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Old 02-01-2014, 09:50   #1
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Fuel Consumption on Yanmar ...

Gentlemen thanks in advance for your opinions and advice, the answer to this question will lead me to quite a few more.
I am wondering about the fuel consumption of my 1980 yanmar straight six turbo, no figures from manufacturer.
95 h.p. pushing (reported from builder) 50 ton dry weight 13.5m lwl dive boat.
Huge hours, runs like a top, but I cannot get my head around using 25 liters or more then 6 gallons per average running hour at 1700 rpm sweet spot to make 95 h.p. Redline seems to be around 1900.
Theoretical hull speed 8.6 knots getting 6.2 @1700.
No smoke, a tiny bit of blowby from the breather.
I was wondering if this amount sounds right ?
Photos.
https://dl.dropboxusercontent.com/u/.../Boat/boat.jpg
https://dl.dropboxusercontent.com/u/...oat/engine.jpg
As always, newbie grateful for assistance.
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Old 02-01-2014, 10:00   #2
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Re: Fuel consumption on yanmar..

This page might give you the information you need.
They say that you will burn 1 gal per 20 hp, so approx. 5 gals per 96 hp.

Diesel Engine Fuel Consumption - Quick calculation

Your fuel burn might be a little high but it could be the quality of fuel that you are burning, the cleanliness of the boats bottom, the prop, etc.

I just realized that is UK site so if you quoted 6 us gals. that would be right on the money.
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Old 02-01-2014, 10:09   #3
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Re: Fuel consumption on yanmar..

Well if you figure around 15 hp per gallon of fuel per hour..... 95 hp divided by 15 = 6.333333 Seems like fuel burn is in the ball park to me.

"Redline seems to be around 1900. " ??? What does Yanmar list as min installed RPM under load for that engine? If you are saying the most RPM the engine will turn with that prop is 1900RPM and the book says it should turn max RPM of 2700 RPM you are over propped.
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Old 02-01-2014, 10:18   #4
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Re: Fuel consumption on yanmar..

My calculations which use cubic propellor curves and other Bebe specified formulas shows your boat (50 short tons, 44 foot LWL, 15 foot beam - single engine) needs the following:

53 HP to move at 6.6 knots - 2.9 GPH diesel
75 HP to move at 7.2 knots - 4.1 GPH
92 HP to move at 7.5 knots - 5.1 GPH

The fuel burn rates above use a BSFC specification of .055 gallons/HP/Hour (0.39 pounds/HP/Hour) which is what my Yanmar 4JH2E (normally aspirated) manual specifies

Increasing the displacement to 60 long tons to account for fuel, water, customers shows the following results:

53 HP to move at 6.2 knots - 2.9 GPH diesel
91 HP to move at 7.2 knots - 5.1 GPH
122 HP to move at 7.5 knots - 6.2 GPH

Weight makes a huge difference!
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Old 02-01-2014, 10:27   #5
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Re: Fuel consumption on yanmar..

Hello Darylat:
Thanks very much.
The manual I have is in Japanese, the plate on the engine says 1600 r.p.m. but we know it has been changed as it also says about 30 H.P. 30 h.p. is not gonna move that boat at 6 knots !
I have no solid numbers from the manual, so we are running by feel...
it revs to 1900 in gear and starts to smoke at about 7 knots.
1700 is a very sweet spot and and 85* of full load. (As determined by the smoke)
It was over propped previously with three blades at 1.02 meters, smoked bad when throttle was opened, you could feel it struggling.
Swapped it out for 92 Cm. and it runs really sweet.
Sorry if I confused you, new to a lot of these terms.
I was looking for just the kind of guideline you gave me, x number of gallons per h.p. per hour, seems we are spot on the numbers...More questions to come. Thanks
Larry
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Old 02-01-2014, 10:31   #6
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Re: Fuel consumption on yanmar..

Tacoma and Deepfrz:
Thanks for filling in the details. Very happy to hear that we are good in the fuel consumption department, yes it is U.S. Gallons.
Much more to come now that I know this.
More to come !
Thanks again !
Larry
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Old 02-01-2014, 10:38   #7
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Re: Fuel consumption on yanmar..

OP,
You state: "I am wondering about the fuel consumption of my 1980 yanmar straight six turbo, no figures from manufacturer. 95 h.p. "

Looking at Yanmar historica data - I find no 6-cylinder Turbo Yanmar that makes less than 250 HP. The old (1988) 4-cylinder turbo diesel Yanmar made 110 to 140 HP.

The first 6-cylinder Yanmar that I can find was the 6LY-UTE at 315 HP which was produced 1992 - 1997.

