Click for Cheoy Lee Click for Walker Click for CL Yachts Click for JetForums Click for Cross

Is full throttle harmful?

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

You need to be registered and signed in to view this content.
  1. T.K.

    T.K. Senior Member

    Joined:
    Jan 31, 2007
    Messages:
    1,020
    Location:
    Cairo - Egypt
    I have a Fairline Phantom 48. Will sailing continiously for about 2 hours at full throttle, 32 knots @ 2500rpm harm the engines or is it acceptable? The engines are Volvo Penta D9 575. I understand that fuel consumption will be very high, however will there be any adverse effects on the engines or can they safely sustain this rpm?
  2. AMG

    AMG YF Moderator

    Joined:
    Jul 26, 2004
    Messages:
    5,302
    Location:
    Sweden
  3. T.K.

    T.K. Senior Member

    Joined:
    Jan 31, 2007
    Messages:
    1,020
    Location:
    Cairo - Egypt
  4. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    Isnt 10% below the maximum RPM the "cruising" speed?

    afaik (and the volvo penta manual seems to agree... so does the MAN ones i recall looking at) the "cruising" speed is merely for fuel economy.

    The efficiency of the engine is also usually higher at its optimal RPM (which may be the "cruise" RPM and not the top).

    The VP manual clearly states that the engine shouldnt be run at top RPM due to fuel economy... I have been on boats on full throttle for more than 2 hours... although most crew prefer to ease off of 100% throttle, many owners on go-fast boats like to be at 100% or near that when they're on board...

    I'm pretty sure you are fine... if you have doubts ask your volvo people, but i highly doubt it that you could cause a lot of damage to new, electronic engines, merely cause you run them at top speed... thats preposterous... (d***, my MAN diesels often complain when nothing is wrong... if anything starts going wrong these engines are programmed to detect it and shut themselves down, or throttle back)... I think you're safe throttling up all the way! (I dont know however, if there are any recomendations about breaking the engine in or something equivalent...)

    EDIT: page 44 of the manual says it all...
  5. AMG

    AMG YF Moderator

    Joined:
    Jul 26, 2004
    Messages:
    5,302
    Location:
    Sweden
    Thanks RoyN, very informative. I will submit it to my friends at Volvo Penta...
  6. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    Don't quote me, quote themselves :p :D

    But yeah, on Pershings we often cruise for medium lengths of time at full throttle... (when the sea is absolutely calm, that is... otherwise its just too lousy in terms of comfort...)

    *above comments go for 43 and 52 Pershings... i have not experience or information if the above holds true with other sizes*
  7. Norseman

    Norseman Senior Member

    Joined:
    Feb 24, 2005
    Messages:
    2,586
    Location:
    Ft. Lauderdale
    Some diesel gurus recommend 70% of max continous for best efficiency. (Non-turbo)

    I ran a boat with two 1300 HP MAN engines for a while:
    The owner wanted full throttle most of the time.

    The engines were happy to do that, but with a modern electronic furel control system that monitored all parameters, including exhaust gas temps, fuel flow, cooling temps, etc, etc.

    Running full blast with an older diesel, I would be careful.
  8. T.K.

    T.K. Senior Member

    Joined:
    Jan 31, 2007
    Messages:
    1,020
    Location:
    Cairo - Egypt
    Thanks Roy.

    The manual says "Avoid operation at full throttle for best fuel economy".

    It does not mention anything regarding additional mechanical stress or engine damage nor affecting engine longevity due to the operation at full throttle, i.e. about 2500 rpm. So I take it if fuel efficiency is not an issue going full throttle is ok?
  9. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    I'd assume so... As the previous poster seems to agree, this shouldnt really be harmful to electronic engines... they should protect against this sort of thing.

    About the non-electronic engines, I remember that they felt much less at ease at full throttle then the electronic ones. The newer ones seem to be comfortable at all power spectrums. In fact, our captain used to say that the engine was running "steel-to-steel" when he meant that they were at 100%... ever since we changed to boats with ECC engines, I havent heard him use the expression ;)
  10. Loren Schweizer

    Loren Schweizer YF Associate Writer

    Joined:
    Apr 20, 2004
    Messages:
    1,358
    Location:
    Coral Gables/Ft. Laud., FL
    Rant Off

    I have a difficult time wrapping my mind around the concept that just because an engine is 'electronic' that one can run the engines full throttle for long periods of time.
    Forgetting for a moment the stresses involved on the mechanical parts, these engines are not designed to perform like this.
    There are various ratings for diesel engines, some of which do allow for full-time full throttle operation: these are usually known as 'continuous duty' engines and are typically a lower horsepower application (for trawlers, say) as opposed to fast, planing boat engines.
    Caterpillar, for example, offers up a 'D' (intermittent duty) engine allowing for operating at rated load/speed 16% of the time and the 'E' (high performance) engines are allowed to run at WOT only 8% of the time-- that's a half hour out of every six.
    Volvo Penta may differ, but probably not too much.

