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post #14 of Old 07-25-2019
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Join Date: Jan 2007
Location: The house is in Kingsport, TN. Boats are on Watauga Lake and in New Bern, NC
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Re: Motoring RPM

Originally Posted by Jonah71 View Post
1988 PSC 34 Yanmar 3hm35F 2 blade prop 17X10 RH
I understand that this engine is designed to run at a peak continuous rpm of 3200. My throttle pegs at 2400. It seems I am leaving a lot of power unused and therefore losing potential speed motoring. Is the solution a throttle adjustment? What role does the propeller play in this? I have sailed the boat since I purchased it 4 years ago typically motoring at 2000-2200 rpm because this seemed appropriate given that flat out is 2400.

When we bought Irish Eyes in 2004 she had three propellers, all two blade, bronze, and solid. Installed on the boat was a 17x10, and in the locker were both a badly corroded 17x11 and a dirty 17x10. We have continued to use the 17x10 although with a clean hull and clean propeller the engine (Yanmar 3HM35F) can go over its maximum rpm (3400 rpm). With a few barnacles and with the alternator and the refrigeration compressor running (engine drive refrigeration), we come up to the red line with no smoke. I've thought about mounting the corroded 17x11 and giving it a try, but I've never gotten around to it.

According to the owner's manual, the standard 2 blade propeller is a 17x12. I figure that I have a slightly lowered pitch prop to allow the easy operation of the oversize 105A alternator and the refrigeration compressor. We motor on the ICW at 2400 rpm.

Make sure that the throttle on the engine itself (actually the governor) is fully open. Move it with your fingers and see. The only times we have not reached 3400 rpm flat out is with massive - like basketball size - amounts of growth on the hull and propeller.

Bill Murdoch
1988 PSC 34
Irish Eyes
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