Engine Loading

[Nomad Willy]

Not a new topic I know. Steve DA stated a long time ago that a properly loaded engine should be run at 75% load 75% of the time. I've supported that standard many times and backed off a bit on several occasions. I assumed he'd get so much heat he'd back off on his hard line or at least confess that certain engine types need to comply and others don't. Many on this site, for example thought older engines were exempt. Well Steve DA has changed his tune a bit** ..* he actually RAISED the loading to 80%! That would mean a Ford Lehman 120 would need to burn well over 4gph to comply. Ive waited for a long time for Steve to moderate and say 60-65% or maybe even 50% on older engines. I'm probably or may be the closest to Steve's standards and I'm only at 55 to 60%. I still wonder why there is such a wide gap between what this "expert" is saying and what we all are doing with almost none of the terrible things happening that are supposed to come to pass. One could easily say Steve dosn't know what he is talking about or our engines don't know how to misbehave. Somehow I think it's more complicated than that. Consider this an update.

Eric Henning

 

[2bucks]

Steve is one guy shooting from the hip because he writes for one magazine. He has no real bonafides except that he has been working on boats 10 years fewer than I have, and a large number of others on this board. Steve writes glowing articles about whatever product helps finance the magazines thru advertising. His name on any product or article means to follow the money. The magazine he writes for is only about money, for ads, and for new items free to put on Growler. (a growler is a large piece of s..t left in the toilet for someone else to find)

Sorry to have to sugar coat my opinion of St. Steve. If you want my real opinion, just ask......

Ken

 

[Codger2]

I'm LMAO at 2bucks post........Don't be so shy...tell us what you really think!

 

[FF]

The problem is that diesels (at least in our sized boats) are all marinizations of something from the truck or construction industry.

Steve is right for a medium duty high speed diesel, as might be found in a working trawler or on a big genset.

Deadheaded once with a Cat engineer that claimed they were getting over 35,000 hrs from the Saudi gen sets.

80% rated load , 90% rated RPM, oil changes on the fly and 30 stories of hospital air cond to clean the intake air.

Most of our boats can be operated at minor loads as the engine came from a truck or bulldozer , not a 24/7 gen set.

BE HAPPY the Ford was from a tractor and not really heavier duty.

The good service rep of J Deere is because there are taken from the Jap construction industry , where light loading a good percentage of the time is normal.

When publishing in an adult area like Pro Boat Builder , Steves articles are the poorest in any issue.

FF

 

[markpierce]

How does one measure an engine's load?* Is it the ratio between actual*RPMs and maximum RPMs (which I doubt), or is it the percent of actual*fuel consumption rate*to maximum fuel consumption rate, or something else?

 

[jleonard]

If the boat is propped correctly you could base it on RPM and be very close to the loading curve for your engine.

But since it is really fuel that makes power basing it on fuel consumption would be more accurate.

What you really need to do is make sure the engine comes up to operating temperature if you are running lightly loaded. Monitoring EGT is an even better way because it's really cylinder temps you care about.

That's easy with a natural engine , a turbocharged engine with no aftercooler,* or a antifreeze cooled intercooler. Harder to do with a raw water aftercooler.

*

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*

 

[Delfin]

General rules usually apply to no one specifically. *My impression is that newer engines are far more sensitive to underloading because heat management is more critical to ensure emission comliance, although others can correct that impression if I am wrong. On my 3306, the oil is cooled so it is the temperature of the thermostat. *176 degrees whether she is running at 1150 rpm or 1700 rpm. *At 1150 rpm she is running at about 20% capacity. *I need 75% of rated hp to move at hull speed into a blow, and 20% to cruise long distances without pulling a fuel barge behind me. *For most displacement trawlers, this is reality (especially for those with 7.5 feet of draft like Delfin), which is why advice like running at 80% capacity all the time doesn't make a lot of pratical sense.

I blow it out every few hours by getting the EGT up from 500 degrees to 775 degrees. *Never the slightest smoke.

