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Old 04-01-2013, 12:11   #31
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Wink Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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Originally Posted by donradcliffe View Post
This may work on a big ship, but it won't work on a boat diesel unless you put another cup on the return line. Messy and a lot of work.
On my engine the return line goes back to the filter as on many other engines.
Just close the valve at the fuel tank and disconnect it there. If on your boat the return line goes back to the tank. Which is not unusual and always done for pump injectors (like on Cummings engines) Then you would indeed need to disconnect both lines. Its still not that hard.
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Old 04-01-2013, 12:39   #32
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

general rule for idle is engine HP/1000=GPH burn. in you case 30/1000=.03 GPH. .05 was mentioned and its probably between the two numbers.
in any case its a very small amount compare to cruising consumption. if you have to charge using your main engine I would vary the rpm while charging and not let it sit at the same speed for long periods.
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Old 04-01-2013, 13:11   #33
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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Originally Posted by Jim Cate View Post
Aw come on guys! The OP asked a reasonable question and all he has gotten in return is slagging his practice of low speed battery charging.

Does anyone have any data about the fuel consumption of typical small marine diesels at idle speed, either no load or small (alternator) loads?

I would like to know too!

Cheers,

Jim
Yeah.... we've been down this road before and everyone has their opinions. Truckers idle their engines for hours upon hours and get more hours per engine than any sailboat does.. Many cruisers for many years have used the Diesel aux for battery charging.
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Old 04-01-2013, 13:17   #34
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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Originally Posted by chrisferro View Post
Take a look at this link:

http://www.yanmarmarine.com/theme/ya.../PDF/3YM30.pdf

It looks like about 1/3 of a gallon at idle and almost 2 gallons per hour at max rpm. But, yeah, you should never run a diesel at idle for long periods of time - only to warm it up. Put a load on it, like let out a bunch of scope, shift it into reverse and throttle up a bit.

Happy New Year!
I would say there is something wrong with that chart. It seems to range from 1 gal per hour at ~1500rpm to almost 2 for a 30hp Yanmar. My experience is less than half of that.
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Old 04-01-2013, 13:38   #35
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

Efficiency of diesel engine = 30%
Power transferred to alternator = 10%
Efficiency of alternator = 50%

Result = 1.5% efficiency. Hope you used your electricity well! Enjoy oil while it lasts...
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Old 04-01-2013, 14:54   #36
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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Originally Posted by Cheechako View Post
I would say there is something wrong with that chart. It seems to range from 1 gal per hour at ~1500rpm to almost 2 for a 30hp Yanmar. My experience is less than half of that.
You are probably putting less load on it....
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Old 04-01-2013, 17:19   #37
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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So of all the people who have posted here No one knows how much fuel they burn to charge their batteries?

Astounding!

So no one here knows who many weeks or months they could remain on the pick charging by engine?

So no one here knows their maximum sailing passage by fuel consumption?

I am amazingly astounded. For such a penny pinching mob of let's live on 2 cents per month we don't know how much the big noisy donk costs us?

In fact I might be the only person who knows their cruising speed consumption.... 4 Gerry cans per 48 hours at 1800 revs.

Someone here must have their own figures not just Yanmars (which I can't find for the 4jh3e)


Mark
Avast that astonishment, Mark!

Can't speak for others, but we have a very good idea of fuel consumption when driving the boat (2.5 to 2.9 L/hr for normal cruise, depending on sea state and bottom cleanliness) at 6 knots which is our usual motoring speed. We have done this for enough hours to make the calculations reasonably accurate.

But, we don't have such a history for battery charging, which we only do in adverse conditions... heavy overcast, little wind, short days, etc. And we have no knowledge at all of usage at unloaded idle (admittedly, this is more a curiosity than a real need for knowledge!).

I agree with those who say that the best way to determine these things is to measure usage directly. However, I'm not in a financial situation where Dockheads thousand dollar flow meter is likely, and the mess and work involved in disconnecting supply and return fuel lines and making the trial runs whilst holding various containers is daunting to me... so asking the above questions seems reasonable!

BTW... how much fuel does a "Gerry" can hold?

Cheers,

Jim
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Old 04-01-2013, 17:43   #38
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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BTW... how much fuel does a "Gerry" can hold?

Cheers,

Jim
19 litres to the line. That's 5 gallons...

There is some dude Agent in Egypt whose ears are still ringing from the abuse I gave him for trying to rip me off. An inch under the line and claimed it was 21 litres. I don't think he claims much any more
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Old 04-01-2013, 20:56   #39
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

Do you realize that Mr Edwards (assumption) probably doesn't really care as he hasn't responded since his OP on the 1st.
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Old 04-01-2013, 21:21   #40
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

.8 gallons an hour powering at 1500 rpms, 6 kts. I don't know how much I use at idle or at 1200 rpms when charging because if it's sunny and we're not greedy we don't need to run the engine with 570 watts of solar panels above the cockpit.
If we're greedy I only need to run the engine for 2-3 hours a week and I can't measure accurately enough to tell you what that takes because the boat's usually moving at anchor and the dipstick doesn't tell you much if you're rolling.
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Old 05-01-2013, 10:46   #41
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

I record a continual fuel bought/engine hours.... so I know the overall usage. But who cares how much at idle vs whatever? Just keep the tank as full as possible when it's easy to get! It's island time man!
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Old 06-01-2013, 10:23   #42
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

Ladies and Gents . . .
. . . who responded to my original post and question . . . I just want to say thanks! I am on the internet on land via WiFi for the first time since my post, and therefore it is much easier to respond.
Results: Found the engine fuel consumption curve on the Yanmar site. Thanks. Also trying the "light load in reverse" on the diesel when charging, and that seems to work OK, too. Thanks. Also using the portable generator now for daily battery charging. However, obviously I do not have the correct charger to plug into it, as my little 4Ah charger takes forever to give any juice to the batteries. I either need to buy a new charger for the portable generator, or figure out how to connect the portable generator to the built-in AC charger on this boat? This latter solution might be the easiest, if feasible?
I keep learning from everyone's comments.

Again, many thanks.

JEdward
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Old 06-01-2013, 16:40   #43
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My fuel burn at anchor is .... 1 liter per hour. That is mostlyl charging at 1200rpm with a tiny bit of motoring to the fuel dock, re-anchoring and the like.

The above posters are correct in writing that fuel burn is mostly dependent on load not rpm.

Beta 38hp diesel. 100A alternator usually running at about 50A.
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Old 06-01-2013, 17:30   #44
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Re: Diesel Fuel Burn: Idle vs. 3/4 RPM?

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My fuel burn at anchor is .... 1 liter per hour. That is mostlyl charging at 1200rpm with a tiny bit of motoring to the fuel dock, re-anchoring and the like.

The above posters are correct in writing that fuel burn is mostly dependent on load not rpm.

Beta 38hp diesel. 100A alternator usually running at about 50A.
AHAA! Some data from the real world.

Thanks, Daddle.

Cheers,

Jim
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