on highway diesel vs marine

Discussion in 'Diesel Engines' started by toussy, Mar 24, 2007.

  1. toussy
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    toussy New Member

    Is there any one who could tell me the difference between on highway diesel engine and marine diesel engine from power point of view. Comparing 300 hp on highway diesel engine with 300 hp marine diesel engine then what will be the difference in torque , rpm and internal construction . In other words can I marinize the 300 hp on highway diesel engine and have the same result as if i am using a 300 hp marine engine .....:confused: :?: :!:
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    RMSOSF Junior Member

    Depends on what engine you are taliking about. Generally, the torque curve will be different since a boat loads the engine differently than a truck. An on-highway engine also turns about half the revs at speed as does a marine engine. WOT may also differ.
  3. Mikefleetwood
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    Mikefleetwood Junior Member

    Main difference will be long-term reliability.

    A marine engine spends most of it's life at, or near, full rated power. Meanwhile, a vehicle engine spends most of it's life at a fraction of rated power. So, a marine engine will be more strongly built, with larger bearing surfaces.

    Having said that, some marine engines are marinised versions of truck engines, and they seem to have no problems.
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    LAZYJACK Junior Member

    Since there seems to be a difference, when do you know which is which marinised truck engine or "true" marine engine? Is this indicated by the manufacturer?

  5. Crag Cay
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    Crag Cay Senior Member

    The market is too small for there to be any true, built from the ground up, marine diesels engines. Economics dictates that every marine engine is based on a mother engine whose main market is else where.

    All engines have a 'duty cycle' which is an imaginary pattern of use used to predict the engine's life expectancy. For a light road vehicle for instance, that the manufacturers want to last 200,000 miles, the designers gauge what this will mean in terms of hours spent at full load, or the number of cold start ups, or the hours cruising at half revs, etc. Then they get as much power out of the cheapest engine that will then still survive this predicted 'life cycle'. In the Renault Traffic vans, for instance, they have decided that a 4 cylinder, 1.9 ltr, 4100 rpm, 95 HP, turbocharged single rail diesel engine will be durable enough, even in a commercial delivery van.

    But the 'Duty Cycle' in a leisure motor boat is always more severe, let alone the various grades of commercial 'duty cycle'. Although some components may be swapped, this increased duty cycle is generally achieved by lowering the permitted rpm, perhaps lowering the turbo boast and so restricting the HP that the engine is allowed to develop. This then reduces the 'strain' the engine is under. So our Renault engine above finds its use in the marine world as a 3200 rpm 40 something HP sailing boat auxiliary.

    And if we want say, something around the 100 hp to match our van, then in the marine world you're looking at the top end of the 4.5 litre engines from say Perkins (which would suit a sailing yacht auxiliary) and for a single engined long distance trawler yacht, you might prefer the same HP developed from a slower running 6 litre engine, such as a Lugger.

    One of the guides as to how hard an engine is working to develop a given power output, is to calculate the piston speed, and books like Bebe's give you estimates for what speed you should stay below for extreme durability. However these days with various emission regulations and lack of applications, real slow beaters are increasingly hard to find. For instance, the Gardner 6LX in continuous commercial duty rating (real tugs and trawlers) only developed just over 100 HP but this was from 10.5 litres at only 1400 rpm. No wonder secondhand ones still cost over 20,000 GBP. And there as big as a house.
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    FAST FRED Senior Member

    Since there are almost no true marine engines in small sizes (Ship diesels are different)
    just hit the mfg site to find the dyty rating you need.

    While its nice to contemplate your boat motor can run 10,000 hours at cruise , most boats only go 100 or 200 hours a year, so a "lesser" duty cycle can be selected.

    Some engines common in boats are auto take outs , and will only give auto level of service, and have no cont rating at all..

    A modern truck with a Series 60 Detroit will run 1,000,000 miles with only routine service , the autos are only specked to 1/5 or 1/4 of that.

    Detroit Cat Cummins all have "truck" engines in there "marine" catalog, any one will do fine in a boat that may see 10,000 hours.

    The car folks Yannmar , Steyer , Perkins ,Volvo all work out fine in pleasure boats .

    What do you NEED? Speed & light weight or service life?


  7. Frosty

    Frosty Previous Member

    My opinion is this Toussy.

    Truck diesels and marine diesels are close the trick is in the cooling and exhaust.
    Petrol engines are much further away from each other.

    It depends on what you want to do with it. if you want go round the world, you need a round the world engine. If you just want to chug out to sea 5-6 miles on a summer evening a truck motor will be fine.
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