Efficient electric boat

Discussion in 'Boat Design' started by Jeremy Harris, Jun 22, 2009.

  1. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    how much lower? Is the prop working behind or below the keel?
     
  2. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    so lower it down and turn it around to face forwards....are you sure you have the prop turning in the right direction as it would on an aero motor??
     
  3. wardd
    Joined: Apr 2009
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    wardd Senior Member

    would a spinner help?
     
  4. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Thanks for the interesting post. Comments below.


     
  5. bapou
    Joined: Aug 2009
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    bapou Junior Member

    Thank your for your helpful comments.

    Tonight I will test it with the reversed propeller (as it is very likely backwards now), and make a photo
    of the motor in its running position. I still have to add a spinner; I lost one during the first try as it was only fixed by one screw in the middle which came loose by the torque.

    The propeller choice was from drag calculations by Rick (earlier in this forum)
    and Javaprop calculations.

    as I remember

    4 knots (~7.5km/h), 40N drag
    0.31x0.22m propeller (don't have the RPM in the moment and have to recalculate)
    110W input to propeller, according to the motor efficiency of only 70% at this power, this would correspond to 150W input to the motor.

    5 knots (9.18km/h), 84N drag
    0.31x0.17 m propeller, 1000RPM
    290W Input to propeller.. this is not realistic anymore with the present state of motor and controller, as the motor efficiency drops to 50%... and the RPM drops to <500W


    The aim now would be to meet the first 4knot~150W motor input aim... by modifying the propeller, mounting, spinner, controller programming etc...


    Thom
     
  6. bapou
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    bapou Junior Member

    I did some more testing; unfortunately it got dark and I couldn't make
    many measurements.

    Mounting the propeller in the right direction gave a strong improvement!
    Here is the data I have:

    12x8, CAM Carbon Power Prop.
    100W Motor Input (= roughly 70W Propeller Input), 600RPM, 6km/h (1.66m/s)

    maximum Motor Input 320W (roughly 170W Propeller Input), 800RPM 8km/h

    I have to put these numbers into Javaprop, but it looks like I'm getting closer to Rick's drag predictions.


    @daiquiri: The photo shows the approximate position of the propeller used in the tests. I'm looking forward for suggestions... (changes in the depth, keel shape, distance.. etc.)
     

    Attached Files:

  7. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Check out post #252 McDennny on this list for some more improvements. You were following this work and may have forgotten about some of these tricks. Your motor alterations alone should be getting you much better efficiency than the crude brush troll motors. I suspect maybe something is not quite right with your rewinding of the motor and you are sacrificing a great deal of torque somewhere...

    The block of motor in front and keel projections from the hull are affecting your prop access to undisturbed water. Still, you should be getting much better efficiency despite this with the type of motor/controller you are using...

    Access to undisturbed water way behind the boat is another reason I prefer flex shaft configurations running without a skeg in longtail fashion....

    Porta


     
  8. bapou
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    bapou Junior Member

    Hi portacruise,
    thanks for your comments. I carefully read McDenny's very useful tests; I just didn't have time to implement everything. My next steps will be fairing+Spinner, as well trying out different propellers. This should give some more improvements.

    In the moment my results are close, and maybe slightly more efficient than McDenny's tests:
    without fairing, McDenny used 260Watts (Controller Input) for 4.3mph and according to an graph in one of his older posts about 150Watt for 3.8mph/ 6km/h
    My tests show 100Watts for 6km/h but I don't know how our hulls are comparing.

    The main problem in my case is the motor+controller efficency (see the Motor efficiency graph I attached in my recent post). Increasing the number of turns/windings in the motor in order to make it turn slower makes it less efficient. I doubt that there is a problem in the windings on my motor; it is more a general construction problem that one cannot get this kind and size of stator to run slowly at high efficiency (this opinion results from my discussion with the motor specialists like Ralph from powercroco).
    This results in efficiencies of 60-70% of motor+controller compared to 80-90% that one could ideally get.

