Yanmar 57 HP, max rpm 3200

Steve Dion · Dec 16, 2011

It sounds like you may be over-propped. You need to determine the MAX rated RPM for your motor (probably on the engine tag). Your engine should rev to the max rpm at wide open throttle. The normal cruising RPM is 70-80% of the max rating.

I though the turbo JH engines were rated at 3750-3800 (not sure).

Bill Roosa · Dec 17, 2011

There are 2 "max" RPMs on yanmar engines. The 1 hour rating (higher value) and the continuous rating (usually 200ish RPM less). The 1 hour rating is just that, she will run there for about an hour and then begin to have problems (usually overheat). You do not want 70-80% of the 1 hour rating, you do want 70-80% of the continuous rating.
If you have a factory prop you are fine. may need your bottom or prop cleaned though.
Yanmars have cooling systems that are not overtly hefty. In other words they operate right at the edge of the envelope. So you are going to notice changes in engine temp and oil pressure (hotter oil flows better and provides less pressure) as you call for more power. This is normal. You might notice that the water temp gauge has a place where green and red bands overlap. That pretty much tells the tale.
Some will say that diesels NEED to be run hard to keep from carboning up
Some will say that diesels NEED to be run hard occasionally to blow out the carbon
I say that just because they CAN be run hard does not mean they NEED to be.
I run my 4 cyl, 50 HP yanmar at 2300-2500 exclusively for 6 knots of speed. I've pulled the exhaust elbow after 4 years of this and it was absolutely clean, just a thin coating of carbon with no big knots or such.
So keep an eye on the gauges and as long as they are not "in the red" you should be OK
Ahhh the joys of owning your own sailboat.

Bill Roosa · Dec 17, 2011

For the record the relationship between RPM and boat speed is NOT linear. As you approach hull speed the power required to maintain that speed goes up exponentially.
So if 2500 RPM yields 5 knots and 2600 yealds 5.1 knots it is NOT true that 3000 will yield 5.5 knots (assuming your hull speed is in the 6 knot range). It is generally linear (linear part of the exponential curve) at boat speeds below 50% of hull speed though

Steve Dion · Dec 17, 2011

http://yanmarhelp.com/operate.htm

There is a wealth of information on this site.

Buck420 · Dec 17, 2011

I'm the original owner of an '01 420 w/ the same Yanmar 4JH2TBE engine (that you apparently have), and w/ the OEM 3 blade, fixed prop .

As usualy, Bill's comments are spot on.

I cruise at 22-2400 rpm. At this rpm, with a clean, newly painted bottom, you should do at least 7kt thru the water, and run all day long @ not more than 180deg F. At max rpm ( ~ 3400 for me), the boat WILL do 8kts+, but the temp does begin to rise at this"all out" rpm, and I avoid running >2400 unless I REALLY have to. In addition to gradually overheating, the fuel consumption at rpms > ~ 2500 goes up dramatically, for little additional boat speed.

I have >4000 hrs on the engine (after 11seasons) and it's still running like it was new.

Yanmar 57 HP, max rpm 3200

therobesons

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Steve Dion

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Bill Roosa

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Bill Roosa

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Steve Dion

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Buck420

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therobesons

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