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post #17 of Old 04-09-2010
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Using a photo tach is a good idea since my tach was out of calibration with actual readings lower than what I was reading. I have a Perkins 4-108 which was new in 1985 and I've been basically running with a too low WOT for the past 25 years so I'm not really sure how dire the consequences for over proping is on engine life. I do agree that approx 80% of WOT setting is a good number for cruising and saving on fuel. I also noticed that WOT varies with current. Tied at the slip my WOT setting is around 200 rpm lower than when I'm in open water. One thing I want to see is how this setting changes with current. My theory is that going against a current, my WOT rpm will be higher. How much is the real question. I do have a max prop and have varied the pitch to see how performance changes. FWIW WOT rpm is 2300 rpm and I cruise at 2000 rpm making 6 plus knots with a 37 ft Tayana.
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