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Old 06-06-2008, 04:14   #16
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Originally Posted by CSY Man View Post
As for the Max continous RPM, you say 85%.
Is still a special recommedation for Yanmar due to their designs, or is it general for most diesels?

I have heard 70% of max contious as the target, and have been running my Perkins 4-108 at that speed:
Max RPM 4000, max contious 3000, so I have been running at 2100 RPM and the engine seems to like it..No smoke, fuel consumtion 0.55 gallons per hour, minimal oil consumption and no vibration.

85% would be 2550 RPM, and it seems kind of "busy" at that speed.
Will take a moment to get to the 85% bit but bear with me .

Engine manufacturers describe their various ratings for their engines based on the service they are targeted to - so, for instance, the same engine may be governed to more revs so more fuel and power in an intermittent type duty such as a ferry with many stop starts, or for a patrol craft which may only require to run at full and high power sometimes and then only for short periods but run at slow cruise (compared to max speed) with low power for the rest of the time, than it would be for more onerous service. The less onerous the service the higher the rating for basically the same engine.

The highest rating is normally for engines targeted at pleasure boats and that will include a statement along the lines of must not be run at more than X rpm for more than Y hours in any 24 hours - Y is often around 2 hours. The lowest rating is for vessels that run continuously or are subject to heavy drive requirements such as tugs - normally referred to as continuous rating but one has to be careful in that some engine manufacturers (MTU and Cat for example) call the maximum rated revs of their non-continuous rated engines as being their Maximum Continuous Rating (or MCR) so can lead to confusion.

Across all these ratings the figure of operating at 85% maximum revs is a generally accepted rule for balancing engine service life and cruising the vessel at its required design cruise speed - so a design brief for a new vessel may state something along the lines of operational speed to be X knots at 85% (say) of the engines maximum rated revs for the particular service.

But one has to keep in mind that running a pleasure rated engine at 85% max revs may be the same as running a lower rated but otherwise pretty much the exact same engine (but governed to slower revs, less fuel and less power) at full revs. Small sailboat engines are basically all pleasure rated and have no alternative lesser commercial service type rating but one should keep the aforegoing in mind and so it is not a good thing, in my view, to run a pleasure rated engine at anything close to its maximum revs.

Similarly, in my view, it is not a bad thing to run a pleasure rated engine at cruise at revs less than 85% max as those could be the revs the engine would normally be run at if it had a more conservative rating for a commercial type service. In fact I suspect if you run it at somewhat less than 85% a longer and more reliable life will accrue but I have no evidence of that and furthermore most engines in pleasure boats die of old age or lack of care rather than use. But I do know that pleasure rated engines in commercial vessels (sometimes done for lower initial engine capital cost reasons or for more power from lighter weight engine, or simply because the boat is actually a production boat whose builder meant it for the pleasure market not the commercial one) which are run for long periods every day, even at cruise, don't last.

In our own case we find we cruise at around 72-75% of max revs, that getting us to the point where many more revs (and hence fuel) is required to make significant increases in boat speed. It also causes the steering to rattle if we use higher revs (the turbulence from the prop on a semi balanced spade rudder feeds back through the light steering) .

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Old 06-06-2008, 17:45   #17
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I have always heard 75/75. That is 75% power 75% of the time with a good alternative to run at 75% power for the first 1/2 hour of the day to warm up the oil and then 75% for 1/2 hour about 1/2 hour before shutting down. In between it can be run at lower power settings without problems. Apparently it's low oil temp. that will cause most of the problems and running it at low power settings will not heat up the oil to proper operating temps.

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Old 29-07-2012, 04:29   #18
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Re: Yanmar Tips

Before I order new cylinder liners does anyone happen to have four of them suitable for a 4107 ?

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Old 29-07-2012, 05:04   #19
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Re: Yanmar Tips

Overheating?I,have a Yanmar 4JH3E,While running at 2900 RPM'S I,have No problems.I,Ran aground while backing and such to get off I,watched my temp go up almost to Max,as soon as I,got off it returned to normal operating temp,I,never had such a hard grounding before,is what happened normal?
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Old 06-01-2018, 04:35   #20
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Re: Yanmar Tips

Originally Posted by GordMay View Post
Caveat emptor: E. & O. E. - While every endeavour is made to ensure the information in this posting is correct, please email me if you find any mistakes so that they can be corrected.



The propeller controls the maximum rpm under load. On Sailboats, there is no substitute for propeller diameter. Fit the largest diameter prop that will fit in the space (aperture) available*. You need to take into account the available gearbox ratios.
e.g. a 3GM30 with a 2.36:1 ratio gearbox will swing a 15 inch (380mm), a 2.61:1 ratio will swing a 16 inch (405mm) and a 3.2:1 ratio will swing an 18 inch (460mm) diameter propeller.

*Prop’ Clearances Rules of Thumb:
- The clearance between the tip of the prop and the hull = about 15% of Propeller Diameter
- The clearance between the rudder and the nearest point of the propeller = about 15% of Prop’ Diameter

- The clearance between a full keel and the leading edge of the propeller, measured half way out along the blade from the center of the shaft = about 30% of Prop’ Diameter, at half the radius from shaft centreline.
- The clearance between the prop strut bearing and the propeller hub = about equal to or 1.5 times Shaft Diameter.

Fit as large a diameter propeller as possible, taking into account the available gearbox ratios.
e.g. a 3GM30 with a 2.36:1 ratio gearbox will swing a 15 inch (380mm), a 2.61:1 ratio will swing a 16 inch (405mm) and a 3.2:1 ratio will swing an 18 inch (460mm) diameter propeller.

Propeller pitch is determined by boat speed and is calculated for individual boats.

Engine Gearbox Propeller diameter Recommended
model model ratio Inches millimeters Max. Displacement

1GM10 KM2P 2.21 12 295 < 5,000#
2.62 13 325
3.22 15 370

2GM20 KM2P 2.21 13 340 < 10,000#
2.62 15 375
3.22 17 425

3GM30 KM3P 2.36 15 380 < 15,000#
2.61 16 405
3.20 18 460

* Rotation: All Yanmar Engines are 'Righthand' (RH) Clockwise rotation, EXCEPT for Saildrives, which are 'Lefthand' (LH) or anti-clockwise.


Caveat emptor: E. & O. E. - While every endeavour is made to ensure the information in this posting is correct, please email me if you find any mistakes so that they can be corrected.

Best regards, and happy motoring (when you can’t be sailing),
Old thread I know but hawk eyes here just picked a minor error and with Gord's blessing, I am offering the correction.

There is a minor error in the propeller section regarding rotation. The statement that all Yanmar engines (except sail drives) use RH props. While true for the engines have listed, it is not true for Yanmar YSx series. These all have LH props.

I understand ( but don't know for sure) that the S series also have CCW rotation (i.e. LH props).

Note: my emphasis in the quoted section
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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Old 06-01-2018, 21:43   #21
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Re: Yanmar Tips

If your Yanmar doesn't reach its rated maximum rpm and its maximum rpm goes lower over time, check the mixing elbow for a black diamond hard deposit. If you get this deposit often like this, check that you're not overpropped (that is, too big prop or too much pitch, too much prop for the engine).

Overpropping is like a truck lugging up a long hill.

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