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What are the pros/cons of using one engine at a time to idle out offshore in order to save fuel? I am thinking of doing this by leaving Fri evening in order to be in blue water by dawn.
I think there are two main parts to this:
First, where can I find fuel consumption rates at low rpm for 375hp 3208TA Cats? It should then be an easy matter of comparing speed and burn rates to see if it would even be worth looking at further.
Second, what risk of damage is there to the 'other' engine and transmission from the prop's being spun by the water? If that is a problem, can I solve it by just putting that engine in gear?
Most diesels are not overly fond of long idling times, particularly under load. Matter of fact, most diesels manufacturers recommend you run them for (at least) 10% of the time at full throttle with optimum cruise being at 90% of full throttle. Less than this can cause a lot of carbon deposits and other nasty stuff to happen.
As far as the transmissions are concerned, if you are to run one motor only, I would suggest using a strap wrench to tie down the shaft on the non-running motor to prevent it from "free wheeling". Some transmissions will not provide lubrication unless the motor is running.
I am not sure if the loss of sleep and potential damage to your engines and transmissions would be worthe the fuel savings you can expect to see. I would go to the boat diesel web site (often referred to on here) for more specific information.
You have a boat with twin Cat 3208's. You shouldn't be worrying about the price of fuel. If it's a financial hardship on you...then sell the thing and take up golf.
Geez...
BTW-Invest in a fuel mgmt gauge. It'll tell you everything that you want to know.
Diesel engines are not governed by a air/fuel mixture like gas engines, so at no-load idle a diesel is only consuming enough fuel to overcome friction and inductive loads (i.e. alternators). Very little fuel for that matter.
What happens at these low rpm's is that engine is actually cooling, so the injection of diesel is not being completely burned. This can lead to carbon deposits but worse, diesel is condensing on the cylinder walls and eventually mixing with engine oil. At 19 to 1 compression ratios you don't want a diluted lubricant running through the engine.
You can idle it until the cows come home, you just need to bump the idle a bit.
You have a boat with twin Cat 3208's. You shouldn't be worrying about the price of fuel. If it's a financial hardship on you...then sell the thing and take up golf.
Geez...
BTW-Invest in a fuel mgmt gauge. It'll tell you everything that you want to know.
Never heard the "run them at full throttles" advice. I've run mine at wot once for 5 minutes maybe 3 years ago. I know that diesels like to be run hard but what's the advantage of running them at wot for 10% of its running time?
Won't running them at "cruise" burn plenty of carbon out of those cylinders?
From my understanding you should run them WOT once every couple of months for a few minutes. This is for several reasons, one being that it clears up any built up carbon etc, diesels are meant to work hard so this won't do any damage. Prob the most uesful reason is to check up on your motors. Run them w/o the eng. sync on and make sure that both motors are performing similarly, ie close to same RPM, they are actually reaching their rated max RPM, make sure the cooling system is working well. You should keep trac of what your speed, RPM, temp, oil pressure are for each time you do this so that you can compare the results. Be sure that each time you have the same load, ie full fuel and water. Major problems with diesel engines will effect the engine's performance before the failure leaves you stranded. You may or may not notice these signs if you never exceed cruising speeds. Take into account bottom growth too, if its been awhile since you have the bottom redone and there is some growth, don't worry if you lose a knot or two of speed.
I know about running the diesels at WOT, I usually do it in the bay on the way back in as recommended for the 'health' of the engines as well as to check performance for any indications of a problem.
As for the cost comments: Though I can afford the fuel I am asking this question because #1, if it is more efficient w/o significant downsides why on earth would I waste the fuel? and #2 if we're taking a long trip out there I don't want to limit myself unnecessarily by fuel capacity.
Thanks anyway, I'll check on boatdiesel.
steveyacht - 2/2/2006 2:17 PM
Most diesels are not overly fond of long idling times, ...
Makes me wonder why so many truckers leave their engnies running at rest stops? Buses too?
Truckers leave their engines running while they eat because they are ahead of time on their logs, which are monitored along with the engine hour meters and odometer. Those logs are checked by the highway patrol to determine the vehicles speed and driving time of the driver. Essentially, they eat while the truck is "on the clock" for the log books. If they are ahead of schedule due to speeding, they can use that time to eat. If the hour meter was off, they could be nailed for speeding.
steveyacht, yes diesels love to be run but they do not recc you run at wot 10% of the time the say you can also
you can run at 90% wot 90% of the time some say you can but you got to rember these are the limits not what you should do . remeber we (I) are talking about pleaser craft not heavy duty engines ( low hp per c.i. )the same brand engine & type can fall in to both types like a 671 DD at 200 hp you can run at near wot for ever no proplem at 485 hp
it would not last long at wot . my 300 hp 6bta cummins are run at 2200-2400 rpm cruse rated 300 hp at 2800 ( will turn 2900) I would never think of runing them at near 2800 for any lenth of time ( a few minites fine )
you will get back from you engines what you put in ! they do have ways to get even . I hope my cummins out live me
and I am not planing on going anytime soon
Paul
My new FL80 frieghtliner at work has a IL6 7.4 liter electronic Cat motor the book say's not to idle for more than 5 min. that's enouhg time for engine cool down.
Alot of these new diesel's are now LOW OIL PRESSURE engine's and at a 700 rpm idle the motor starts to eat it self , if you bump the R's up to about 1100 or 1200 rpm's the OP comes up and they can idle all day long .
Same goes for your power strokes, duramax's and cummen's.
