Enginepowercurves.Pdf
Dave Gerr, CEng FRINA, Naval Architect www.gerrmarine.com Understanding Engine Performance and Engine Performance Curves, and Fuel Tankage and Range Calcuations By Dave Gerr, CEng FRINA © 2008 & 2016 Dave Gerr eep in the bilge of the boat you’re designing, building, Between them, pretty much everything you need to know D surveying, repairing, or operating is her beating heart— about this engine’s performance is spelled out. her engine. The recipient of endless tuning, cleaning, and fuss, it’s the boat’s engine that drives her from anchorage to Maximum Output Power - BHP anchorage. Engines, however, come in a wide array of sizes, The maximum output power curve is just what it says. It shapes, and flavors. Whether you’re repowering, determin- shows the maximum power that the engine can produce (in ing which propulsion-package option to install in a new boat, ideal conditions) at any given RPM. This is also called “brake trying to optimize perform- horsepower” or BHP be- ance on an existing boat, or cause in the old days it to understand why an en- was measured on a gizmo gine isn’t achieving full termed a “Prony brake”— a rated RPM, good informa- form of dynamometer. tion on engine behavior can These days other types of seem hard to come by. The dynos are used, but the key to deciphering engine result is the same. Note performance is the perform- that the brake horsepower ance curves that are in- is maximum in every re- cluded with the engine gard—tested on a bench in manufacturer’s literature.
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