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  1. #31
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    Jan 2003
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    Default

    Yes Fred but each of your engines must have the power of well.............at least two raindeer, and they never have to gallop :~)

  2. #32
    Join Date
    Aug 2004
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    880

    Smile

    "Is there anyone who has owned the same boat for say 3 years, single or twin, who has not had to attend to turbo problems? ................rant over"

    Yep me, I have the mid placed turbos' on my mechanical CAT3126's and I've not had any bother from them

  3. #33
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    Jan 2003
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    Hi Chriskaye thanks for that. The more I research this the more I am convinced it is due to misuse by previous skippers, i.e. cold engine straight to full throttle , and hot engine straight to switch off, plus perhaps lack of oil changes which are crucial

  4. #34
    Join Date
    Aug 2004
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    880

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    Hi SunCoast
    I am 30mins away from the solent so can't go cold to full throttle

    Also regular oily changes, I dont bother with the CAT oil samples and with these CAT 3126 mechanicals (425hp) engines you must only use CAT SEO (I think they call it), basically it's monograde SAE30. DO NOT use multigrade oil...................I use shell rimula X30 and its cheap too and goes in the gearbox to

    Boatdiesel is a brill source of info as is Clubsearay (diseasel section)

  5. #35
    davidjackson's Avatar
    davidjackson is offline Registered User
    Location : Home: North West, Boat: Anglesey
    Join Date
    Jun 2007
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    Hi guys, my boat has a big stick in the middle so I hope you'll allow me to contribute on this foreign forum!

    I worked for the world's largest turbo manufacturers for 20 years and I'm an engineer so I think I'm qualified to comment.

    Modern turbochargers are an integral part of the engine and have the same life requirements. They do not "kick-in". There is a fundamental mis-match between a reciprocating engine and a high speed rotating device. Over the years, advances in compressor and turbine stage design plus other technologies, such as wastegating and variable geometry, has made "lagg" almost imperceptable.

    Superchargers, regardless of type (the humble roots or one with internal compression) are generally capable of increasing air density sooner (on the torque curve) than a turbo. That's their one advantage. Most everything else about them is a disadvantage. Most significantly, they have very high parasitic losses (there are inefficient). Read "fuel consumption".

    Most marine engines are derivatives of the basic road going version. This is mostly an economies of scale thing. They'll have a number of power ratings from "work boat" through to "leisure". A rule of thumb higher power equals lower life and hence a workboat will be rated, say, 200 bhp and the leisure version will be, say, 300 bhp.

    Engine output is generally limited by air density (not fuel - it's easy to supply more fuel). Naturally aspirated diesels near enough do not exist anymore. Turbocharging increases air supply. Compressed air is hot. Intercoolers then cool the hot air and from school boy physics you'll recall that cooler air is more dense, hence more oxygen for combustion.

    Turbos are very reliable! All they ask is decent, well filtered oil and a good filter to the air inlet. Modern engines are designed to get oil to the turbo bearing as quickly as possible and the base engine will have been tested for oil supply time at something like -30 deg C.

    It's true that once the engine stops, the oil circulation will stop and the turbo may still be spinning. Again, it should be designed to tolerate this but common sense should prevail when stopping an engine (let it reach idle first).

    Hot shut down is about as bad a thing that you can do to a turbo. Not only will it be starved of oil, as above, but any residual oil may break-down by the heat and form carbon. Carbon deposits will kill the bearing in no time at all.

    Many turbos have water cooled bearing housings for just this reason.

    Water cooled turbine housings are used to meet "external touch temperature" requirements. It's contradictory to cool the turbine because it takes its power from M.Cp.delta T (basic law of thermodynamics). By design, it's nearly impossible to stop thermal cracks appearing over time. The exhaust gas may be 800 deg C and the outside touch temp may be little more than 50 deg C. Nothing to do with KKK using poor quality iron (although it did make me smile).

    A marine engine is likely to run at sea level only. A truck engine may have to pass over a mountain range. As the engine gains altitude, the air density will be lower and hence the turbo will try to work harder to generate the same power. To an extent, turbos give a degree of altitude compensation.

    The number of times you hit the throttle, how much load you're carrying and how long you run at said speed all gets computed to form what's called a Duty Cycle. Life is always based upon the duty cycle.

    Turbos can fail from low cycle fatigue (compressor stage) or high cycle fatigue (generally turbine end) but this is well outside the scope of day to day use. Fatigue will have been designed out based upon the duty cycle. That said, a blocked air inlet has the same effect as increasing altitude so it's always worth a check.