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Truckers leave their engines running while they eat because they are ahead of time on their logs, which are monitored along with the engine hour meters and odometer. Those logs are checked by the highway patrol to determine the vehicles speed and driving time of the driver. Essentially, they eat while the truck is "on the clock" for the log books. If they are ahead of schedule due to speeding, they can use that time to eat. If the hour meter was off, they could be nailed for speeding.
Not true, log books dont use engine hours.
Most drivers leave their engine running 24/7 and get over a million miles before a rebuild. Big truck engines are built for this. If it is 10 degrees or 100 degrees and you are sleeping in your truck you leave it running. Walk through a truck stop parking lot at night it sounds like an airport runway.
Our mechanic has put idle time 5 minutes signs on the dash of our two new straight trucks.
Location: Los Angeles, FL.or Georgia, depends. In Fl now.
Posts: 5,979
Re: Diesels idling on one engine to save fuel?
Quote:
steveyacht - 2/2/2006 1:17 PM
Most diesels are not overly fond of long idling times, particularly under load. Matter of fact, most diesels manufacturers recommend you run them for (at least) 10% of the time at full throttle with optimum cruise being at 90% of full throttle. Less than this can cause a lot of carbon deposits and other nasty stuff to happen.
SNIP!.
You sure your not talking about a 2 stroke classic?
Amen ears and I guess just simply smoke up on that crack pipe there "watercop". I have driven an international for a while now and I leave it idleing most of the day that I'm not in it. I do bump up the rev limiter to a grand or so when I'm warming it or leaving it idleing for an extented period of time. Just for kicks though someone with pickup/ hr meter tell me if your any where near the 6200 hrs on my international with only 104,500 miles on it. most pickups/ work / family trucks have 100,000 miles at what 1800 to 2200 hrs?
by the way h20 what are your qualifications for ripping Lattitude Improvement about his wealth and owning twin diesel engines. More specifically what do you know about diesels. I am personally not in the tax bracket to own a single diesel(I'm getting closer to buying a diesel pickup truck) let alone twin diesels on a boat but he has a question about idleing his engines.
I'm not a diesel mechanic and don't claim to be but I've driven them for a while job related and feel the same rules apply to the water. They like to be run hard SOMETIMES but you have got to give any engine a break every once in a wihile.
L.I. I would simply say this, I think idleing one engine at a time would save very little fuel as diesels burn little fuel until they are pushed. Once they are pushed they will exceed any expectation to what they can do when compared to gas burners and still get better fuel economy while doing so. GPH burn at idle speed is minimal and should not equate to your float plan as it won't burn up a millionth of the 3rd fuel capacity you should save as a reserve. Idleing below 900 to 1100 rpm shouldn't be done on a diesel for extended periods of time because carbon buildup will happen and hurt future fuel economy and maximum hp.
Guys, just because we have a diesel engine doesn't mean we are all rich. I am looking for ways to reduce fuel consumption also. A typical offshore trolling trip is 266 gallons for me. The last trip, we decided toleave at midnight and travel out at 7 knots instead of full cruise. When it was all said and done, we went the exact same nautical miles and saved 36 gallons. So now, I have to determine if saving 36 gallons was worth a 19 hr trip vs a 13 hr trip?
Jags R 1 do you charter or are you private? I want to go tuna fishing and have a good friend in Jax that I'm trying to get me hooked up with a tuna trip. I posted earlier about tunas in N fla. and got some great responses. If you do trips I'd love to talk to you about a trip in late feb!
Amen ears and I guess just simply smoke up on that crack pipe there "watercop". I have driven an international for a while now and I leave it idleing most of the day that I'm not in it. I do bump up the rev limiter to a grand or so when I'm warming it or leaving it idleing for an extented period of time. Just for kicks though someone with pickup/ hr meter tell me if your any where near the 6200 hrs on my international with only 104,500 miles on it. most pickups/ work / family trucks have 100,000 miles at what 1800 to 2200 hrs?
by the way h20 what are your qualifications for ripping Lattitude Improvement about his wealth and owning twin diesel engines. More specifically what do you know about diesels. I am personally not in the tax bracket to own a single diesel(I'm getting closer to buying a diesel pickup truck) let alone twin diesels on a boat but he has a question about idleing his engines.
I'm not a diesel mechanic and don't claim to be but I've driven them for a while job related and feel the same rules apply to the water. They like to be run hard SOMETIMES but you have got to give any engine a break every once in a wihile.
L.I. I would simply say this, I think idleing one engine at a time would save very little fuel as diesels burn little fuel until they are pushed. Once they are pushed they will exceed any expectation to what they can do when compared to gas burners and still get better fuel economy while doing so. GPH burn at idle speed is minimal and should not equate to your float plan as it won't burn up a millionth of the 3rd fuel capacity you should save as a reserve. Idleing below 900 to 1100 rpm shouldn't be done on a diesel for extended periods of time because carbon buildup will happen and hurt future fuel economy and maximum hp.
Hey there, trucker!
Put your greasy John Deere hat and over-amplified CB microphone down for a minute, and enlighten us all as to the reason that you leave your rig running all day whether or not you are in it. What purpose does that serve? I understand the reasoning behind idling while you chaw down on the truckers special at the nearest greasy spoon, hey everybody feels the need to beat the system once in a while by fudging the books, but why do you do it?
Also, I don't doubt that you can't afford even a single diesel engine boat, since most truckers income is paid by the mile, and you only have 104K on your odometer for a few years work, you must not be making too much.
Sounds like you should be driving that rig instead of letting it just sit their idling all day...
Diesels idling on one engine to save fuel? 