    Propeller-load fuel curves supplied by the manufacturers generally trend up more sharply at the higher rpm ranges up to full-load: lots more fuel for incremental rpm rise.
    The engine company engineers will tell you that it isn't the number of hours that dictate an engine's life; it's the amount of fuel that "goes down the holes".

    Race car engines are one thing, but every marine diesel engine out there was manufacturered to specified tolerances (a little tight here, a little loose there) and some of those were built by human beings on a Monday or a Friday.:eek:

    Rant On

    Just like Spouse Abuse and Animal Abuse, there ought to be a law against Machinery Abuse.
  11. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    Loren, you are absolutely correct... Nonetheless, electronic engines have sensors and I have personally experienced them throttle down, alarm or even shut-off on their own when temperatures went high, pressures out of the proper range, etc... My comment about it being fine with electronic engines was merely because the engine seems to be more cushioned in those cases... On a mechanical engine there is no smart sensor or computer that will throttle it down if it is working so hard that damage could be done. Electronic ones tend to do these (I'd say they tend to alarm all-too-often, but thats just my experience)...

    I also have an unfounded feeling that electronic engines are generally slightly undertuned in comparison with their mechanical counterparts. If not undertuned, they are at least "less prone to be pushed to the mechanical limit"... All of this is good things (unless you start having glitches that factory technicians dont know how to debug)...

    And yes, I have heard on occasion that what determines an engines state is the amount of fuel its gulped, and not the number of hours - it is an exact paralel to engine mileage on a car, nonetheless due to convenience, we just use engine hours and we assume that will be an OK average (as a matter of fact it probably is in most similar boats - i.e. pershing boats will be pushed more to the limit on average than long range cruisers, on average)... Anyways, running at full throttle will put more wear and tear on the engine, but it will be related to the amount of fuel that is going through it (you are making it work more per hour at 2500RPM then at 1000RPM), with that said, we must keep things into perspective: your brand new volvo engines are not made to go through 3 or 4 tankfulls in a lifetime, so in the end, there is really no considerable and palpable harm in going full throttle when you want to get to a beach quicker, or outrun a small patch of weather or something...
  12. Jage

    Jage New Member

    Joined:
    Jul 1, 2006
    Messages:
    28
    Location:
    Tampa Bay
    Roy, that is a very interesting point about engine usage, more specifically the "wear and tear" among the different style of yachts. Assuming planing yacht engines are pushed more than other style yachts.... what in hours of use would be considered high relatively to a prospective used yacht buyer? Thanks

    Jage
  13. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    I honestly don't have the technical background to answer definitively... I've seen engines with a few houndred hours run badly, and I've seen engines with a thousand hours running very well. I suppose it depends on usage pattern and maintenance...

    With that said, if you are considering buying a boat I'd look for a few things:
    - warranty from the engine mfgr? still in effect?
    - get a good mechanic or authorized shop to look at it
    - watch how it runs, does it smoke a lot? does it leak oil? etc...

    I'm by no measure an expert on engines, but I've owned a few boats and I've been around many docks and boats, these are things that are tattle tale signs of problems, but it isnt really easy to spot a good engine from a bad one, based on number of hours and years... (As pointed earlier by another user, there is also the question of different engine models being appropriate for different duty cycles. I assume continuous cycle engines might outlast the other kinds in the longrun? maybe not, but i'd suspect that...)
  14. Jage

    Jage New Member

    Joined:
    Jul 1, 2006
    Messages:
    28
    Location:
    Tampa Bay
    Thanks and I was just asking generally. Certainly a mechanical survey is a "must."
  15. goplay

    goplay Senior Member

    Joined:
    Mar 16, 2006
    Messages:
    169
    Location:
    Sausalito, CA
    High performance diesels that one would find in pleasure boats are not intended to run at full throttle for extended periods. Check out the web pages of the engine manufacturers. There is a big difference between the duty cycle of pleasure yachts and working boats. Electronics has absolutely nothing to do about it.