    Foreign object damage, after lubrication, is usually the reason for failure. A bit of rag through the compressor will kill it in seconds, as would a broken inlet filter. Turbine foreign object damage by definition must have gone through the engine first.

    If anyone else has a bad word to say about turbos I'll make you sail at 5 kts while standing 20 degrees away from verticle

  6. #36
    Andrew_Fanner is offline Registered User
    Location : ked into poverty by children
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    Mar 2002
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    8,517

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    >>>
    If anyone else has a bad word to say about turbos I'll make you sail at 5 kts while standing 20 degrees away from verticle
    >>>

    Turbos are ****, gissa ride Mister:-)

    I assume the turbo units (Holset ISTR) on my 6354s were intended to be quite tolerant of foriegn body ingestions as the stock "filter" would only exclude anything more than 1mm or so across, but anything smaller would get eaten. AFAIK both turbos work, insofaras I use them on the non-tidal river.
    Two beers please, my friend is paying.

  7. #37
    Join Date
    Dec 2001
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    1,967

    Default

    yep, 10 years with my old Birchwood with Volvo's no probs! having said that I might be tempting fate!!! why do you do this sort of thing? oh god all I will be thinking of over Christmas is how much its going to cost me to replace my turbo's!!!

    Barry

  8. #38
    Join Date
    Feb 2008
    Posts
    2,182

    Default Turbos

    David congratulations,

    Data based comment from somebody with an engineering background at last!

    Until I jacked in my practice insurance 90% of vessels surveyed failed the most basic application guidelines on fuel systems, exhaust systems and electrical systems, pretty much in that order.

    It appears that yard monkeys at the majority of builders do not follow the basics of RTFM, read the f#%&"*g manual.

    Many technicians in the field seem to be blind to putting gauges on actually obtain an insight into the engines operating environment, merely diving into engines and changing components at will.

    Dirty and or restrictive air filters, inadequate engine room ventilation, exhaust systems with well over 3 inches of Hg back pressure, ridiculous EGT’s, yep they are all out there. The term Vetus is not permitted in my company. I have lost count of the times that turbochargers have been needlessly replaced or fuel pumps recalibrated because vessel was marginally propped and had weed growth!

    Turbo charging is a robust technology; however all of the preceding conditions are potential killers. Add the occasional engine manufacturer who employs a team of ‘couch engineers’ on a development project who have never seen the inside of a boat and you are in deep trouble. Examples of couch engineering are the poorly designed low mid mount exhaust manifold on CAT 3126 as well as the crazy Mercruiser/VM exhaust riser, both designs are marginal at best and will allow small but unacceptable quantities of sea water back into the turbine housing. I have the material spec of the KKK housing, this would not meet Holset specifications however I concede that one of their turbos would survive little better in the given environment. Simple fact is that the iron housing disintegrates.

    Whilst I am in mid rant let me change gear on you and touch on electronics and fuel systems.

    Whilst I suffer from green engine blindness I see a barrage of negativity regarding Volvo D4/6 electronics. You can be sure of one thing the vast majority of so called electronic horror stories can be laid at the door of numpties who installed the motors and systems, they did not RTFM!

    About two months ago a long running saga came to a head, NOT Volvo engines I might add. Owner complained from new that throttle response on his new boat was poor, so much so that after three years he wanted to sell the vessel. Perspective purchaser went out on sea trials and noticed that one engine had higher boost pressure than the other; he was concerned that one engine may have a stuck waste gate (here we go lets blame the turbo again). I was asked to investigate, as this was a deal breaker.

    Problem was complex but simply solved, manual gauges confirmed engines in spec. Why was one electronic gauge telling lies? Appeared that after engine shut down the one gauge was retaining .5 bar of residual boost pressure after key off, then adding it to the reading following key on?? Back to basics investigation revealed that engines were not wired back to the batteries and permanently hot, another case of somebody failing to RTFM.

    New sea trials with engines properly wired gauges 100% accurate, bonus was that vessel performance now transformed, off on to the plane in six seconds. Owner is now playing hard ball on price as he is now far from sure if he wants to sell.

    Finally remember the poster a month back who had his Bosch CP3 common rail pump replaced on a Volvo D4 without proper diagnostics, and then the issue returned after owner shelled out on a new pump? Well I was contacted just the other day and asked to report on an identical set of circumstances with a Volvo D6. This one was going nasty and a report was required in order to go legal to recover costs from tec who had left his brains in his tool bag., No insurance now and losing my fire to fight battles for owners when surrounded with prejudice and stupidity.