*

 

[Nomad Willy]

Engine loading is indeed closely related to power loading in a FD hull. If you want to run at hull speed it's best to have a slow SD hull** ...not a FD. A FD hull running at hull speed will benefit little or close to not at all from her stern wave while a FD hull running at about 85% of hull speed will be (to a degree) surfing on her own wave (like going downhill) and will be going 85% as fast as hull speed but burning half the fuel. My impression is that FD hulls are NOT designed to be run at hull speed. Hull speed should be their top speed or even less. As for needing more power in a blow I never increase engine speed ** ...I always decrease engine speed at least 300 rpm and always make acceptable headway. Regarding underloading the engine it seems there is rarely a problem so I'm not going to fight that one anymore but if one is going to repower why not power the boat for the speed it was designed for and run the engine at 75% load? Your chances of wearing the engine out at even higher loading are almost nonexistant. Furthermore the cost of your engine will be less to much less and your fuel burn will be less as well. Win win.

 

[Delfin]

nomadwilly wrote:
Engine loading is indeed closely related to power loading in a FD hull. If you want to run at hull speed it's best to have a slow SD hull** ...not a FD. A FD hull running at hull speed will benefit little or close to not at all from her stern wave while a FD hull running at about 85% of hull speed will be (to a degree) surfing on her own wave (like going downhill) and will be going 85% as fast as hull speed but burning half the fuel. My impression is that FD hulls are NOT designed to be run at hull speed. Hull speed should be their top speed or even less. As for needing more power in a blow I never increase engine speed ** ...I always decrease engine speed at least 300 rpm and always make acceptable headway. Regarding underloading the engine it seems there is rarely a problem so I'm not going to fight that one anymore but if one is going to repower why not power the boat for the speed it was designed for and run the engine at 75% load? Your chances of wearing the engine out at even higher loading are almost nonexistant. Furthermore the cost of your engine will be less to much less and your fuel burn will be less as well. Win win.

*It doesn't seem to work that way with all hulls. *I only know Delfin, but I'm not sure what the "speed she was designed for" would be. *Hull speed of 9.75 knots to get through Seymour Narrows when I eff up the timing? *I need about 200 hp and 12 gph. *8.5 knots for speedy cruising short distances? *I need 85 hp and 4 gph. *Lazy long distance ocean crossing at 7 knots? * I need 40 hp and 2.75 gph. *The reality is that with a full displacement hull that goes cruising, you need a fraction of the hp required to push the boat at hull speed when you are just putzing along. *So you either power the vessel so it won't hit hull speed, or buy an engine that is designed to operate efficiently for the long term at low power outputs. *The 35,000 hours FF mentioned the CAT guy told him was common is on an engine that might be turning at a constant rpm, but the load would be highly variable. *I heard the same longevity, in fact 50,000 hours, as not uncommon on CATs in service on the North Slope where they idled for 10 hours a day, then dug for 14 hours at highly variable loads. *

As with all things boating, I think this is an area of compromise.

 

[Nomad Willy]

Hi Carl,

You want me to "compromise"? Well** ...you do have a passagemaker and on long distance runs you have a need to do something normal boats don't have the need to do and that is to maximize your range. Normally I see no reason for you to go slower than 8 knots or faster than 8.5 knots. That's a very narrow speed range but FD boats only usually make sense in that narrow range. What does "eff up the timing" mean? Eff up same as screw up? Don't screw up. Be there at the right time and transit Seymour at slack. So "putz" around if you wish but it's my opinion your boat is over driven much over 8 knots. How much hp per ton do you have? 4 hp would be a good number but I suspect you have 5 to 7 or maybe 8. I think I'm a bit over powered at 5. I'm propped correctly and never run over 500 rpm down from max and almost always run 700 rpm down. So I could have 5 hp less power available and run 500 rpm down most all the time instead of 700. And I'd still have 2-300 rpm more to go. What I'm saying is that I think a true 100% full displacement boat like yours and mine is basically a one speed boat. Going any faster than 85% of hull speed just makes a huge wake and going any slower is**** ....well slower than the slow.

