IP27 Prop Pitch
At long last: Engine, prop and boat are all in balance. I'd been unable to go beyond 2700 RPM on my 18 HP Yanmar 2GM20F engine. It was like hitting a wall: no further speed, and horrible black, sooty smoke. I eliminated all likely engine causes. The elbow was new, and the engine had just been through its 1000-hour service which included, among other things, reconditioning the fuel injectors. The bottom and prop were clean. The boat was not overloaded. After researching the IPMail archives, speaking with the factory, and speaking with Michigan Wheel (the manufacturer of my prop) and one other prop shop, the consensus was to repitch the prop from 15 x 12" to 15 x 10". I did so, and the results are remarkable: full power up to 3100 RPM (and about 6.3 kts. in flat water), no smoke at all. Comfortable cruising at 2600 RPM (6.0 kts.) and 2400 RPM (5.8 kts.), all with no smoke. What a relief!
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