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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.
Aluminum, three-blade, 15" x 17"
Top Speed/Light: 41.9 mph @ 5,766 rpm
Top Speed/Heavy: 41.8 mph @ 5,820 rpm
0-to-20 mph/Light: 3.4 seconds
0-to-20 mph/Heavy: 4.3 seconds
Max economy: 6.09 mpg @ 3,250 rpm/22.0 mph
The three-blade aluminum Black Max is the best-selling propeller in the world. It’s standard-issue from boatbuilders paired with the MerCruiser Alpha sterndrive and outboards up to about 135 hp. The Black Max is a generalist, with conservative geometry, designed to deliver acceptable performance in almost any situation. Blade flex and modest cupping cause the Black Max to slip more than most stainless-steel props. In our testing, it was significantly slower than the stainless-steel props but matched the acceleration of much more expensive options. The Black Max does not produce the lift of a stainless-steel prop. When running the Black Max, I noted that spray was breaking off the hull forward of a gunwale rod holder, while it broke 18 inches abaft the same rod holder with every stainless prop we tested. I had to trim down to keep the prop from losing bite on the water even when making modest turns — and it blows out immediately when overtrimmed. Made of aluminum, it’s easy to ding up, even beyond repair, with a bottom strike.