 

[Nomad Willy]

Jay,

Jay wrote "If the boat is propped correctly you could base it on RPM and be very close to the loading curve for your engine." Sounds like you're saying 75% of available power is at about 75% of rpm. Not even close I think. I'd guess 75% of power would be closer to 90% of rpm** ...but probably a bit less. 75% rpm should be about 50 to 55% power. I don't really know though so how-a-bout some other opinions** ...or even facts. Speaking of facts my boat runs at half it's max fuel burn at 2300 rpm (3000 rpm engine) and has a max burn of 2 gph (I think). That would compute nicely to 75% rpm and 50% power.

 

[Steve]

Does any one know where underloading would rank if the causes for marine diesel engine failure or serious damage were listed?
Steve W.

 

[jleonard]

nomadwilly wrote:
Jay,

Jay wrote "If the boat is propped correctly you could base it on RPM and be very close to the loading curve for your engine." Sounds like you're saying 75% of available power is at about 75% of rpm. Not even close I think. I'd guess 75% of power would be closer to 90% of rpm** ...but probably a bit less. 75% rpm should be about 50 to 55% power. I don't really know though so how-a-bout some other opinions** ...or even facts. Speaking of facts my boat runs at half it's max fuel burn at 2300 rpm (3000 rpm engine) and has a max burn of 2 gph (I think). That would compute nicely to 75% rpm and 50% power.

*I meant that if you are propped correctly you can use the engine hp curves and base it on RPM

*

*

 

[Nomad Willy]

Steve,

I only know of one case of engine destruction due to underloading and that was a stationary generator engine. The customer asked if running all winter in a nearly no-load state would damage the engine and the supplier said yes it probably would. He ran it and it required a rebuild in the spring. But that's the only case I know of.

Jay wrote:

" I meant that if you are propped correctly you can use the engine hp curves and base it on RPM" If it's the "engine hp curves" based on projected propeller loading then I think yes but if it's the max hp curves found on engine brochures then no. All the points on the brochure curves are 100% load at whatever rpm.

Mike,

I hav'nt see this issue on boatdiesel but I hav'nt spent much time there. Very good point about opinions and mine are as questionable as any but as I do keep uncovering stones I feel I'm getting closer to the truth. I like the objectivity in your post. Are your "subject matter experts" engineers?

 

[RED]

Eric

There is a table in the operating manual for my Cat 3208 that suggests variations in recommended loading depending on the type of craft. It gives a rating level C for yachts and specifies a time at full throttle of 11-50% with a rated RPM of 2600 and a suggested cruising throttle of 2300; this is actually 88% of full throttle rating. Cat claims this rating (and ratings for the other classes which I have not included) "obtains an acceptable match ... of total lifetime costs". So their recommendation is based on what I would call the integrated average lifetime power demand; ie "work" that the engine produces over time.

 

[sunchaser]

Tony Athens on boatdiesel.com has stated many times he has not*seen a marine engine die from underloading or operating at "low" RPMs.*Of the*many nonmarine failures I have seen, it seems to gravitate to the bolt ons failing. The myth about diesel engine underloading prevails it seems though, particularly in the age of texts, internet and Facebook.

