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post #17 of Old 01-28-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

One simplified explanation of the 24/27 hp ratings is that the HP output of an engine is directly related to the RPM. HP rises with RPM up to a max, then tails off at the very end of usable RPM range or redline (usually). At 3400, your engine is producing 24 hp, and if you push the RPM's to 3600, it is putting out 27 hp. The problem is that Yanmar does not want that engine to be run at 3600 for any long periods. Therefore, it gives it a max rating of the HP produced at 3600, but also gives the max generally usable output as 24 HP at 3400 which can be run all day. Technically it can produce 27, but you can only expect to use 24 for regular use. If you are cruising at, say, 2000 RPM,. the engine will be producing a much lower HP (perhaps 16-18) and you can look at an output graph for that engine and see just what the output is at each RPM level.

Mike sullivan
1985 Marshall 22 catboat
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