  9. #39
    Join Date
    Dec 2001
    Posts
    1,967

    Default To David Jackson

    Quote Originally Posted by davidjackson View Post
    Hi guys, my boat has a big stick in the middle so I hope you'll allow me to contribute on this foreign forum!

    I worked for the world's largest turbo manufacturers for 20 years and I'm an engineer so I think I'm qualified to comment.

    Modern turbochargers are an integral part of the engine and have the same life requirements. They do not "kick-in". There is a fundamental mis-match between a reciprocating engine and a high speed rotating device. Over the years, advances in compressor and turbine stage design plus other technologies, such as wastegating and variable geometry, has made "lagg" almost imperceptable.

    Superchargers, regardless of type (the humble roots or one with internal compression) are generally capable of increasing air density sooner (on the torque curve) than a turbo. That's their one advantage. Most everything else about them is a disadvantage. Most significantly, they have very high parasitic losses (there are inefficient). Read "fuel consumption".

    Most marine engines are derivatives of the basic road going version. This is mostly an economies of scale thing. They'll have a number of power ratings from "work boat" through to "leisure". A rule of thumb higher power equals lower life and hence a workboat will be rated, say, 200 bhp and the leisure version will be, say, 300 bhp.

    Engine output is generally limited by air density (not fuel - it's easy to supply more fuel). Naturally aspirated diesels near enough do not exist anymore. Turbocharging increases air supply. Compressed air is hot. Intercoolers then cool the hot air and from school boy physics you'll recall that cooler air is more dense, hence more oxygen for combustion.

    Turbos are very reliable! All they ask is decent, well filtered oil and a good filter to the air inlet. Modern engines are designed to get oil to the turbo bearing as quickly as possible and the base engine will have been tested for oil supply time at something like -30 deg C.

    It's true that once the engine stops, the oil circulation will stop and the turbo may still be spinning. Again, it should be designed to tolerate this but common sense should prevail when stopping an engine (let it reach idle first).

    Hot shut down is about as bad a thing that you can do to a turbo. Not only will it be starved of oil, as above, but any residual oil may break-down by the heat and form carbon. Carbon deposits will kill the bearing in no time at all.

    Many turbos have water cooled bearing housings for just this reason.

    Water cooled turbine housings are used to meet "external touch temperature" requirements. It's contradictory to cool the turbine because it takes its power from M.Cp.delta T (basic law of thermodynamics). By design, it's nearly impossible to stop thermal cracks appearing over time. The exhaust gas may be 800 deg C and the outside touch temp may be little more than 50 deg C. Nothing to do with KKK using poor quality iron (although it did make me smile).

    A marine engine is likely to run at sea level only. A truck engine may have to pass over a mountain range. As the engine gains altitude, the air density will be lower and hence the turbo will try to work harder to generate the same power. To an extent, turbos give a degree of altitude compensation.

    The number of times you hit the throttle, how much load you're carrying and how long you run at said speed all gets computed to form what's called a Duty Cycle. Life is always based upon the duty cycle.

    Turbos can fail from low cycle fatigue (compressor stage) or high cycle fatigue (generally turbine end) but this is well outside the scope of day to day use. Fatigue will have been designed out based upon the duty cycle. That said, a blocked air inlet has the same effect as increasing altitude so it's always worth a check.

    Foreign object damage, after lubrication, is usually the reason for failure. A bit of rag through the compressor will kill it in seconds, as would a broken inlet filter. Turbine foreign object damage by definition must have gone through the engine first.

    If anyone else has a bad word to say about turbos I'll make you sail at 5 kts while standing 20 degrees away from verticle
    Fantastic Explanation David! it really was very interesting and I am happy to say that I conform to all your explanations as to what a Turbo needs to stay healthy! perhaps thats why I have had ten years of trouble free turbo's.
    You are very welcome on this forum at any time as far as I am concerned, I don't pretend to understand everything you say, but you obviously know your turbo's!

    May I wish you safe sailing and fair winds,

    Barry

  10. #40
    Join Date
    Jul 2003
    Posts
    1,564

    Default Turbo failure

    I`m sure that you do this anyway but ensuring that the engine is closed down gently (and not revved up and immediately switched off i.e. lower the revs to the lowest and wait a while until the turbos slow to their slowest possible speed) before turning off. It might also be worth taking the oil supply pipe to each turbo off at each or alternate services, and inspect and possibly clean out if necessary.
    IMHO hope this helps
    Rob

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