 

[Nomad Willy]

Perhaps that's where all this engine loading stuff came from*** ....gensets. Some genset engine failed and stories went everywhere. Lots of other sources started sin'in the song like Northern Lights. A rep from NL said in an article (in PMM) about loading engines to "run'em like you hate'em". I've always heard stories by dealers and mechanics. Red, is that 11% to 50% of time at full throttle? And "88% of full throttle rating." ....meaning 88% of rated rpm? Only 300 rpm down from rated rpm seems like a very high load. That's about 400 down for me and I do run the Mitsu 500 down for long periods on occasion. This information you have Red should coming from engineers, not dealers and mechanics. The suggested cruising rpm of 2300 is a very long way from underloading. This means they recommend cruising at a high engine load. Do they recommend cruising at a low load? By recommending 2300 do you suppose that says high loading is good and implies low loading is less good or even bad? I suspect low loading is less good but not bad. The line in the sand is often drawn for maximum output but I don't ever recall hearing from a manufacturer that one must burn X gph for long engine life. Is there any manufacturer that specifies a minimum loading? If not that would at least imply that none is needed and therefore one can successfully run at any low loading desired. Or are there no recommendations because the manufacturers think no one would buy and install an engine bigger or more powerful than needed ....and the're behind the curve because only recently has anyone had the need to underload due to high fuel costs. However I have never heard that one must run an engine as slow as possible and at minimum loading to maximize engine life*** .....except here on the forum (no names). But the very fact that recommendations to run low and slow are spotty at best and largely unprofessional implies that there is at least no harm in running under low load. Tom seems to be right and the underloading issue seems to be just a myth. At any rate it dos'nt seem like anyone on TF is in danger of ruining their engine running slow. But I'm not convinced running one's engine hard is bad either. And Caterpillar seems to agree.

 

[Codger2]

nomadwilly wrote:
Perhaps that's where all this engine loading stuff came from*** ....gensets. .... Is there any manufacturer that specifies a minimum loading? ....However I have never heard that one must run an engine as slow as possible and at minimum loading to maximize engine life*** ..... At any rate it dos'nt seem like anyone on TF is in danger of ruining their engine running slow.

* * * ** My experience and other's I have known agree with the above statements.

******** Treat your engine well (maintenance) and use it to your liking. It will probably outlive

********* your boating life.

 

[RED]

Eric
Yes, the Cat info is from the technical ops manual. Cat, at least in the 3208 series "configured" the engines based on ratings - that is they started with the basic block and then added marinization options. (heat exchangers, coolers, etc). The class C rating was for "yachts, ferries with trips less than 1 hour, fish boats moving at high speeds out and back, and short trip coastal freighters".
They published a time at fulll throttle of 11-50%, which I think is their estimate of the time based on the useage of this class. The suggested reduced rpm for cruising speed is also their estimate of being at or near optimum efficiency. When we did sea trials, we came within 100 rpm of this number.
I wold guess that the recomendations are based on a combination of efficiency and projected MTBF, or failure rate.

Seahorse, I agree about engine life. I once asked a power plant engineer about the expected life of a power plant. His answer was "its like my grandfathers ax, it has had 6 handles and two heads, but its still my grandfathers ax".

 

[Delfin]

nomadwilly wrote:
Hi Carl,

You want me to "compromise"? Well** ...you do have a passagemaker and on long distance runs you have a need to do something normal boats don't have the need to do and that is to maximize your range. Normally I see no reason for you to go slower than 8 knots or faster than 8.5 knots. That's a very narrow speed range but FD boats only usually make sense in that narrow range. What does "eff up the timing" mean? Eff up same as screw up? Don't screw up. Be there at the right time and transit Seymour at slack. So "putz" around if you wish but it's my opinion your boat is over driven much over 8 knots. How much hp per ton do you have? 4 hp would be a good number but I suspect you have 5 to 7 or maybe 8. I think I'm a bit over powered at 5. I'm propped correctly and never run over 500 rpm down from max and almost always run 700 rpm down. So I could have 5 hp less power available and run 500 rpm down most all the time instead of 700. And I'd still have 2-300 rpm more to go. What I'm saying is that I think a true 100% full displacement boat like yours and mine is basically a one speed boat. Going any faster than 85% of hull speed just makes a huge wake and going any slower is**** ....well slower than the slow.

