reasons not to use high-performance diesels

Discussion in 'Diesel Engines' started by Joris, Mar 25, 2013.

  1. Joris
    Joined: Mar 2013
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    Joris Junior Member

    First of all, my apologies for my bad english, if i'm making any mistaken please don't hesitate to correct me.

    So the question; Is there any reason the light high performance diesel-engines are not used in boats? While i'm still a long way from fitting one (building 18' wooden powerboat), i'm kinda looking around to see what i could use when my boat is ready and i've noticed that most marine diesels over 100HP are 6 or 8 cylinders and quite large compared to the ones i'm used to working on in european cars.
    Some may wonder why this is such an issue to me when V8-turn-key engines are cheap...well, i live in belgium where gas costs 1,7euro/l (roughly 8,5USD/g) so the idea to have a 2.2L 4cylinder biturbo diesel that produces 170hp and over 300lbsft of torque seems very interesting.
    Am i missing something?

    1 person likes this.
  2. gonzo
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    gonzo Senior Member

    The service of an engine on a boat is much harder than in a car. A car accelerates, using high power, and then maintains speed using 50-60 HP. A boat uses much more power all the time because it displaces water to move. It would be like loading a car with a heavy trailer and going uphill at maximum speed for hours on end.
  3. Milehog
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    Milehog Clever Quip

    Boat and truck engines have to work harder than car engines. Look up duty cycle.
    In your car the engine pulls hard to accelerate to speed then you back off to maintain the speed. A boat engine is pulling hard the whole time the boat is on plane.
    In other words the boat has to work harder to maintain cruise than a car does.
  4. Milehog
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    Milehog Clever Quip

    Dammit Gonzo! You type faster than I do!
  5. Joris
    Joined: Mar 2013
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    Joris Junior Member

    For my boat i think around 100hp will be sufficient. I've seen these engines on testbenches running full load for several hours so i'm pretty sure they will last at 60% with mechanical issues if the modifications on ECU, engine-cooling, exhaust etc are done correctly.
    I've seen plenty engines that are less powerfull from pre-ECU-era like the XUD 1.9 and Ford 1.8 but for some reason everybody stays clear of the modern engines with the only exception beeing a 2.5 Audi/VW V6 TDI that costs about twice as much. The strange thing is that most enginebuilders seems to think it's actually a good idea...
  6. tomas
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    tomas Senior Member

    You've been Ninja'd!
  7. jonr
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    jonr Senior Member

    I think that a lightweight car diesel could work in a boat - but I'd operate it at something more like 40% of max output.
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Operating a diesel at 40% of capacity will not favor it's life span. Continuous duty engines (boats, planes, generators, etc.) are designed to run at a specific RPM and load range. Lugging an engine well below this will just kill it prematurely.

    Your best choice is to match your expected performance envelop with the engine and drive assembly. This means matching a reduction with an engine and prop combination that will produce the desired results.

    Automotive conversions are possible, though usually more costly and often not as well suited for continuous duty cycles, without changing the cam.

    It would be more helpful if you told us jato design you where building, so reasonable suggestions as to what drive train and engine options are suitable.
  9. yipster
    Joined: Oct 2002
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    yipster designer

    Joris, you mentiont a VW, it might be interesting to compare to a VW marine diesel
  10. jonr
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    jonr Senior Member

    Yes it will, we aren't talking about continuous duty rated engines and operating at 40% of capacity is in no way "lugging" (it's well within the rated range).
  11. phillnjack
    Joined: Mar 2013
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    phillnjack Junior Member

    What diesel engines in boats are the marine engines then ?
    name 4 marine diesels under 10 litres that are made for marine use.
    before you do name them, do not even think about mercruiser or volvo penta !!!!!
  12. El_Guero

    El_Guero Previous Member


    I think you are missing something in your equations.

    You will save about .15 € per liter on fuel costs.

    I am expecting you will spend about 1,000 € for your diesel conversion.

    If my numbers are close, you will need to burn 7,000 liters BEFORE you BEGIN to break even over a gas burner .... And that is ignoring the efficiency differences of the two types of fuels for the moment.

    I am guessing 7,000 liters would be at least 7 years of enjoyment BEFORE you would even begin to break even ..... compare costs including interest and the different efficiencies, and you might never break even.

    Unless someone gives you the diesel engine and helps you install it, it might not be worth the conversion effort.

  13. CDK
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    CDK retired engineer

    Joris, the presumption that modern automotive diesels are not used in boats is wrong.
    There are Fiat, VW and BMW turbo charged engines and what Steyr in Austria builds has the same performance level.

    The fact that you see so many dinosaur engines installed in boats has to do with both fear of electronics and profit margines. Passenger cars form a very competitive market, where large volumes and a minimal profit are normal, in the marine world it is the other way around. If a boat builder would offer his products to a dealer allowing him just 15% profit, the dealer would show no interest at all because others allow him almost 50%.
    Arguments like reliability and life expectancy are of course used to justify that situation.

    Do not forget that boats are a luxury, while cars are a necessity. In some sectors, like musical instruments and jewelry, it is even worse: the dealer is offended when you offer him "only" 50%.
  14. slow fred
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    slow fred Junior Member

    I always try to work on a 10% profit margin. Example, I buy an item for $100 and sell it for $1,000, It works every time.

  15. daiquiri
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    daiquiri Engineering and Design

    This is a proof that you don't have to know the math to make money. :p
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