5/30/2023 0 Comments Outboard motor dynometer curve![]() ![]() Ideally, this engine would be operating at its full 2300 rpm with the throttles at wide open and the boat fully loaded for sea. ![]() This is the power available at the output flange of the transmission where it connects to the propeller shaft, and in this case is 1,040 horsepower after accounting for gear losses of 3.7 percent. From this power, we must deduct a small percentage for friction losses in the reduction gear to get the SHP, shown by the second curve from the top (2). For this engine, the maximum rated SHP, or shaft horsepower, at the engine’s top speed of 2300 rpm is 1,080 horsepower. This is the horsepower measured at the flywheel by the engine manufacturer on a test brake, or dynamometer. The uppermost curve, (shown as number 1), is rated BHP, or brake horsepower. Along the bottom is a scale of engine speed in rpm, so we can determine the horsepower at any given rpm. To the upper left is a scale of horsepower, and it refers to the top three curves, one dotted and two solid. To understand the curves, we must first decipher the terminology used on the graph.
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