Fuel consumption on a Yanmah 4JH3E 2003 model

[Akapeterc]

I just recently did a trip involving approximately 50 hours of motoring and my fuel consumption at 2800 rpm has worked out at 3.4 L per hour. Has anyone else got similar fuel measurements on the same motor we have a 2003 Hunter 44DS.

[Paul L]

That seems a bit low. We consume at that rate when running closer to 2100 rpm. Take a look at the fuel consumption chart in this spec
http://kp44.org/ftp/Yanmar_4JH3-TE_Datasheet.pdf

[Akapeterc]

Ours is not a turbo

[Paul L]

Originally Posted by Akapeterc

Ours is not a turbo

So find the Yanmar data sheet for your model

[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.

[jamhass]

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.

Suggests the engine is not at its working load (at that rpm) indicating the boat is under-propped.

Can you get to hull speed?

[kenbo]

Originally Posted by jamhass

Suggests the engine is not at its working load (at that rpm) indicating the boat is under-propped.

Can you get to hull speed?

Correct. Fuel usage is more aligned to engine load then it is to RPM. The OP's fuel usage isn't completely out of line.

[foxfire]

Not that it’s really applicable to your specific boat and question but a very good rule of thumb for any Diesel engine is 1 gallon per hour per 20 horsepower actually delivered to the water.
So rpm and prop size and pitch will effect what you burn but assuming your prop is matched properly (pun intended) To your engine you will deliver full rated power at full rpm. props take power as a square relation to shaft rpm. If you have a 40 hp engine running at full rated rpm you would burn 2 gallons per hour. If you ran at half rpm you would only use about 1/2 gal per hour. This shows the big cost of that extra speed, since most cruisers will move at 3/4 of max speed with half rpm!, and 1/4 the fuel!

[kenbo]

Originally Posted by foxfire

Not that it’s really applicable to your specific boat and question but a very good rule of thumb for any Diesel engine is 1 gallon per hour per 20 horsepower actually delivered to the water.
So rpm and prop size and pitch will effect what you burn but assuming your prop is matched properly (pun intended) To your engine you will deliver full rated power at full rpm. props take power as a square relation to shaft rpm. If you have a 40 hp engine running at full rated rpm you would burn 2 gallons per hour. If you ran at half rpm you would only use about 1/2 gal per hour. This shows the big cost of that extra speed, since most cruisers will move at 3/4 of max speed with half rpm!, and 1/4 the fuel!

Not to split hairs but I believe the number is 17hp per US gallon for a perfectly matched engine/reduction/propeller system.

To the OP, when you fully open the throttle, what is the rpm reading on your rev counter. And have you ever checked the accuracy of your rev counter? All important when accessing fuel consumption questions.

[foxfire]

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

[canyonbat]

Here are some graphs I created using Yanmar published data and actual speed readings at various RPMs on our 4JH5E engine. Actual consumption was always 10% or so lower than the charts. 2011 Beneteau Oceanis 40

[kenbo]

Good catch...we should just be using the metric units like the OP. 17HP/3.78l or 20HP/4.55l

[JD-Odyssey]

We have a 2004 Hunter 41 and the same engine. Your fuel consumption is pretty close to ours...

[Gregg927]

I have the same engine on my 43 ft ketch, 28,000 pounds. At 2800 rpm my typical consumption is 0.8 gallons per hour; typical speed is 6 to 6.5 knots.

[StuM]

Originally Posted by Gregg927

I have the same engine on my 43 ft ketch, 28,000 pounds. At 2800 rpm my typical consumption is 0.8 gallons per hour; typical speed is 6 to 6.5 knots.

What sort of gallons?