Fuel consumption on a Yanmah 4JH3E 2003 model

[a64pilot]

Originally Posted by StuM

3.4 lph @ 2800 is quite a bit lower than expected. The fuel curve for that engine is around 3.4lph @ 2400 and around 5lph @ 2800.

Stu, where did you get a graph like this which has fuel consumption on it?
Think you can find one for a 4JHE ? I have looked and can’t find one with gallons per hour like that

[sailorboy1]

My tach long ago died

0.65-0.7 gah at 6 knots speed

[StuM]

Originally Posted by a64pilot

Stu, where did you get a graph like this which has fuel consumption on it?
Think you can find one for a 4JHE ? I have looked and can’t find one with gallons per hour like that

That comes from the JH3 data sheet here: https://www.simplicity-marine.com/pdf/Yanmar/JH.pdf


Sorry, haven't located one for 4JHE.

[StuM]

Originally Posted by a64pilot

Stu, where did you get a graph like this which has fuel consumption on it?
Think you can find one for a 4JHE ? I have looked and can’t find one with gallons per hour like that

I did find a set of specs for the 4JHE which gave sufficient info to calculate theoretical consumption (which should be fairly close). http://www.marx-ftp.de/Downloads/Mar...E_englisch.pdf

[Gregg927]

Diesel gallons! .... Just a joke reply, my measurements are US gallons, pounds, rpm, feet, etc. I too wish we would join the rest of the world in our metrics.

[StuM]

Originally Posted by Gregg927

Diesel gallons! .... Just a joke reply, my measurements are US gallons, pounds, rpm, feet, etc. I too wish we would join the rest of the world in our metrics.

We could have guessed that if you had put some information such as your location in your profile

[hamburking]

Originally Posted by foxfire

Yes, though us Canadians use the imperial gallon eh?

YES! Bigger gallons means more miles per gallon!!! Just one more reason its great to be Canadian!!!

[a64pilot]

Originally Posted by StuM

I did find a set of specs for the 4JHE which gave sufficient info to calculate theoretical consumption (which should be fairly close). http://www.marx-ftp.de/Downloads/Mar...E_englisch.pdf

Great, got it. I suck at math and do stupid things like displace decimals etc.
That chart correlates well with my fuel consumption, mine is a little higher than the chart, but I’m a little overpropped too and that would account for the extra fuel burn.

[edguy3]

@StuM

how did you come up with the HP data in your spreadsheet?

thanks
/ed

[StuM]

Originally Posted by edguy3

@StuM

how did you come up with the HP data in your spreadsheet?

thanks
/ed

I've posted this in previous threads
The standard formula uses the theory that HP varies by the Cube of the ratio between RPM and Max RPM. i.e.

HP = MaxHP * (RPM/MaxRPM) ^ 3

That's reasonably accurate for most diesel engines under normal operating conditions.

It's also reasonably true that fuel consumption is fairly constant per HP over the general operating range of a marine diesel engine which is appropriately propped.

In the attached screen cap, the cursor is on C9. The yellow cells are direct value inputs for the specific engine ( you can pretty much leave D2 and D3 fixed for most normally aspirated diesel engines and diesel fuel)

[a64pilot]

Actually if you look, BSFC does vary with RPM, the sweet spot for a 4JHE being between 2600 and 2800 RPM, but it doesn’t amount to a whole lot.
ALL little Diesels are actually very close on fuel consumption per HP, there just isn’t one model that is lots more efficient that the rest.
Using Stu’s method will get you very close

[edguy3]

Fantastic! I put the formula in google sheets and have shared it here: SHEET

Thanks
/ed

[StuM]

Originally Posted by a64pilot

Actually if you look, BSFC does vary with RPM, the sweet spot for a 4JHE being between 2600 and 2800 RPM, but it doesn’t amount to a whole lot.
ALL little Diesels are actually very close on fuel consumption per HP, there just isn’t one model that is lots more efficient that the rest.
Using Stu’s method will get you very closeAttachment 160319

Yep, using consumption at MaxRPM gives you a small safety margin at cruising speeds.

[pcmm]

Originally Posted by foxfire

Yes, though us Canadians use the imperial gallon eh? Good point about tachometer accuracy

Actually us "Canadians" use the US gallon when measuring not the Imperial gallon. Can't remember the last time I saw anything in Canada referenced to the imperial gallon, so much so that I had to look up the conversion (4.54l) everything is compared to the U.S. gallon (3.78l)

Anyway fuel consumption is also related to displacement also! our boat ( OI 41 ) displaces around 28,000lbs and when we cruise at 22-2500 rpm we go through around 1gal per hour. when we cruise at 27-2800 we use around 1.3gph.

[StuM]

Originally Posted by pcmm

Anyway fuel consumption is also related to displacement also! our boat ( OI 41 ) displaces around 28,000lbs and when we cruise at 22-2500 rpm we go through around 1gal per hour. when we cruise at 27-2800 we use around 1.3gph.

Only in so much as displacement affects the RPM required to motor at a specific speed. A much lighter boat with the same engine would go through the same fuel at the same RPMs, but it would probably attain greater speeds at those RPMs.

i.e:
the greater the displacement, the greater the drag;
the greater the drag, the greater the HP required to move at a given speed;
the greater the HP, the greater the fuel consumption
(which brings us right back to the formula above.