Converting an Outboard to Diesel.

Discussion in 'Outboards' started by rustybarge, Aug 26, 2014.

  1. WestVanHan
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    WestVanHan Not a Senior Member

    I've also been wondering about the 70 hp...to have a long lasting engine it's going to need to be fairly large....and quite heavy.

    Cummins 4BT and John Deere 4045 are rated about 70 hp continuous and they weigh about 600-700 pounds. And will last for many thousands of hours at 70 hp.

    Not sure how long a VW will last at a continuous 70 hp.
     
  2. rustybarge
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    rustybarge Cheetah 25' Powercat.

    At displ speed even a very heavy boat will not need much power to push it at 5 or 6 kts, the other 50hp may come in handy against wind and tide.

    Even so the lightest Yanmar 2ltr diesel still weighs 220 kg, that's a lot to bolt on top of an outboard leg, plus the 90 deg gearbox.

    The OB leg is going to have to BIG.....
     
  3. WestVanHan
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    WestVanHan Not a Senior Member

    rustybarge

    About 60-70hp approx output to push at hull speed.

    So you don't want to run at hull speed all the time?
     
  4. rustybarge
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    rustybarge Cheetah 25' Powercat.

    It would be very nice to cruise at hull speed, but am I right in saying that it takes nearly twice the power to go from 5kts to 7kts.....?

    I have the specs for the equivalent Yanmar 2ltr turbo which weighs 217 kg:
    http://www.yanmarmarine.eu/theme/ya...sure - datasheet/English/Yanmar-4JH4-HTE1.pdf

    1900 revs 70hp at 5 ltr/hr
    2600 revs 100hp at 12ltr/hr

    ...that pretty impressive for tiddly little 2ltr engine.
     
  5. WestVanHan
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    WestVanHan Not a Senior Member

    Depends on the boat....
     
  6. rustybarge
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    rustybarge Cheetah 25' Powercat.

    Here in Europe most marina charges start at 'up to 12metres' in most places.
    12-15mtrs is 50% more, 15-18 mtrs double the 12mtr price!

    People get paid half as much as the states, but everything costs twice as much.:mad:

    ....so it would have to be a 11.99mtr boat.:D
     
  7. rustybarge
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    rustybarge Cheetah 25' Powercat.

  8. powerabout
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    powerabout Senior Member

    Now thats got potential for an outboard diesel
     
    Last edited: Jan 14, 2015
  9. rustybarge
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    rustybarge Cheetah 25' Powercat.

    I think the biggest problem with a 2 stroke diesel is scavenging the exhaust out of the cylinders successfully, and I'm wondering what sort of continuous duty cycle such a small capacity engine can manage?

    730cc diesel: 30hp?
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Two-stroke diesels were notoriously noisy, probably due to being fitted with blowers to clear the exhaust, I wonder how they may have beaten that.
     
  11. powerabout
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    powerabout Senior Member

    Piston 2 stokes need some kind of forced scavenging
    Now that we computer controlled injection and valves ( large ship engines and cant be far away on small engines) tons of stuff being re looked at.
    Poor exhaust scavenging is a bonus as yet are getting EGR
    This might only sound like a normal rotary but lots more torque?
    Look at E-tec outboards, they produce less emissions than 4 stokes in most conditions
     
  12. rustybarge
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    rustybarge Cheetah 25' Powercat.

    I had a small 2cc Diesel engine on a model aeroplane when I was young; it had no scavenge pump but I think it had a port cut at the bottom of the cylinder to evacuate the exhaust. but I do remember that a massive amount of 'goo' came out of the engine and covered everything with slippy slimy unburn fuel.

    ...I also remember it was a pig to start.:D
     
  13. powerabout
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    powerabout Senior Member

    but after you install the correct exhaust they are very quiet and smooth
    The exhaust valves open earlier than on a 4 stroke hence you get some of the bang out the exhaust.
    The old commer knocker design is also being re looked at
     
  14. essenmein
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    essenmein Junior Member

    Interesting is the statement on thermal efficiency, 35% for 4stroke, 50% for teh two stroke.

    Re scavenging, 2 stroke diesels can not be crankcase aspirated since that has to be lubricated with oil which would cause all kinds of problems with combustion. In the very largest engines you can build sealed bearings, but not practical smaller. So these will be like the Detroits, super charger or turbo to blow the exhaust out when the intake ports are uncovered when the piston is at the bottom of the stroke. Funny that Detroit calls the engines with a roots blower to give barely above atmospheric boost "naturally aspirated".

    Cool little motor though! Also interesting only rated to 1500rpm...?
     

  15. WestVanHan
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    WestVanHan Not a Senior Member

    Cool little engine,but remember that as a 2 stroke it is in reality a 1.5 litre 4 stroke packaged differently.

    If one wants efficiency go for opposed pistons,IIRC the Jumo engines were the most efficient engines built until the modern piezo/30,000 psi TDI engines.
    Hard to put in an outboard....

    http://en.wikipedia.org/wiki/Junkers_Jumo_205


    Power output: 880 PS (868 hp, 647 kW at 2,800 rpm
    Specific power: 39.0 kW/L (0.86 hp/inĀ³)
    Compression ratio: 17:1
    Power-to-weight ratio: 1.09 kW/kg (0.66 hp/lb)

    Napier:

    http://en.wikipedia.org/wiki/Napier_Deltic
     
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