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Old 01-03-2010, 18:35   #1
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Yanmar Engines

Need some advice. On a new Jeanneau 50 DS, I have ordered the 110 hp turbo charged engine. The engine is rated at 3200 rpms. My question is how fast I should run the engine. I have been told by some mechanics that the max rpms should be 80% and by others, closer to top speed. As with my current Westerbeke, one can sense the proper max by sound, vibration, lack of black smoke, etc. Perhaps the same applies. Thanks
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Old 01-03-2010, 18:57   #2
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At 2 hp per 1000 kg you will be able to drive the hull in flat water at a good clip. Upwind and up-chop you will be using more hp. But a diesel does not like to be run light, so other than manouvering at the dock I believe you will be motoring pretty fast with this engine and hull specific. It is quite a lot of hp you have there and an easily driven hull - I have used a 110 hp in a 20.000 kg boat and it was enough and a bit to spare - upwind and in very nasty conditions.

I would try running the engine at about 2500 and see whether you 'get the feeling', just like with your Westerbeke.

b.
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Old 01-03-2010, 22:01   #3
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What brand engine? Many have a maximum and a continuous rating; their spec-sheet should reveal that.

The optimal rpm's depend on the gearbox and propeller. You should be able to reach 3200 rpm while motoring in flat water. If you can't get that high, you are overloading the engine throughout it's rpm-range. After the break-in period the boat will tell you what rpm setting she likes best and that will be different when the conditions change.

Edit: ah the title says Yanmar. My Yanmar has maximum and continuous ratings so check the spec's.

cheers,
Nick.
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Old 02-03-2010, 00:42   #4
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As Jedi says, the info will be in the engine specs, and unless its got a heavy industrial rating, which I doubt, the continuous rating is likely 70-80%. Spec's (should be online) will also give you a chart showing the hp, torque, and fuel consumption for the rpm range. I just re-powered (40hp na) and my max rpm range is 2800-3200, my max torque and best fuel economy is 1800-2200rpm, and that's where I like to run it. Proper break-in on a new engine is also very important.
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Old 02-03-2010, 01:06   #5
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if you check your yanmar user's manual i suspect you'll find that yanmar say that the engine can safely be run at low revs for long periods so long as it's run up to near full revs every so often (can't remember the details as don't have manual with me).

i have the 4LH-HTE which is turbocharged

i checked this as we were trying to conserve fuel during a recent long and rather windless passage
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Old 02-03-2010, 04:34   #6
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3200 should be reserved for use one hour out of 12. I'd consider 2900-3000 max continuous RPM.
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Old 02-03-2010, 04:51   #7
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You will probably need something like 30 Hp to drive your boat at a little under hull speed (in good conditions). Any faster and you may gain a knot or so and make a nice big wave wasting your fuel (fuel consumption has a third power relation to speed in water as a displacement boat; I seriously doubt she will plane, as soon as you try to go over the hull speed all that will happen is that it makes a nice big wave and make an extra knot). Depending on your prop you may achieve cruising speed at even less than 2500 rpm. I agree it is a good idea to burn your engine clean every now and then. It is also nice to have some reserve power for less than ideal conditions; with 110 Hp you have more than enough power. At 50 feet I guess your theoretical hull speed is just a little under 9 knots (30-50 Hp); you can get her to a little over 10 knot at WOT at least doubling fuel consumption while maintaining that sort of speed. I would settle for a cruising speed of 7-8 knots and use maybe a quarter of the fuel you use at WOT.
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Old 02-03-2010, 05:01   #8
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my Yanmar seems sweet at 1700 for a long range cruise, and 2500 for fast short run. 3800 max but have never pushed it past 3000.
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Old 02-03-2010, 06:56   #9
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My Yanmar manual rates my engine at 3800 max (1 hour out of 12) and 3600 max continious. It also recommends a cruise RPM of 80-85% of maximum continious (2880-3060). I run mine at 2950. Being a cat I have two of course and I get 7 knots with both at 2950 and 6 knots with 1 at 2950. Fuel burn is .75 gallons per hour per engine.
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Old 02-03-2010, 16:43   #10
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You are trying to balance what you want out of the engine and what is good for it. What do you want out of it? Is maximum speed important or is best fuel economy more important? Since an engine has a wide range that it can be run in, you will be determining this range.

Assuming that your gearing and prop are correct, the range that you can run your engine in is quite wide. On the low end, the real danger is wet stacking which is due to low temperatures. As long as the engine is running at temperature, it is fine and does not need to have more load placed on it. For this engine, I would be relatively confident that anything over 1200rpm in gear would be fine but you also won't be going anywhere fast. At the top end, Nick makes a good point on ratings. You definitely should stay within the rated continuous output. Running an engine really hard has detrimental effects and will wear it out more quickly. On a lot of diesels, the reason that they need to be rebuilt is poor compression which will be sped up by running the engine really hard (more cycles at high pressure). The hard parts that actually fail on engines are usually due to fatigue and the two factors in fatigue are number of cycles and stress. The higher you rev an engine, the more cycles it will do. Stress is not linearly related to rpm since you are spreading the additional power at high rpm out over more revolutions. This was a long way of saying you need to put a decent load on the engine but don't tach it out.