    Second, engine rebuilds have everything to do about the gallons of fuel burned and not about hours operated. The hours operated are simply a rule of thumb based on average use for the typical consumer. Burn more fuel faster, rebuild your engine sooner.
  16. T.K.

    T.K. Senior Member

    Joined:
    Jan 31, 2007
    Messages:
    1,020
    Location:
    Cairo - Egypt
    In your opinion which length of period is considered safe to run a pleasure boat at full throttle?
  17. TSI AV

    TSI AV Senior Member

    Joined:
    Mar 21, 2006
    Messages:
    104
    Location:
    Estonia
    Hi,

    Straight question - straight answer...

    100 % load WILL harm Your engines.

    But...

    What is meant by "100 %" ? A lever on the bridge ?
    If yes, then it's only a lever at mark of 100 %. The engine itself will be appx 85-90 %. Because it's preadjusted like this. Every engine's manufacturer provides engine with controlled fuel rack limiter(s), but most important - with mechanical fuel limiter (normally it is a bolt with contra-nut), which is sealed. This is a limit.
    Well, I would advise You not to touch it...

    Guys, LEVER on the bridge never shows "load in fact" !
    Engine's load / performance is shown by :

    1. Fuel rack index
    2. Pz
    3. Exhaust temperature.
    4. Turbo rpm
    5. Charge air pressure.

    Please note, that engine's rpm is NOT a load indication !
    However, rpms have to be limited as well.

    A nice story, regarding rpm...

    Once upon a time,
    A governor was sent for overhauling. After completion it was nicely installed again. For some reasons, linkage between governor and engine's fuel rack was wrongly assembled.

    After start-up, engine began to rise rpm.
    But, when indicator showed 2x of nominal (!!!), engineers attempted to stop the engine by pushing fuel rack to "0" position.
    But the engine never stopped........., even when fuel line was cut.......

    Well, 3 connecting rods were out from crankcase, 5 cylinder heads flew away,
    all bearings were damaged and block was dented.
    Luckly, no injuries...

    The end.
    /////

    The moral: Please follow engine's manual ! Do not adjust mechanical limiters !

    Please bear in mind, that no engine's manufacturer will advise You to run 100 % (because of the warranty).
    At the same time, they will not tell straighlty, that You can't. (because this will mean their engine's low performance).


    Regards,

    Andrei
  18. T.K.

    T.K. Senior Member

    Joined:
    Jan 31, 2007
    Messages:
    1,020
    Location:
    Cairo - Egypt
    Convincing answer Andrei. Already full throttle on the levers is at least 10% below actual engine limit.
  19. goplay

    goplay Senior Member

    Joined:
    Mar 16, 2006
    Messages:
    169
    Location:
    Sausalito, CA
    It is true the throttle position does not necessarily corresspond to engine load. The engine electronics gives a better indicator of the engine load factor. Some may argue that there is a cushion built-in to that number even, probably is.

    The short answer is that you won't "damage" your engine at full throttle for extended periods, you dramatically shorten time between rebuilds. The engine won't blow-up, rather, it will start losing power.



  20. RVN-BR

    RVN-BR Senior Member

    Joined:
    Mar 28, 2007
    Messages:
    258
    Location:
    South Florida & Mediterranean
    Right, but reducing rebuild times is based on the amount of fuel being burnt, not because it is at 100%, right?

    So hypothetically speaking:

    Running the engine at 25% throttle will make you need a rebuild at a larger interval than at 50%, and this relationship is somewhat correlated to 50% and 100% instead of the above numbers... Becuase the fuel consumption goes up dramatically and exponentially when you go to higher RPMs, the rebuild time isnt linear when comparing it to throttle RPMs...

    Its complex, and running the engine at faster speeds will cause more wear, but it wont be abnormal wear, it should be the same wear as at slower RPMs, however it will happen quicker because of the obvious amount of fuel being bigger...

    It's like a car being driven at 10kmh, it will reach 100km odometer after 10 hours... if you drive it at 100kmh, it will reach the same point at 1 hour... will require service sooner (of course my example is stupid cause it doesnt account for gears and etc, but its somewhat similar parallel)...

    Is what I'm saying correct, or is there abnormal wear at higher RPMs??? (Of course, I'm not even considering changing anything such as governors or limits - mechanical or electronic)