Of course the boat builder could have marinized an old Yanmar tractor engine and put it in the hull. About eight years ago I did a west coast delivery on an 69 foot boat with a 40 year old Puget Diesel that had been custom marinized and dropped into a boat that was finished in 2005. 10 liters and 150 HP - but lots of torque!

Are you sure about the engine specs?

Here is a great web site that shows the history of Yanmar diesels and how to decode the serial numbers:
http://shop.toadmarinesupply.com/mar...entification++
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Old 02-01-2014, 10:50   #8
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Re: Fuel consumption on yanmar..

If you are concerned about the amount of fuel you are using try dropping the engine speed down about 50 rpm and see what difference that makes. It may make a very big difference.
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Old 02-01-2014, 15:42   #9
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Re: Fuel consumption on yanmar..

Hi Guys;
I wanted to keep the post short so I left out a mountain of details.
Yes definitely and with out a doubt yanmar straight six turbo from the factory.
1980.

See attachments.
I have the Yanmar shop manual in Japanese and some how the parts book in English.
Domestic model only, Mac boring had never heard of it.
I have even had an email from one of the engineers that designed it.
Heat exchanger in the block, water pump">raw water pump mount is part of the block, zincs everywhere.
PTO on the front to run hydraulic motor to pull up fishing nets, yanmar marine gearbox in your choice of three reductions.
Attached Thumbnails
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Old 02-01-2014, 16:00   #10
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Re: Fuel consumption on yanmar..

Not concerned so much about fuel consumption, but overall health of the engine and if it was in particular an inefficient design.
I want to get a spare, rebuild this one.
I think the engine is IDEAL for my needs, but having no idea of efficiency I did not want to plow a lot of money in a spare engine, and a rebuild of this one. If it was an inefficient design.
BTW, 31,000 hours....no smoke, minimal blowby, starts every time, within a half second. Rod bearings are starting to show copper. Pistons are beautiful....It weighs about 1500 pounds with gear box, and how do I know the bearing condition without pulling it apart ? It is SO BIG, there are access doors into the crank case and each cylinder has its own head, I can pull a head, cylinder and rod out in about 45 minutes.
Crazy stuff for 95 H.P.!
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Old 03-01-2014, 09:08   #11
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Re: Fuel consumption on yanmar..

Quote:
Originally Posted by DeepFrz View Post
If you are concerned about the amount of fuel you are using try dropping the engine speed down about 50 rpm and see what difference that makes. It may make a very big difference.

I concur with this. I found a speed/power setting that seemed comfortable on my boat. Then when we were travelling on the Great Loup I put enough miles on the boat to get a good handle on fuel burn by going at least fifty hours on a specific power setting and then topping the tanks. I wound up at a speed .5 knots slower than initially used and save more than 20% of fuel burn.

Looks like a serious work horse of an engine.
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Old 03-01-2014, 10:36   #12
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Re: Fuel Consumption on Yanmar ...

"BTW, 31,000 hours....no smoke, minimal blowby, starts every time, within a half second. Rod bearings are starting to show copper. Pistons are beautiful...."

It is nice to hear about the hours and conditions.

In early 1995 the Tacoma, WA Yanmar dealer sent a mechanic over to my sailboat to check on a minor issue with my new 4JH2E. That mechanic told me the shop had been maintaining Yanmar engines in commercial fishing vessels for many years. He said that they were absolutely bullet proof and would run forever if the owner did three things properly.

- keep the fuel clean
- keep the air clean

those are normal diesel operating standards and did not surprise me

He then said the third was most important for sailboats

- run the engine HOT and HARD

He said all the Yanmar problems the shop dealt with were due to lightly loaded slow running engines that had built up carbon and fouled their injectors

He said Yanmar wanted their engines to run at 70% - 80% of their 24 hour RPM limit and could do so endlessly. He was adamant that I had to run my engine up to 2900 RPM for at least 5-minutes once every 5-hours.

So far has worked well for me
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Old 03-01-2014, 19:50   #13
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Re: Fuel Consumption on Yanmar ...

Hello Tacoma and all who have been kind enough to put me on the right track.
Well I have to concur with that yanmar mechanic.
30,000 + hours, 2,000 with me. I am sure it was run hard all its life and we do run it hard.
I have been hearing to run it hard from day one of my unexpected being a boat owner.
This engine is indeed ideal for my purpose, fast enough when run hard....I do not want to put 150 to 300 h.p. into it, only to burn more fuel or run the engine to easy.

I will likely never invest the time to accurately measure fuel consumption, as the boat is loaded with 3 people and sometimes 20 people and 2000 pounds of scuba tanks and gear. Big performance hit there in any case.
Fuel is a cost of doing business for me and while economy is important, more importantly is durability. If that engine goes down, I am closed for two months.
That it is running in the normal fuel consumption range tells me it is worth trying to find another, and keeping a spare.
Thanks again.
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