Efficient electric boat

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

  1. papawoodie
    Joined: Jan 2003
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    Location: South Carolina

    papawoodie Junior Member

    Thoughts on Jeremy's Hinged Prop Idea

    Jeremy,

    In reading through all the posts in this thread, I was
    pleasantly surprised to see your tilt up prop idea back
    in Post #149...

    Years ago, I was considering altering the 'Idaho' design
    (from Phil Bolger), for an electric drive system.

    The boat has 2 beavertails on the stern, that I thought
    would be useful as 'pods' for electric motors. Like you,
    I was looking for tilt-up ability, to gain access to the
    underwater drive parts.

    Rather than using hinges, I devised a rotating concept
    that pivoted the beavertails outboard to an above water
    vertical position. As a bonus, the possibility arises that
    pivoting the tails would also provide a means of steering.

    Under normal forward operation, the tails just clear the
    surface of the water. I designed the tails to be hollowed
    with a curved upper surface, leaving the sides of the tail
    to be faired slightly. Turning would bring either the port
    or starboard edge down into the water at an angle.
    Increasing the turn, brings more of the tail into the water
    for a tighter radius.

    Seeing your flip up plan, reminded me of my old drawings.
    However, since yours is more of a slipper stern, to adapt
    the concept, would involve some more thinking.

    Really love all the ideas you've processed through.
    The design has improved quite well and has led me
    to begin developing some new ideas of my own.

    I'd like to 'borrow' you U-Joint idea and combine it
    with Rick's flex-shaft. I'm drafting a long thin hull with
    two stabilizing amas. The driveshafts would pass thru
    the 'wings' to U-Joints, then connect to the unsupported
    prop shafts. A final detail involves building a 14 to 18
    inch tunnel in the aft section of the amas. I envision
    elongated 'stirrups' attached to short bronze tubes that
    would serve as supports for the shafts, where they pass
    out of the amas. These would pivot in a fashion similar
    to a kayak's rudder. In normal operation, they would be
    in the forward position, clear of the water. Levers in the
    cockpit, would swing the stirrups down and back. In the
    rearward positions, the shafts could be used for reversing.
    Or when fully extended, they would raise the shafts to
    the waterline (for beaching).

    The plans are still rough, but I'd like to be able to have
    the motors disengaged by the action of the levers, then
    to have reverse activated when the prop shaft supports
    are properly extended (and again disengaged when fully
    extended up to the waterline).

    Keep us posted... Love the progression of ideas.

    David
     
  2. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Very many thanks for the kind words, they are really appreciated. I've been away so haven't been back to update this thread on progress, but things are moving along. The boatbuilder (www.swallowboats.co.uk) has kindly sent me the first couple of photos of my hull. It's pretty close to their Winsome pedal boat design (mentioned earlier in this thread and here on their website: http://www.swallowboats.co.uk/content/view/94/104/). Changes include making the hull from thin (4mm) marine ply, removing some of the heavier parts of the structure and slightly reshaping the hull, by lowering the sheer slightly and altering the shape of the bow a little. The result should be a much lighter boat, but one that retains the good stability and low power requirement of the original. Here are a couple of photos of the hull (it's still a work in progress and doesn't have the deck or transom fitted yet).

    [​IMG]

    [​IMG]

    I am absolutely in love with the shape of this boat, it manages to combine the efficiency I've been looking for with the elegance of a slender slipper launch.

    The motor drive unit will fit through a centreboard-type slot and case built in to the base of the stern compartment and accessible through a transom mounted hatch. To disguise the hatch I'm looking at getting a CNC carved wooden name plaque to fit on the transom, that will do double duty as an access hatch.

    The motor will tip up aft, with the prop clearing the bottom of the transom (when folded) and rising up out of the water. Normally the prop and drive leg will be completely hidden from view, but having it tip like this will reduce draft for beaching and allow the prop to be checked or cleared of weed (if needed) by simply leaning over the stern (this is a calm water river boat).

    I'll be working flat out over the next few weeks to complete the boat for the summer, so may not get too much time to check in here with updates. I'll try and post at least once a week if I can, though, because I know I've been a bit tardy at times with updates!

