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Thread: Solar-electric kayak

  1. #1
    Sharp Shooter

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    Default Solar-electric kayak

    I built some outriggers for my kayak for mounting solar panels (18V, 50W each). I also put together a small electric outboard motor using a motor and planetary gearbox from an 18V cordless impact driver.

    The university (NMU) held its second annual solar boat race through the canals in St Francis a couple of weeks ago. It was also the first opportunity to test the whole shebang.I did most of the race on only two active panels and a substitute prop but at least managed to keep going for the full four hours without anything smoking or melting. Average speed was 2.2kts (4kph).

    I have since had it out on the river for another 2hr test using a larger prop. Speed is up to 3.2kts which means propulsive power has tripled. The new prop is much more efficient but it also loads the motor more and gets it running closer to its own max efficiency rpm. The only trade-off is on the panels' side. Since it draws more current, it is pulling the voltage down so I am not getting rated power coming in.

    Thus far I have wired the panels directly to the motor. No battery and no other electronics in between. I will be installing a dc voltage converter next. It will feed the motor more amps at lower volts while keeping the panels pushing out max power.
















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  2. #2
    Protea Benchrest (Air) Team '13/'15/'17/'19

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    Beautiful work, your kayak looks super sleek.
    is there not a negative effect on propulsion being mounted to the side of the vessel compared to it being mounted inline with the hull?
    Last edited by Voodoo; 26-11-18 at 08:21.
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  3. #3
    Sharp Shooter
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    That looks great, and seems extremely ineresting!!
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  4. #4
    Sharp Shooter

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    Quote Originally Posted by Voodoo View Post
    Beautiful work, your kayak looks super sleek.
    is there not a negative effect on propulsion being mounted to the side of the vessel compared to it being mounted inline with the hull?
    Likely, but it will be extremely small.

    It will also depend on which way the kayak is heeling. If the right outrigger is providing stability, the drag it creates cancels the turning force due to the motor's offset thrust-line. The benefit of being able to regularly clean the prop of weeds makes up for any shortcomings compared to a stern-mounted motor.
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  5. #5
    Sharp Shooter

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    Some footage and remarks during the most recent test.

    Solar kayak - new propeller test - YouTube



    This is how the motor guts piece together-

    DIY electric kayak motor - assembly and dry run - YouTube

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  6. #6
    Protea FT Team '18/'19
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    Flippen amazing.
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  7. #7
    Springer FT World Champion '09
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    Brilliant William!

    Can 3 knots get a hydrofoil functioning?
    Last edited by Bludlust; 27-11-18 at 07:53.
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  8. #8
    SAFTAA FT Colours '18/'19
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    Amazing that that small prop can propel you at 3 knots. It looks like a drone prop?
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  9. #9
    Sharp Shooter

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    Quote Originally Posted by Bludlust View Post
    Brilliant William!

    Can 3 knots get a hydrofoil functioning?
    You have read my mind Blud. I still have to do the numbers but I think 3kts will require a very large foil for someone my size. There are still some refinements and optimisation outstanding as well as a fourth panel to add another 50W. We might yet fly...


    Quote Originally Posted by africansky View Post
    Amazing that that small prop can propel you at 3 knots. It looks like a drone prop?
    The small orange prop might very well be a drone prop (5x5") but it only got me up to 2.2kts. The motor housing is 63mm OD so there was very little of the prop sticking past to actually provide some thrust.
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  10. #10
    Sharp Shooter
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    A buck / boost converter(with correct current capacity for the max draw of the motor) and 3 x 6v 4.5amp batteries in series will work very well in your system. The 3 panels should supply enough current at a constant voltage through the buck / boost converter and when the panel supply voltage drops the battery will supplement the panels.

    The batteries will not last long, but they will fill the dips in panel supply.

    I use a buck / boost converter with my solar panels at home (without a battery) in my workshop. It drives LED lights, small battery chargers for my LIPO charger and NIMH charger etc. I even charge my Daystate with it.
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  11. #11
    Sharp Shooter

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    Quote Originally Posted by Dallas View Post
    A buck / boost converter(with correct current capacity for the max draw of the motor) and 3 x 6v 4.5amp batteries in series will work very well in your system. The 3 panels should supply enough current at a constant voltage through the buck / boost converter and when the panel supply voltage drops the battery will supplement the panels.

    The batteries will not last long, but they will fill the dips in panel supply.

    I use a buck / boost converter with my solar panels at home (without a battery) in my workshop. It drives LED lights, small battery chargers for my LIPO charger and NIMH charger etc. I even charge my Daystate with it.
    I have already ordered 2x adjustable 9A buck converters and a volt-ammeter. Besides being cheaper than an MPPT, it gives me something to do by manually tracking the panels' max power point.
    Doing sub-5kts with nothing to do but steer gets boring very quickly. There must be some knob to tune or strings to pull to keep occupied!
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  12. #12
    Sharp Shooter

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    It turns out that 3kts is not too far off the mark for foiling lift-off. Speed for take-off with lowest possible power seems to be around 3.5kts.

    The power required is however a good deal more. With a 3m x 0.2m wing you could get up on around 450W installed. Assuming prop and motor can be kept at max efficiency over the entire speed range, this power should get you to a top speed of around 5.5kts. Around the same speed as you would have reached with the same power and no foils.

    With a slightly more manageable wing span of 2.4m x 0.22m and two 335W panels, you could delay take-off until 4.5kts and hit a top speed of 8kts.

    The panels' weight is the same as a 170Ah 12V deep cycle battery. At the same total power output the battery will last around 2 hours. You could stretch that to 3hrs if you cruise at 6.5kts.

    Cost would be pretty much the same for panels or batteries, about R3300.
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  13. #13
    Sharp Shooter

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    2019's race is around the corner (7, 8 Dec, St Francis). This time I intend to be more than just a ride-along spectator but want to give the top spot a go. Still on less than half the allowable power, just for the challenge of really optimising the overall system. IMHO winning on maximum power does not qualify for bragging rights.

    Apart from the amas (floats, outriggers), everything else is new for this build. The hull is a 24ft double surf-ski. A brushless motor will drive the prop via a set of angle grinder bevel gears. I built the lower unit from scratch out of Rhodesian Teak and Cherry wood. I used the same approach as on the Mora knife handle, i.e. glue lots of chunky wood bits together and let rip with the angle grinder and flappy disc.

    Bearings and oil-seals were selected on outer diameters that correspond to my available sizes of spade- and Forstner drill bits. That way I can "machine" all the necessary recesses on the drill press.
    The drill press also had to double as a crude lathe for turning the prop spinner and gland plug to seal the gears.


    Shafts and couplings were built up modular from ss bolts and long nuts. I got someone to machine the nuts down to whatever diameter was required to fit the various gears and bearings.

    Panels upgraded to 2x 300W panels with an MPPT controller.










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  14. #14
    Sharp Shooter

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    The surf-ski is an almost dead Carbonology Blast demo model, donated by the manufacturer.
    It is being held together by duct-tape and the spirit of ubuntu.









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  15. #15
    Sharp Shooter

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    Interesting and impressive! Thank you for sharing.
    A propeller designed to operate in water at the specific motor speed should substantially increase efficiency. V square drag at the tips of the long blade aero prop would sap power while contributing very little thrust.
    A prop from a small electric outboard motor used for bass fishing could be a good start.
    My 2c.
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