So when you combine this with what you want out of it, you can come up with good rpms. It might be that you are concerned about fuel economy most of the time and you decide to run it at 2200 rpm or so. Or maybe you are really concerned with getting places quickly and choose 2800rpm. You can even choose based on the situation. You did mention sound and vibration in your first post and that is important to fine tuning, your setup will work better at some rpms so if you need to change it by 100rpm, do so.
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Old 02-03-2010, 17:34   #11
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Yanmar engine

Thanks all for your comments. I should have mentioned that the engine is a Yanmar 4JH4-HTE, 110 hp, with a continuous rating of 3100 rpm. The boat has a displacement of approximately 290000, and being a Jeanneau 50 DS, has a rather flat bottom. For me, probably speed is more important than fuel consumption so with a hull speed of @ 8.8 kts, I would suspect from your comments that about 2800-2900 should be a theoretical max target which should attain something slightly over 9 kts. I am using a Flexofold prop which is supposed to enable me to attain hull speed with a slightly reduced rpm, Hopefully this boat will sail fast enough so that the above discussion will be for reference only....

Thanks again.

Dick
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Old 02-03-2010, 18:35   #12
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perfect. run it at 80% of continuous for max cruising efficiency. for you that would be right around 2500 rpm.

by the way, I've had flex-o-folds on my last two Yanmars, and they've loved em.
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Old 03-03-2010, 05:06   #13
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Quote:
Originally Posted by klem View Post
Assuming that your gearing and prop are correct, the range that you can run your engine in is quite wide. On the low end, the real danger is wet stacking which is due to low temperatures. As long as the engine is running at temperature, it is fine and does not need to have more load placed on it.
Wet stacking is not common to these engines.
The engine should be under load as soon as oil pressure is stable.

Quote:
At the top end, Nick makes a good point on ratings. You definitely should stay within the rated continuous output. Running an engine really hard has detrimental effects and will wear it out more quickly. On a lot of diesels, the reason that they need to be rebuilt is poor compression which will be sped up by running the engine really hard (more cycles at high pressure). The hard parts that actually fail on engines are usually due to fatigue and the two factors in fatigue are number of cycles and stress. The higher you rev an engine, the more cycles it will do. Stress is not linearly related to rpm since you are spreading the additional power at high rpm out over more revolutions. This was a long way of saying you need to put a decent load on the engine but don't tach it out.
I disagree. The ratings are in place by the engineers to establish operating parameters. The engine can develop more power above the governor settings. Yanmar won't let you go there for various reasons. "Hard" engine use won't lead to excessive wear, light engine use will.
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Old 03-03-2010, 07:47   #14
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Originally Posted by never monday View Post
I disagree. The ratings are in place by the engineers to establish operating parameters. The engine can develop more power above the governor settings. Yanmar won't let you go there for various reasons. "Hard" engine use won't lead to excessive wear, light engine use will.
I agree that the engine is capable of operating well above its stated parameters but they are published because the engineers feel that it is a good guideline for safe operating. I have spent several years modifying diesels (in trucks not boats) and know just how far you can push them beyond stock parameters.

The part that I do not necessarily agree with is about running the engine under a lighter load. Do you mean idle where wet stacking is an issue or do you mean something like 1500rpm on this engine? There is nothing wrong with running an engine like this at something like 1500rpm, it certainly puts less stress and less cycles on the engine. As you rev up more, your boost goes up raising your cylinder pressures which increases. In addition, you inject more fuel raising egt's and many of the engine parts will wear faster at higher temps. The reason that I qualified my statement in the first post saying that the gearing and pitch needed to be correct is that the other large danger of running an engine slow is lugging it but if everything is setup correctly, that will not happen under normal conditions. If there is a reason that I am forgetting that makes lighter load operation bad, please let me know but I hear that comment a lot without any justification.

In truth, this doesn't matter to the OP since they stated above that they were more concerned with speed than fuel economy so they will be running the engine hard anyways.
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Old 03-03-2010, 09:24   #15
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I agree that the engine is capable of operating well above its stated parameters but they are published because the engineers feel that it is a good guideline for safe operating.
engine operating parameters are set to a mix of emissions output, regulated by the EPM, peak HP, and to achieve engine life during warranty and mandatory emissions compliance life.

Quote:
The part that I do not necessarily agree with is about running the engine under a lighter load. Do you mean idle where wet stacking is an issue or do you mean something like 1500rpm on this engine? There is nothing wrong with running an engine like this at something like 1500rpm, it certainly puts less stress and less cycles on the engine. As you rev up more, your boost goes up raising your cylinder pressures which increases. In addition, you inject more fuel raising egt's and many of the engine parts will wear faster at higher temps. The reason that I qualified my statement in the first post saying that the gearing and pitch needed to be correct is that the other large danger of running an engine slow is lugging it but if everything is setup correctly, that will not happen under normal conditions. If there is a reason that I am forgetting that makes lighter load operation bad, please let me know but I hear that comment a lot without any justification.
idle is not a condition of load. load is achieved my engaging the transmission in gear, heavy alternator or refrigeration operation. You must put mechanical resistance on the rotational force of the crankshaft to be considered load.

Running an engine at idle, or even high idle of 1500 rpm. Does nothing to increase cylinder pressures and temp. You need these to make the engine thermally stable. And make the rings expand to the cylinder walls. All too often we see stuck rings or glazed cylinders from inadequate load.

Quote:
In truth, this doesn't matter to the OP since they stated above that they were more concerned with speed than fuel economy so they will be running the engine hard anyways.
that is correct
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