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Is full throttle harmful?

Discussion in 'Engines' started by T.K., Apr 29, 2007.

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  1. goplay

    goplay Senior Member

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    There definitely is more wear at higher RPM: higher pressures, higher vibratoins and higher temperatures will cause metals, oils and fuel to behave differently than at lower temps.

    I used to race cars and the engines would be rebuilt every 50 hours. The pros would rebuild every 20 hours. The Porsche Cup Car race engines are more-or-less identical to the street GT3 engines. I probably have over 1000 hours on my street GT3 and while I haven't dyno'd it, subjectively, it is not in any need for a re-build. The difference of course is that a race car is run very hard: it is close to redline or it is braking.

    So you can run at full throttle for extended periods, it just means your engine wears out sooner.
  2. Ben

    Ben Senior Member

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    My engine knowledge centers more around cars than marine, which also means more petrol than diesel, but I think goplay's link with racing cars and road use is the best yet.

    Using and unmodified family car as a racing car will destroy it. It may not go "bang" but at the end of just one hard days racing there's a very good chance you will have broken something and may need a tray truck to get home. But if treated correctly that same underengineered car should give years of faithful service, even allowing for a few WOT (Wide Open Throttle) traffic light drags.

    The point being that whenever you use an engine it wears and the further the engine goes outside it's comfort zone, the faster it wears. I think engine wear outside the comfort zone is also likely to be more exponential than linear.
    Ie. Running an engine at 100% instead of a comfortable 90% won't just decrease your engine life by 10%.
    This also matches with the fuel consumption and engine life advice, as running at 100% doesn't just increase your fuel usage by 10% either.

    If you want to run your engine constantly at WOT you should buy an engine that is rated to 100% duty cycle. After looking on the Cat site I'd guess that and engine that is rated for 1000hp in high speed domestic use would be rated closer to 750hp if it was for "Unrestricted Continuous" use.

    I can't tell you how long is to long when it comes to WOT use, it's really a game of percentages, the more you do it, the faster it wears out. Just like your car.

    As for the engines having some sort of safety margin, I doubt that an engine rated for 1000hp gets restricted to 900hp at manufacture to make sure the end user doesn't thrash it.

    And as goplay says, electronics won't stop you destroying or wearing out your engine faster than normal, they just ensure you get smoother running and better fuel economy while you do.

    They help, but in the end your the boss.
  3. Many yacht buyers have an engine surveyor investigate the condition of the engines in a yacht they are purchasing. With the new computer readouts of engine hours, fuel used, percent of time at full throttle, and much more information, a surveyor may question an engine that has a high amount of hours at full throttle.

    Will this affect the sale of the yacht? Will the buyer ask for a price reduction if he has concern for the longevity of the engines? Will the surveyor question an engine with high full throttle usage? These questions can not be answered in advance, but it is something a yacht owner should know about before a survey happens.

    If the extra fuel cost is not a concern, maybe the cost of reduced life expectancy may not be a concern either.

    Tucker Fallon Yacht Broker
  4. CaptPKilbride

    CaptPKilbride Senior Member

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    How do you keep track of engine load? Will the engine electronics do this? I ask because i have zero experience with electronic engines.

    I have seen a performance curve for a new DDC/MTU engine, the 16V2000 M93L. It has a standard load profile that states I can run at:
    100% load 10% of the time
    70% load 70% of the time
    <10% load 20% of the time.

    When underway will I be able to see the load on the engine in addition to all my other monitoring parameters like RPM, temperatures and pressures?

    Attached Files:

  5. Indigo2

    Indigo2 New Member

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    On the Cat C30 you can get that data. Having the SIMON monitoring system you get even more, such as the gallons of water for the Genset raw water. Depends on how it is set up. The MTU electronics give good data as well. Much more than I was used to at the time. I created a worksheet so I knew the ranges I wanted to work within for each parameter and know what normal was.
    I use the 70 % load factor depending on the rpms and gph. If that changes during normal operations start looking. If you have a long trip and want to conserve fuel by using lower rpms, the last 15 min or so before entering port I increase the rpms to clear out the carbon that may have accumulated. That low load running will also decrease the time between overhauls. The MAN engine that I am familar with used one side of the engine for lower rpms and as you increased then the other side would be in use as well. That meant that with low rpms only one side of the engine would wear. In the end you would lose the high end of the rpms slowly and it is rebuild time. At least that is what the mechanics told me. :)
  6. CaptPKilbride

    CaptPKilbride Senior Member

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    Great info Indigo, thanks!