    My next steps will be to work again on the solar cells. Than, (somewhere next year) I would try an inboard type with maybe with a flexible shaft, as this would give me more flexibility in switching the motor and a better hydrodynamic propeller setup.
    I'm looking forward to Jeremy's test.

    Thom
     
  9. portacruise
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    portacruise Senior Member

    Hope the comments below are of some help.
     
  10. tinkz
    Joined: Jan 2011
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    Location: indiana

    tinkz New Member

    its been about 2 years now.. I'd "liberated" a motor from a wrecked "freedom scooter" is a lot like those electric skateboard-scooters. it was about 4" diameter 10 pole 24vdc motor rated at 250 watts power and 2500 rpm. low on power consumption and very BIG on torque. I ran it on 12vdc, direct coupled to a 5/16 shaft that was a *perfect fit to 3/8 hard brake line tubing that I gave a gravity oil tower to with some fiberglass grafting.. (*it literally floated in oil with .005-.006 clearance)
    -all that to a prop from http://www.youngprops.com/ -theyre worth looking at!

    it turned about 11-1200 rpm on 12vdc, maybe pulled 130 watts, never hooked up meters to the thing to know exactly, but it was pretty efficient.

    motor, shaft, brake line stuffing tube, and prop, was maybe 35 bucks spent total was pretty easy too. not a "fast" spinner, but the torque was sure there! what is this thing I keep hearing about? speed controllers? (I used a household light switch!)

    this went into a narrowed variation of a "Bebop" from the svensons.com site, intended for electric power and kids to get out and play in. it had a cheap little old car stereo and the speakers were from an old monster console.. 2 10" woofers and 2 2x6 horn tweeters were built into it, loud as all hell so the fishermen would hate it of course. funny stuff.

    just mentioning this toy I'd built because of what it had in it for its drivetrain, that type of motor-driveshaft-prop might be a good option for someone else who likes to fiddlephart with these kinds of electric toys.
     
  11. tinkz
    Joined: Jan 2011
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    tinkz New Member

    for bapou.. the kids boat I'd slapped together, the motor ran a little faster stronger clockwise than counterclockwise, its a "motor timing" thing, so I just ordered the appropriate direction prop for what I saw happening. no insult intended to what you've got going on there, the kids boat would have performed even better with a different style and longer hull shape no doubt, but it ran a pretty good 4 mph with the drivetrain as described. it was built for "cute" not "efficient", I know it was plain luck that the thing muscled around so well. it was built 7'8" long, flat bottom, flat transom, so it could stand on its end to save space in the garage through the winter months.

    a better longer narrower hull, I'm sure the motor could deal with a larger prop, or more voltage to the motor, or both, it never warmed up at all on 12v
     
  12. yellowcat
    Joined: Feb 2007
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    yellowcat Junior Member

    4 mph is quite interesting, did you have a wind factor ? you can beat 4mph with backwind, especially if you have a little viking sail or kite at bow. I find the electric motors accompany us up to a certain point, after that it can become a genset.
    i am looking at a design for a hoverflyingdingy concept. Efficiency is all over the constraints list, with lithium batteries coming, and HHO hybrids, we might see new stuff flying "below" our head . it can be quite an accomplishment to see a kite/hovering/moth on foilers. I guess it will not hover for long. Next summer, we will try my big kite on the dingy with an electric motor we got for cheap.
     
  13. hexadrone
    Joined: Jan 2011
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    hexadrone New Member

    Jeremy Harris help request

    Hi Jeremy Harris please i need your help please .
    I have one problem with one brushless motor .
    Please contact me in PM .Thank you in advance for your help .
     
  14. Submarine Tom

    Submarine Tom Previous Member

    Try Jeremy at endless-sphere.com or PM him by left clicking on his name.

    -Tom
     

  15. hexadrone
    Joined: Jan 2011
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    hexadrone New Member

    i dear , do you have e mail of him ? You can contact him and tell him I need his help? I like getting this far
    thank you
     
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