Repower 34' yacht with diesel AC gen-set & VFD

Discussion in 'Propulsion' started by bluedolfin, Feb 15, 2017.

  1. bluedolfin
    Joined: Feb 2017
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    bluedolfin New Member

    I am looking to re-power a yacht, removing the twin 454 V8 engines with a single diesel engine connected to a generator with an inverter or Variable Frequency Drive to control the power load to the AC powered 3 phase motors connected to their props.

    VFD (Variable Frequency Drives) manufacturers: Gefran, Danfoss, Vacon, Siemens, Yaskowa, GE, Mitsubishi to name a few.

    VFD's are used a lot in industrial applications for smart control and energy efficiency of connected motors. Usually a VFD has input power from the local utility then it provides modified output power using variable frequency / power to the VFD adapted motors. Similar to a diesel electric train works accept they us DC.

    I would like to do this for a yacht for the benefit of lower fuel consumption, operating maintenance costs, lighter weight benefits.

    Similar in concept to this video: https://www.youtube.com/watch?v=7mj_ojHwdo4

    Has anyone done a retro fit like this on a boat around this size (25' - 40')?

    Thanks
     
  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Are you intending to run it at the same speed as what you were doing with the 454's

    What is the type of boat? Do you know what is the average speed that you are trying to target your cruise at?? Do you know what your fuel consumption/hour was at the target cruise speed?

    The link that you provided was for a slow moving barge with a 30kw/ 40 hp engine.

    If you can give us the answers we can size a suitable diesel that can sustain input horsepower to get your cruise speed achieved.
     
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    VFD's are used where variable rpm is required from 3 phase motors in industrial applications.
    Before this technology evolved, mechanical solutions were used, like hydraulics or variable transmissions.
    Acceptable efficiency only where grid power is available, not where the power has to be generated from fossil fuel.
     
  4. Sparky568
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    Sparky568 Junior Member

    You left out ABB. Probably the best in the business. Agree with CDK. VFD drives in the application you are considering will be inefficient. Are you also looking to maintain anything more than steering speed? Are you keeping the twin screws? If you are, you will need two AC motors with one drive each and a generator large enough to power both. Given your location you will need drives and motors that are marine rated. Also, unless you are in the drive bushiness, you need factory start up and calibration = $$$.
     
  5. FAST FRED
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    FAST FRED Senior Member

    Far cheaper to obtain a couple of used diesels with a deep reduction (to use existing props and shafting).

    AS a displacement boat only 30-40 hp is required m ez and cheap.
     
  6. bluedolfin
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    bluedolfin New Member

    ~~~
    Barry,

    Searay 340 - Typical cruise speed at 28 MPH at 28 GPH. Dry weight around 11,500 lbs. I would like to shoot for a cruise speed of 25 MPH by matching the diesel to a 3 phase generator, and a Variable Frequency Drive controlling the power to the two prop motors.
     
  7. bluedolfin
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    bluedolfin New Member

    Thanks CDK and Sparky,

    And ya, how could I forget ABB. ;) Well I think that about answers it. My original goal was to get more time out on the water, the high fuel consumption crimps the budget. I know larger vessels used in marine and mining applications use diesel electric propulsion systems. My hope was that as technology advances that by now it might be a more viable application for a 34' size yacht.

    What kind of technologies or re-power options would you suggest to save on fuel, assuming a cruise speed of 25MPH? Dry weight is around 11,500 lbs.
     
  8. Sparky568
    Joined: Jan 2017
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    Sparky568 Junior Member

    Sorry, but I can't think of any other than repowering with updated fuel injection if your existing engines are carb based or smaller diesel replacement as suggested above. Cummins has a very good rebuild program for boats prior to the tier ratings. But as you will need two engines you'll be spending a lot of dough for the conversion. Fuel tanks, new lines, added filters etc. Sorry to burst your bubble but that's what boating comes down to. Available cash vs. time. Just remember not all your time has to. E spent doing 20 knots.
     
  9. bluedolfin
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    bluedolfin New Member

    Thank you
     

  10. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    None. There is nothing as efficient as direct drive mechanical transmission propulsion. Ideally you would find a motor that's operating rpm allowed you to not use a reduction gear, but it would be impractical.

    If you want to save on fuel, either slow down with the same boat, or buy a trawler with a 10kn top speed.
     
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