*She displaces about 65 tons and flat out the CAT delivers 270 hp with a C rating, or about 4 hp per ton. She needs about 1.5 hp per ton for normal cruising.*

Right now, we're coming back from Victoria, and I have some favorable current, but we are doing 8.7 knots at 1340 rpm, heavy load on the alternator using up a few hp and burning 4.1 gph per the FloScan. *Backed off to 1240, and we're doing 8.1 knots and burning 3.4 gph. *Since these settings only use between 60 and 80 hp, even though the hp per tonnage is rule of thumb, we probably are over powered. *A lot depends on the hull, I guess and how often you care about going hull speed.

Granted on your point that FD trawlers are predominantly one speed boats. *My point is that that hp to drive them at hull speed is so much more than what is required to drive them normally that a decision to power so that you are running near 75% power normally probably means you can't go hull speed, should you ever need to.


-- Edited by Delfin on Monday 27th of June 2011 01:31:16 PM

 

[Nomad Willy]

Carl,

OK good but why should I ever need to run at hull speed? And if I had such a need I would reflect on the fact that I had the wrong boat. I would be then better off w a SD boat. As you may recall I really want a 32 Nordic Tug but don't want to pay for the boat and every boat is to some degree a project boat and I don't want the hassle of that either. I'm really quite happy w Willy.

 

[Anthonyd]

I guess the best way to find out is if we compile the data over a long period of time and see what we get. I'm not that familiar with marinized engines in these boats, no disrespect intended, I have only worked on them in the construction or mining environment. Now I sail on cargo ships so the engines are either medium speed or slow speed. I do know of a 3306 in a hydraulic crane in northern Illinois that I have personally serviced over the years and the owner is meticulous about preventative maintenence. There are a whopping 62k hours on this engine. This engine drives the machine from site to site and operates the hydraulics for the crane and stabilizers. The operator/owner says he runs the engine at full throttle all the time the impliments are being used and won't idle for more than fifteen minutes, and has done so since he bought the crane new thirteen years ago. I also worked on a D-11 dozer for Cat in a mine in Arizona with 29k hours on it and the engine was a 3512. Same thing, run at high RPM as much as possible. As many have said, there must be something to the design specifications that allow for the lower RPM's and operating loads when the engine is intended to be marinized. Since my wife and I are looking for a Trawler I am really interested to see how all of this works out. Thanks to all for the great input and keep it coming. I have so much to learn about these boats and look forward to it.

 

[Delfin]

Anthonyd wrote:
I guess the best way to find out is if we compile the data over a long period of time and see what we get. I'm not that familiar with marinized engines in these boats, no disrespect intended, I have only worked on them in the construction or mining environment. Now I sail on cargo ships so the engines are either medium speed or slow speed. I do know of a 3306 in a hydraulic crane in northern Illinois that I have personally serviced over the years and the owner is meticulous about preventative maintenence. There are a whopping 62k hours on this engine. This engine drives the machine from site to site and operates the hydraulics for the crane and stabilizers. The operator/owner says he runs the engine at full throttle all the time the impliments are being used and won't idle for more than fifteen minutes, and has done so since he bought the crane new thirteen years ago. I also worked on a D-11 dozer for Cat in a mine in Arizona with 29k hours on it and the engine was a 3512. Same thing, run at high RPM as much as possible. As many have said, there must be something to the design specifications that allow for the lower RPM's and operating loads when the engine is intended to be marinized. Since my wife and I are looking for a Trawler I am really interested to see how all of this works out. Thanks to all for the great input and keep it coming. I have so much to learn about these boats and look forward to it.

*Don't know if it's true, but an engineer here in Seattle I spoke with said he worked on the original design team for the 3306 when he joined CAT out of college.* One of the design briefs was to build an engine that could operate in the extreme cold of the North Slope, which meant long periods of idling followed by long periods out maximum output running dozers, excavators, etc.* Maybe that is why they work out ok for marine engines.* He also said he saw a lot with 50,000 hours on them.

I don't think that modern engines are built to do this.*