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Old 01-09-2017, 12:57 PM   #1
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Are you running your small diesel too hard?

Interesting article from Seaboard Marine. It claims that if you run more than about 2 GPH per liter of engine size you will not get many hours out of these small diesels.

I burn about 2gph with my small 2 liter Yanmar, so about one gallon per liter, so I guess I'm Ok, if this article is correct.

Continuous Duty - A Different Perspective - Seaboard Marine
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Old 01-09-2017, 02:06 PM   #2
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Reading Tony's article, the easy math is....

As measured at the fuel dock fuel used divided by engine hours = average GPH

Average GPH divided by WOT GPH = Duty Cycle

We have Cummins BTA5.9 engines rated at 330 HP each.

Our average GPH per engine is right at 4.5. That is based on fuel dock numbers divided by engine hours.

The WOT rated fuel consumption for our engines are 16.8 GPH

4.5/16.8 = 26.8% duty cycle

If we look at the fuel consumption per liter we take 4.5GPH and divide it by the displacement in liters (5.9) so 4.5/5.9 = .76GPH per liter of displacement.
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Old 01-09-2017, 02:32 PM   #3
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Keith,
"As measured at the fuel dock used divided by engine hours = GPH."

That's why so many post unbeliveable numbers re fuel burn. All the hours running slow, anchoring, warming up ect ect burn much more fuel than most people belive.

I'm of the opinion that a very long trip being careful to record the times (rpm and minutes) of lower than cruise emgine load is the best way of getting close to real fuel burn. It's not that important to me like perfect navagation ect.

Or use hp/hour specs available for most all engines in conjunction w max fuel burn as stated by the manufacturer.
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Old 01-09-2017, 03:02 PM   #4
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Tony may be a bit conservative with his rule of thumb. 2 gph is roughly 35 hp per liter. That is Tony's assessment of the maximum most marine engine manufacturer's consider their engines to be suitable for continuous commercial duty.

But that doesn't mean you can't get thousands of hours (if properly maintained) out of an engine if you run, at say 45 hp per liter. That is my personal maximum.

Look at DDs on fast sportfishers. A 6-71TI can produce 485 hp and sportfishermen run them hard, maybe 400 hp continuously or 68 hp per liter. These often need rebuilding at 2-3,000 hours. Kind of like getting a new BMW when it approaches 75,000 miles.

So it is all a continuum. Lower load means longer life. You pays your money....

And that rule of thumb really is only applicable to turbocharged, after cooled engines that make 50 hp per liter or more. Those engines have after cooling which provides cooler air to the cylinders, more cooling system headroom, piston oil jet cooling and better valve metallurgy. All of which let them make higher hp continuously.

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Old 01-09-2017, 03:27 PM   #5
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I would guess that few on this site run their high HP small displacement diesels very hard. Maybe folks with planing boats do.
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Old 01-09-2017, 03:40 PM   #6
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"Interesting article from Seaboard Marine. It claims that if you run more than about 2 GPH per liter of engine size you will not get many hours out of these small diesels."


I generally agree with this as one component of 2 that will let any of these 4 stroke TA engine live a very long life. Tony has been publishing this message for over 10 years and IMHO he has been right on target for the majority of users out there.

What he is really saying is that when your 4 stroke TA engine(s) are under high cruise you should not let them load above 1 hp per every 2 cubic inches or 30 hp per liter. For a typical 5.9 liter Cummins that would be a high cruise utilizing about 180 hp or less or a fuel burn in the area of 9.5 to 10.5 gph or less.
He is not referring to an average fuel burn across engine clock hours but rather a 'self imposed' limit on engine loading.
The second part of the equation is to make sure that your 4 stroke TA engine will reach its rated rpm +3-5% on a fully loaded boat on a hot and humid day as a brief test.
If you can reach rated +3-5% and run at or less than 30 hp per liter you will see a long engine life.
For those that run EGT and boost gages on these engines they will see some real gage results if you fall outside these general guidelines.
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Old 01-09-2017, 03:44 PM   #7
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"Look at DDs on fast sportfishers. A 6-71TI can produce 485 hp and sportfishermen run them hard, maybe 400 hp continuously or 68 hp per liter. These often need rebuilding at 2-3,000 hours"


David - For the most part I do not see a realistic way to compare two stroke diesels with the 4 strokes. And I see and know many 2 stk DD users who would not necessarily agree with running those engines at those limits either.
Of course I do know a number of sport fisherman that run DD's out of Montauk and BI over the summer at tournaments that do run at those levels - and their mechanics love them for it as it keep them in business.
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Old 01-09-2017, 04:17 PM   #8
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Eric,

I can come close to your means of calculation, but I didn't record times/rpm. In 2016, we covered 2471 statute miles, used 720 gals of fuel, in 354.9 engine hours. That broke out to 2.03 gph on a Cummins 6CTA8.3-M2. That's a calculated loading of 8.6% using WOT fuel consumption of 23.6 gph.

The engine is 21 years old with 5308 hours on it, 500 of those since we took delivery in Aug 2015. I'm in Tony's light loading school. A couple of times over the summer I took it up to WOT for a few minutes to check cooling and turbo boost. According to Cummins, I can run at 2400 RPM for extended periods, but the fuel consumption is so high along with the wake, we drop back to 1200-1400 and keep it there.

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Old 01-09-2017, 06:03 PM   #9
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I have the same 6CTA engine rated M1. Technically, I can run it WOT for 24 hours a day but the noise and the fuel consumption is breathtaking. 35 hp per litre is about 250 hp which is my M1 rating. I like 1400-1600 best too.
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Old 01-09-2017, 06:59 PM   #10
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I usually burn between 3.4 and 3.6 litres/hour (less than a US gallon/hr) for my 1.8 litre Vetus/Mitsubishi engine, so I am well under.
It's a common sense statement, really. He's basically saying "If you run your engine flat out, it won't last long" Most engines are built since way.
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Old 01-09-2017, 08:34 PM   #11
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My cruise speed is one knot below hull speed (1800 RPM vs. maximum of 2400, while reaching hull speed at 2200 more than doubles fuel consumption). Good fuel mileage, and especially, the engine runs "happy" at near 40 percent load.
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Old 01-10-2017, 01:58 PM   #12
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3.1 GPH, 393 ci, na hino. This is the average since 2010 and 600+ hours includes generator time. I typically cruise around 1200-1400 rpm with the occasional 2600-2800 rpm run to make a lock or just to check that everything is working as it should, 3000 rpm is wot.
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Old 01-10-2017, 02:05 PM   #13
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I run my 450hp 6CTA 8.3 at 1800-2100 for 16-21kts. At 2000 it is burning 11gph so about 220hp going down the shaft line. So 26hp/liter or 1.3gph/liter. Looks pretty good.
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