    Jeremy
     
  3. Guest625101138

    Guest625101138 Previous Member

    Jeremy
    Have you done any tank testing of the prop and drive leg?

    Rick
     
  4. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    I've not tank tested it, Rick, but have taken it out on a canoe to get an idea of it's performance. The canoe was a 16ft plywood one and we just strapped the leg on the side to see how it worked (this was with the Mitrpak gearbox, rather than the double universal joint, but the reduction ratio was the same).

    Although I wasn't able to get any solid data to show thrust vs power, I did manage to confirm that the unit pushed the canoe along very well whilst only using about 85 watts. The losses are lower in the UJ version, so I think that I'm probably on track to achieve my target of a cruise power of less than 100 watts. The resistance of the hull above should be only slightly greater than that of the canoe, I believe, although I don't have the canoe resistance data to do an accurate comparison.

    Once the hull is finished I shall be able to do some fine tuning of the propulsion system. I've built in the ability to read prop rpm, so I should be able to do some proper measurements to see if the predictions match reality. The hull now has the deck and coamings fitted and is looking even better. With luck it will be ready for motor installation in around two weeks or so.

    Jeremy
     
  5. Guest625101138

    Guest625101138 Previous Member

    Jeremy
    Testing on a canoe is better than a tank.

    Were you happy with the way the prop folded?

    Also did you try reverse?

    Rick
     
  6. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    The prop folded OK as soon as power was reduced, and popped out very quickly as soon as power was applied. It was fine when going astern, and seemed to stay fully deployed when full astern. It wasn't so good when going astern to slow the canoe down, though, as it tended to only unfold partially when the canoe still had some forward speed.

    The one slight problem I found was that if the prop stopped with the blades vertical the lower blade just dropped down. I've thought of adding some sort of indexed prop lock, to hold the prop blades horizontal when the power is removed, but will wait and see if this is a real problem once I have the unit installed on the boat.

    Jeremy
     
  7. pistnbroke
    Joined: Jan 2009
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    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    have followd this thread for a while on the electrical side but I think I can make a few comments on the stitch and glue which may help others ...too late for you geremy the boat is built.
    If you substitute thiner ply in an attempt to save weight you have to add more fibreglass to get stiffness..look at your shearline....ply floats fibreglass does not. 6mm would have been a better choice,
    Put all your fibreglass reinforcement on the inside and only cover the whole outside with one (or two) full layers of cloth . If you put strips of tape on the outside its very difficult to get a good flat finish ...you got lots of sanding and filling to do on the sides geremy if you want it to look good. With the cable ties always fully bury them in the filler (use a spoon) or fill between them and pull them out then fill the spaces .In my view the bumps at each tie look unsightly..I would take an angle gdrinder to the top of each .pull it out and spot epoxy.. 2 x 2 blocks and screws are easier to use than table ties . Am sure you wont take offence this is a learning exercise. The best site on stitch and glue is Hannu's boatyard ( google)

    Just noticed its not you doing the building ...so great you dont have to do the sanding !!!!
     
  8. Jeremy Harris
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    The hull is really much, much better finished than those very early photos of progress show. For an idea of how she will look, here are some photos of the pedal version, built by the same company. My version is very similar, but with bigger decks and a smaller cockpit, so that I can get more solar cells on the deck.

    [​IMG]

    [​IMG]

    [​IMG]
     
  9. mental_boy
    Joined: Jun 2010
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    Location: Oakland, CA

    mental_boy Junior Member

    Jeremy, that is one elegant looking boat. Sort of an efficient, utilitarian look. I want one.