    I am wondering if anyone else has any experience with the new MTU common rail engines? And what form the engine history reporting takes?

    As a for instance, after a year of running the boat at varying throttle settings, can I do a summary report that shows average load over time? So I can know if I am close to exceeding the parameters of operation set by the manufacturer and in doing so may void the waranty?
  7. CODOG

    CODOG Senior Member

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    A point of interest when talking of power ratings, duty cycles and accountability (customer wants a warranty, engine manufacturer wants to limit its liability).....
    Its not unusual for engine manufacturers to hold something back in reserve when commissioning / accepting / offering warranties on new installations. This can be done by demanding that the engines see no more than (say) 96% load on engine trials, or that the boat is fully loaded during same trials, or in some cases both.
    Why ? Its an accepted fact that many pleasure-boat owners think nothing of running their boats at max rpm at maximum boat load (full of fuel / gear / people etc), add to this assumed future bottom fouling, additional gear on board over time etc etc and you can begin to see how the engine manufacturers (or at least the commissioning agents) want to keep a power reserve to cater for this assumed useage.
    Lets assume that the boat has been set up for max speed / power / rpm at say, half-load, and that the LCG / propellers / gear-box ratio have been optimised for this design point. Lets also assume the owner has been advised and understands that full engine rpm at heavier boat loads would not achieve maximum performance...its extremely hard to convince the commissioning agent that the boat will actually be run like this and they set the engines up with a load margin in hand...in some cases actually asking that the props are tweaked to achieve their preferred figures.
    The bottom line in many instances is that you pay for engines rated at 'X' power at 'Y' rpm, but to get your warranty, you may never see more than (?) 95% of this, and even then at a boat load heavier than optimum. The boat never sees its potential max speed as full power is only available at maximum boat load (hence compromised gb ratio, prop design and LCG) and even then, theres another few percent of power you will never see unless weed is allowed to foul the bottom:)
    My point is that rated power and duty cycles are only part of the story...
  8. CaptPKilbride

    CaptPKilbride Senior Member

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    Good points, CODOG.

    After investigating waterjet options, I came across this page on the internet that gives the subject a good treatment as well:
    UltraDynamics Waterjets

    It is a tightrope walk between the customer wanting to purchase a product that will deliver upon it's advertised claims, and the manufacturer who must protect his bottom line in order to stay in business and support his product.

    There is no doubt there is competition among manufacturers to produce a more powerful and lighter engine, but they have to balance durability as well.

    And, you have the consumer, and I am referring mostly to high speed yachts here, that is shelling out a lot of money and is going to be pissed if he is sold a product that cannot do what was promised.

    After all, in the case of my question of doing an annual summary of load ranges and percentages, I don't want to have to tell my boss that for the next 25 hours we cannot exceed 10 knots in a yacht that was spec'd to do 40 because there is the chance of voiding the warranty.
  9. brianwill

    brianwill New Member

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    If you consistently run an engine above 75 - 80% of it's maximum rpm rating you will shorten it's life.
  10. Portline1

    Portline1 New Member

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    have to put my 2 cents in

    Common sense dictated that you wouldnt....why burn the extra fuel for the modest increase in speed? been running boats a long time, and depending on the engine mfg they are different, but a good rule of thumb is cruising rpm is at 80% load, not engine speed. There is a sweet spot where you are getting the best speed at the best load at the best fuel consumption...every engine is different. You can safely run the engines at 100% for 10% of the time....but watch the temperatures......
  11. boatman82

    boatman82 New Member

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    After 30 years in the sea with mechanical and later on with full electronic diesel engines the best for any diesel engine is to go on 80% load and have fun and no problems with your engines for many,many years.
  12. John DeCaro

    John DeCaro New Member

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    What is the engine rated at?

    Hi all,
    From what I can see your have engines that are 3 rated, see below.
    "For commercial vessels or craft with high demands on speed and acceleration, planing or semi-planing hulls in cyclical operation. Typical boats: Fast patrol, rescue, police, light fishing, fast passenger and taxi boats etc. Full power could be utilized maximum 2 h per 12 h operation period. Between full load periods, engine speed should be reduced at least 10 % from the obtained full load engine speed."

