Converting Waverunner to Diesel

Discussion in 'Propulsion' started by shaw22, Jul 9, 2012.

  1. shaw22
    Joined: Jul 2012
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    Location: Chicago, IL

    shaw22 Junior Member

    Greetings from Chicago,
    Can I put the attached diesel engine on a yamaha xl800 whose motor is blown. The diesel engine will cost less in fuel to operate. But I see the rpm 3600 much lower than the gasoline engine. Would I be able to do 50MPH with the diesel motor ?

    If the xl800 is too big, are there smaller models of pwc (yamaha or other brand) that I can use this diesel motor on ?

    Have anyone tried to convert into diesel before ?

    Thanks
    Shaw
     

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  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yes, you can install it. No you will not see anything close to 50 MPH and yes the RPM issue will cause issues, not to mention the power to weight ratio.

    You really can't possably expect much, changing from a 120 HP gas engine to a diesel engine, that has over an 80% reduction in available horsepower, can you? It's a bit like asking if you transplant a Pinto engine into a Corvette and still expect 150 MPH . . . You have to be reasonably close to realistic I'd think.
     
  3. shaw22
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    shaw22 Junior Member

    Thank You Par.
    Could I look into the possibility of a high rpm A/C electric motor and then powering it from a compact diesel generator ?
    I am a newbie, so thanks in advance for being patient with me
     
  4. shaw22
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    shaw22 Junior Member

    The way I look at it, the impeller has to spin at high speeds - 7000 to 12,500 rpms, but wont be requiring high torque as it is impelling flowing water
     
  5. PAR
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    PAR Yacht Designer/Builder

    Kilowatts is kilowatts regardless if converted to horsepower or not. I'm not sure what your background is, but adding a less efficient rotational force (diesel/electric) isn't going to permit a smaller drive option, without considerable output loses as well.

    Simply put, you currently have a 120 HP engine and pump. A 22 HP diesel can spin up a 15 KW generator head under full load. Not considering the weight issue, which is considerable, you'll never get anything near the power necessary (motor size) to spin up the pump at similar speeds, with the available force necessary for the previous preformance envelop (not even close).

    You'll need the diesel, which is heavier then the gas engine at a fraction of the HP. A powerhead, which will be another 100+ pounds, a motor which is another 100 pounds, controls, starting battery (another 50 pounds) and assorted accessories. All to have half the preformance (if you're lucky) of the previous arrangement? How much work do you think the 120 HP gas engine is doing at 50 MPH? It's not loafing along, it's literally laying down every ounce it can. It's not a car, which when up to speed, can ease way back on the throttle and scoot quite well. It's a continuous duty cycle engine and substantially different in this regard.
     
  6. shaw22
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    shaw22 Junior Member

    Thank You again Par.
    I am an American of Bangaladesh heridity. We are trying to setup a non-profit Marine Sports Club in Bangladesh. Government taxes are less on Diesel and it is 42.22% cheaper than gasoline. (US$1.09 per liter for gasoline / $0.63 per liter for diesel). So there will be a huge difference in operating cost. We don't want to get the Chinese PWC's as they seem to have a bad reputation. So our goal is to get 10 Waverunners (or any other good brand, all 10 same manufacturer/model) (with blown motors) from USA and then ship them to Bangladesh and convert to diesel.
    I understand your point, it don't make no sense for someone to convert it to a diesel in USA, hopefully you see my rational now
     
  7. shaw22
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    shaw22 Junior Member

  8. PAR
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    PAR Yacht Designer/Builder

    I just quickly looked at the Eco site and it's classic horse crap, full of miss-statements and ridiculousness. There's a good reason they don't have electric front end loaders or jet fighters and if you do the math, it's pretty obvious why.

    Punch up the numbers yourself and see where you come out, but the gas engine needs 120 HP for 50 MPH and does so with a reasonable power to weight ratio. How much do you want to bet you'll need a fair bit more HP (likely double) to see the same speed with a diesel/electric?

    Lets look at the biggest issue you'll have to over come; weight per HP. The pump, gas engine, fuel and start battery on your jet ski is a 400 pound package, which is 3.3 pounds per HP and this produces 50 MPH. Now, take a 300 pound 20 HP diesel, add 60 pounds in fuel, 125 pounds in 15 KW generator head, 100 pounds in a 15 KW electric motor, another 100 pounds for controls and start battery (685 pounds total) and this ends up being 34.25 pounds per HP! the math is pretty simple. So how fast do you think the 34.25 pounds per HP is going to push this little boat, particularly compared to the gas version, that has a 3.3 pounds per HP setup?

    Again, there's no free rides when it comes to power production, regardless of the setup. It's all about power to weight ratios and currently the electric folks, are trying to get around this with batteries instead of a powerhead, such as you've envisioned. The only problem is batteries weigh a lot too, so to get any reasonable range and/or preformance, you have to carry a diesel's weight worth of of batteries, which ends up doing the same thing, though with much less noise, smoke and vibration.

    A classic example is the Tesla sports car. Yep, it goes like scalded dog and rivals the worlds gas powered sports cars, but only for about an hour, before it loses enough zap in it's batteries to so dramatically reduce it's preformance, that's it's just not practical, because it needs to sit on a charger for the next 10 hours. And this is using the best of the best (okay, well pretty darn good anyway) in regard to controls, motors, batteries and engineering.
     
  9. shaw22
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    shaw22 Junior Member

    Thank You Paul, I am convinced now. Will have to stick with the gasoline engine s.
     

  10. fredsnotdead
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    fredsnotdead Junior Member

    Actually for cars the E technology doesn't even compare and the Tesla is a very poor over-glorified example of that.
    And, some of the major manuf.(GM or Buick) have taken some tiny and simple steps towards E that could and should have been done long ago whereas the engine shuts down and runs on battery power instead of idling.

    But for boats, you're exactly right because the parameters are totally different. I want to have a VERY limited use E powered pontoon, and weight isn't an issue because it will be very stripped down, not only that we don't now or intend on motoring any farther than what little that we do now(1-2 miles total). Also, the cost is minimal because I'm going to use used-but- operable golf cart batteries that are free and all I have to do is install and return them.
     
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