    Now for my half baked electric boat plan:

    1. Get some Fisher Paykel smartdrive washing machine motors. These motors can put out about 1hp at 600 rpm with >90% efficiency. No reduction drive needed. Note the wattages quoted are per coil, multiply by 3 to get total wattage:

    http://www.cogenmicro.com/pdf/Fisher_and_Paykel_Smartdrive_Motor_2.PDF

    2. Kidnap an electrical engineer and force them to build a custom, high voltage 3 phase AC motor controller to drive the motor. If the voltages required are too high, rewire the stator:

    http://www.yourgreendream.com/diy_fp_rewire.php

    3. Buy a pallet of LiFePO4 batteries and wire them in series to get the high voltages required.

    4. Build an efficient hull and hand made prop to accommodate the motor.

    5. Try not to electrocute yourself.
     
  10. Jeremy Harris
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    Sounds reasonable. I looked at the F&P motors (I have one here that I've played with at low voltage) but, although they are OK for direct drive, they are a bit too big a diameter to fit into the sort of boat I wanted.

    Rewiring them for low voltage is easy, just a matter of reconnecting the windings in parallel rather than series.

    Another option for low speed, high torque, direct drive is a geared electric bike hub motor, stripped of its gears. These are pretty cheap and there are a lot of cheap controller options (I'm using an ebike three phase brushless controller, the cost, including shipping from China, was just $43 US).

    Something like a Puma or BMC geared hub, stripped of it's gears, will deliver a kW or two easily enough and will be about half the diameter of the F&P motor.

    Anyway, I'm picking up my hull next week and it will then be full speed ahead on getting the motor and electrics installed and then get the boat on the water for some testing.

    Jeremy
     
  11. papawoodie
    Joined: Jan 2003
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    Location: South Carolina

    papawoodie Junior Member

    Rick,

    I've been following several different threads involving efficient hull design to optimize either pedal power or electric motors.

    Your various comments and participation have always impressed me.

    I'm no engineer [in fact, many of the discussions take me several readings to even vaguely follow].

    If you have some time, I'd like to 'pick your brain' a bit...

    I'd like to see if its possible, using good design, hobby motors, and 24 - 36 volt battery banks, on a lightweight stabilized monohull, to achieve a 12 to 15 knot speed for a 35 mile race.

    Could a Mars or Turnigy motor be located in each ama/sponson, driving flexible shafts?

    If overall length was kept under a maximum of 32 feet, what would the optimal hull look like? How wide would the stabilizers be spaced? I envision a sit-in version of your V14, or Greg's 24 hour boat, stretched longer and slightly wider.

    And I'd be interested in exploring a weird concept of obtaining some lift, at speed, from the support arms. Perhaps a Dacron covered airfoil wing shape between the hull and the sponsons...
    If it were possible to generate more lift than drag, at speed, the hull would 'operate' lighter in the water, gaining efficiency.

    Again, if you have the time, could you give this some thought towards what the optimal design might entail?

    Any help or ideas or suggestions would be greatly appreciated.

    Many thanks, in advance,

    David
     
  12. Guest625101138

    Guest625101138 Previous Member

    David
    Rather than confuse this thread with another boat with different operating requirements it will be preferrable to start your own thread.

    I expect you would be better off with a single motor unless you want system redundancy.

    To give you an idea the lowest drag hull of 200kg displacement requires 1.45kW on the hull to do 14kts. This would translate to a little over 2kW at the battery with an efficient propulsion system.

    To do statute 35miles you willl need to run for over 2 hours. So say 5kWh of batteries. A lithium battery would weigh about 50kg. So if the pilot is chosen with weight in mind a 200kg boat is feasible.

    Start a thread and place a link here so I see it and you can get into more detail.
     
  13. papawoodie
    Joined: Jan 2003
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    Location: South Carolina

    papawoodie Junior Member

  14. Jeremy Harris
    Joined: Jun 2009
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    Location: Salisbury, UK

    Jeremy Harris Senior Member

    I've just got back from a drive across country to the far side of Wales to collect the hull. I'm really pleased with the way it's come out, the Nick and Colin at Swallow Boats have done a superb job, and it's still reasonably light. Here's a couple of pictures, although bear in mind that it's not painted yet:

    [​IMG]

    [​IMG]

    After 9 hours driving today I'm off for a beer and some sleep!

    Jeremy
     

  15. Guest625101138

    Guest625101138 Previous Member

    Looking forward to see it on the water under electric power.

    Rick
     
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