Join Date: Jan 2003
Location: Maine Coast
Thanked 270 Times in 207 Posts
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My own rules for my own engine, a Westerbeke, is that the prop allow the engine to turn max rated RPM as Westerbeke strongly suggests. I then take her to hull and back off the throttle just ever so slightly. This usually puts me at 75-80% of max rated RPM on my Westerbeke. Yanmar is rather un-clear on the difference between max rated and max continuous, but on the 3YM-30 it is only 100 RPM +/-. If your boat can only turn 3200 at WOT then the prop is certainluy over pitched as you should see at least 3489 (3500) and perhaps sizing for 3600 would be better? It should ideally be double checked with a digital photo tach to make sure your tachometer is correct.
Universal, Westerbeke and Beta are all fairly strict on what they want to see the prop be able to turn at WOT. Yanmar is less clear, but I would think you should be able to at least turn 3500 +/- at WOT then run at 75-85% of that number..
When I used to work with a surveyor we always tested the engine/prop combo against the engines rating during sea trials. On nearly ever boat over propped the engine was burning or using more oil and some had seen multiple exhaust elbow replacements vs. those with properly sized props. The transom soot was always a dead give away as to an improperly sized prop. We had some boats so over propped that they would do FOUR knots at idle!!! Kind of tough on docking....
I am over on the Ericson site because my friend Tim R. had invited me over there a few years ago during a thread, which I have since forgotten. Tim is no also no longer an Ericson owner, owns a Caliber 40 LRC now, but it is a great group of guys. I still participate on many forums of boats I used to own such as the C-36 and Cape Dory forums but mostly here, SBO, cruisers and a few others.
-Maine Sail / CS-36T
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Last edited by Maine Sail; 10-14-2010 at 10:23 AM.