    I have to say this was not easy to find on the volvo site. what it means is you can run full out for 2 hours and then run at 10% below for 10 hours and then another 2 full out. It is my understanding that you can run for 2 hours and then dock, if the engine cools down completly you should be able to run again for 2 hours,

    If you are running like this you really need to keep track of fuel burn as your service times will come up much faster then if you just use running hours.
  13. John DeCaro

    John DeCaro New Member

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    Engine ratings

    You really need to know what your engine is rated at.
    A "A" rated or "1"rated depending on the system is a continues duty engine.
    It can be run 24/7 at full RPM, it will not be the must economic speed but it will not harm the engines (in fact most are very happy there). As a rule most engines operate at their best economic RPM at 10 to 20% below max RPM. Some engines have a very sharp fuel burn and HP output at the top range of RPM, Detroit’s and MTU as an example, so 20%, other have a very linear curve like Cats, 10%.
    It is interesting that a lot of A rated engines do not like to run for long periods of time at 20% RPM because they do not reach optimum operating temp at those speeds.
  14. Kenny's Toy

    Kenny's Toy New Member

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    I wouldn't do it, just run them at 2100 to 2200 and they will thank you...
    too many people run these new engines so hard, as if they where race engines, the truth is they are more fragile than the older mechanical engines that cummins, detroit, or cat build..
    no wonder so many yacht owners have lawsuits against cat, man, cummins to name a few, little do they know that sometimes its there own fault :rolleyes:
  15. John DeCaro

    John DeCaro New Member

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    Hi Kenny,
    I agree with you, if you have the choice.
    But he does not, the owner wants to run the engines full out and he needs to know how long he can do so and not harm them (be within the engine rating) If he lies to him and the owner finds out then he is going to look very bad.

    At least this way he can run for two hours or one hour and 45m and then tell the owner that he will be outside the rating if they keep it up and have the force of the tec info behind him.
    If he just says no, I would expect he would be looking for a new job and someone who does not know about the rating will be running the boat (at least as long as the engines stay together).

    Per the other posts he can also explain to him that he is going to spend a lot more money and not just on fuel by running full out.
    Maybe he will just save it for when the girls are on the boat?
  16. Capt J

    Capt J Senior Member

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    Yes, MTU can plug in their laptop to your engines and a graph will pop up with percentage of use at each load factor or rpm, same as CAT and MAN. They will also void a warranty in a heartbeat if it has been run WOT too much.

    I would never run an engine at full throttle for any period of time, as exhaust temp is very high, boost pressure is very high, as well as wear and tear. Cat and MAN recommend running their engines at 80% load factor wherever that may be in rpm's. It varies from boat to boat and propeller design. What are you gaining by running full throttle, a few knots and a heck of a lot more fuel consumption. Also most engine manufacturers are changing to total fuel used as a rebuild factor instead of engine hours. I still prefer to run 400 rpm's off of top in most vessels, as it is slightly lower in rpm's over 80% load and a lot more efficient with less coolant temperature and exhaust temperature.

    Engine manufacturers are not de-rating their engines 10% as a safety margin. They are trying to come up with the most HP to engine weight/size in order to gain more marketshare. Electronics has enabled them to get a lot more liberal with engine HP, specifically turbo boost in order to make HP in a safe package.
  17. Capt J

    Capt J Senior Member

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    I would be looking for a new job regardless. Owner's like this always push the envelope, running too fast in rough seas, things breaking because of it, engine issues, etc and you end up looking bad and loosing your job because of it anyways with a bad reputation to boot. Try explaining to the owner that he can't use his boat for 3 months because one of the engines grenaded all over the engine room and has to be rebuilt, and chances are he will blame the captain anyways. Especially when Volvo (who happens to be the strictest in regards to covering warranty claims in comparison to CAT) tells him that they are not going to cover the rebuild under warranty. I have seen MTU try to deny a warranty claim on a 16v2000 in the boat next to us (after the boat I worked on grenaded one at 300hrs due to piston rings installed upside down), because the engine oil was a 1/2" over full on the dipstick.


    Your job as Captain is to ensure the safety of the vessel, crew, and passangers. Insisting on running full throttle to gain very little in speed basically describes an owner that doesn't care about the safety of the vessel. It just means that as Captain, you are going to have to fix a myriad of things that shouldn't have broken for an owner that can't take no for an answer.
  18. K1W1

    K1W1 Senior Member

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    Hi,

    CaptJ you might be interested to know that CAT have a variety of ratings for their engines some can do the rated power 24/7 and others can only do it 2 hrs in 12.

    I am involved an an application where we have a pair of A rated 3516 Series 2's, our performance contract and cruising speed were given for 90% MCR Operation. The Fuel Consumption jumps through the roof in the last 10% and breaks the 16,000 lt a day threshold without the generator which drinks a further 1500 Lt at normal cruising loads.