-boat props.