Yanmar cruise RPM
- Thread starter Ken Cross
- Start date
Ken
Over 7 seasons - Olympia to San Juans/Canada Gulf Islands and return annually - 2800 rpm. I have not had any coking/carbon restrictions in the mixing elbow over these 800 plus hours.
Mine is 2GM20 direct sea water cooled. The boat is 8500# about 23 foot at the water line. We do about 6 knts and burn 6/10 gallon per hour.
Charles
Over 7 seasons - Olympia to San Juans/Canada Gulf Islands and return annually - 2800 rpm. I have not had any coking/carbon restrictions in the mixing elbow over these 800 plus hours.
Mine is 2GM20 direct sea water cooled. The boat is 8500# about 23 foot at the water line. We do about 6 knts and burn 6/10 gallon per hour.
Charles
Unless we are talking just about the 2GM20, I think it better to compare the ratio of cruising rpm's to WOT rpms. Diesels run best when they are working hard. I've always heard that running them about 75 - 80% of WOT is best. WOT on my 3YM20 is 3600 rpm. I run about 2800 - 3000 rpm. That's 78 - 83% WOT. That will push my 5 ton boat at 6 knots easily. At that rpm it burns about a gallon every 2 - 2 1/2 hours.
As I wrote this, NYSail chimed in and he is 100% correct.
As I wrote this, NYSail chimed in and he is 100% correct.
Much discussion about this over the years. Lots of opinions, but IMHO, as long as your engine reaches operating temperature at whatever RPM you choose to cruise, that should keep everything in good working order.
Our 35,000 pound boat came equipped with a 4JH2-TE engine turning a fixed three blade prop. When I'm cruising with the engine, I tend to keep it at 1,800-2,000 RPM, which pushes the boat along nicely at between six and seven knots. Whether I keep it at that RPM, or push it higher, the engine operating temperature remains the same. This has been my modus since purchasing her in 2002, with about 1,200 hours of operation with no ill effects.
Some will say that Yanmar engines like to be run hot, whatever that means. Again, as long as the engine reaches operating temperature, that should keep things cleaned out. I operate other diesel engines that seldom see 1,500 RPM over several thousand hours with no apparent ill effects.
Our 35,000 pound boat came equipped with a 4JH2-TE engine turning a fixed three blade prop. When I'm cruising with the engine, I tend to keep it at 1,800-2,000 RPM, which pushes the boat along nicely at between six and seven knots. Whether I keep it at that RPM, or push it higher, the engine operating temperature remains the same. This has been my modus since purchasing her in 2002, with about 1,200 hours of operation with no ill effects.
Some will say that Yanmar engines like to be run hot, whatever that means. Again, as long as the engine reaches operating temperature, that should keep things cleaned out. I operate other diesel engines that seldom see 1,500 RPM over several thousand hours with no apparent ill effects.
The mechanics at Mack-Boring have been very adamant in every discussion I have had with them that the marine Yanmar is a high-speed, heavily loaded diesel that benefits from high-speed operation to keep carbon build-up to a minimum. They even suggest several high-RPM throttle bumps prior to shut down to blow out any carbon.
I have a very accurate digital temp gauge on my 4JH3E and the engine runs a consistent 167 to 170 whether the engine is at 2300 RPM, or 3300 RPM, suggesting that high speed is nothing to this engine. The biggest factor in engine temp is seawater temp. Higher - Hotter.
I have a very accurate digital temp gauge on my 4JH3E and the engine runs a consistent 167 to 170 whether the engine is at 2300 RPM, or 3300 RPM, suggesting that high speed is nothing to this engine. The biggest factor in engine temp is seawater temp. Higher - Hotter.
I agree that everything I've read says diesels love to be run hard (temp will follow). But with my pitched prop I achieve hull speed at a lower rpm then others with same boat and engine. When I raise the rpm's higher I see no extra speed so I run at about 2400 rpm's (3hm35f - 1986). Engine stays at about 145 to 155 degrees. No smoke and runs smooth (after last years elbow replacement - 10 years). sister ships run at 3400.....
Guess this brings up the prop pitch. Is there an exact pitch for each engine/hull? How do you determine the pitch??
Guess this brings up the prop pitch. Is there an exact pitch for each engine/hull? How do you determine the pitch??
If a prop is under pitched it will reach the specified RPM but still be wrong. You want to be able to reach max rpm or close to it but the engine should have to work to hit those last few hundred RPM. If it just zooms up to full RPM it's underpitched.
It's not uncommon for builders to just slap a prop on there and have it be wrong. My previous boat, a Catalina 30, had a significantly under pitched 2 blade for the particular engine in that boat. I took it to a prop shop, they added pitch to it, and the performance improved substantially.
What a prop shop wants to know in order to figure out the propeller's pitch is its diameter, number of blades, the engine horse power, and the transmission gear ratio.
Also something to watch is that older (20+ years) yanmar's tend to be off. My yanmar 3GM's tach shows 2000 rpm when it is actually 2600 rpm.
Well blitz..... That's a great point. Got a new alt a few years ago.... Maybe I should get a new tach.
I typically run my 3JH3E, 39 hp, at 3,000 rpm when cruising, sometimes 3,100. It tops out at about 3,200 rpm. That is what the Yanmar service folks advised me to do. Essentially, you cannot run it too hard was the impression I got. Now has 1930 hr, 16 yr; but many hr at idle or charging at anchor.
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That's the ticket! I keep one on my boat and occasionally use it to compare to. my tach,it is within a 100 rpm, close enough for me!
Also, I think with the Yanmar tachs being off its not actually the tach instrument that's off, but the rpm sensor. Yanmar uses a sensor that I believe counts the revolutions of the fly wheel. If that is not correct, please someone set me straight.
it actually just marks the rpms as the flywheel makes a round not really counting ....this is accomplished by the break in the electric signal as the gap on the flywheel passes by the proximity switch on the bell housing
If the prop is correctly sized and pitched every Yanmar should be able to attain 100% of max rated RPM. Sadly far too many boats are under or over propped..