How powerful a wind turbine do I need to recharge my electric boat?

wind turbine

How powerful a wind turbine do I need to recharge my electric boat?
I am building a two-seater, electric catamaran, 21 ft. long, about 8 knots top speed, no sails, just two electric DC engines. I am aiming at a range of about 20 miles before it needs recharging, and my only recharging device will be a wind turbine. I've seen they do about 100 - 400 Watts when they are the marine type which usually attaches to sailboats; how long would it take for such a turbine to replenish energy in my boat, would anyone know? I'm hopeless with these things, but I still love doing them.
Thanks so much!

Best answer:

Answer by mel
you'll never get it high enough to work with regularity in a boat without sinking it in a storm.

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8 Responses to How powerful a wind turbine do I need to recharge my electric boat?

  1. Greed_2.0

    Sails do not have conversion losses and are cheap.

    A 3.5Kwatt Electric Generator would work better for a battery bank.

    A wind charger will cost you more than the above. Lets say you get a full 400 watt/hour output – you will get back less than half a horse power for one hour.

  2. Heinz M

    First of all they are electric DC motors, not engines.
    Secondly, you would have to determine in how long a time you want to be able to recharge the batteries. Based on their capacity you could calculate how much power for how many hours that would take and set up the windpower generator to accomplish that.
    Next you would have to be at a place where the wind blows hard enough to generate that power.
    Unless you go for weeks before running the boat again, this is not a feasible way to get much use out of that boat.
    If you dock your boat in a creek or river feeding the lake, you might consider a water turbine, which is much more efficient than windpower.

  3. linlyons

    so what engine rating are you going to install?
    just for giggles, let’s say 2 hp.

    and how long are you going to charge it?
    1 hour?
    over night?

    1 hour, you’ll need 10k watts. (4 hp*hr at 50% efficiency.)
    over noght? 500 watts (10k/20 hr.)

    you will have to check the expected efficiency — i was just guessing.

  4. Steven B

    lol, this seems contradictory to me.

    If you are going to rely on wind power for your boat to function, why not just get a sailboat?

  5. Left_Field

    Just go ahead and build the boat. It will provide a world of experience and fun no matter how well it works. You can do a lot of calculating ahead of time, but in the end, it is all theory. Don’t let fear of failure cause you to procrastinate too long.

  6. Tom H

    If you shoot for a very efficient design, it might work OK. I wouldn’t plan on carrying the turbine with me on the boat. If you could leave it somewhere & hook-up to it when you get there, it would be more practical.

    8 knots isn’t too fast. 20 miles at 8 knots is about 2 hours transit time. Two 1/2 HP motors would work. Human powered catamarans have gone much faster than 8 knots & one man is about 1/2 HP or 375 Watts.

    If the motors and propellers are efficient, then a total of 600 Watts might do it, assuming two passengers.

    Let’s say the turbine generates 200 Watts. Then you’d have to recharge for about 6 hours.

    I’ve assumed 100% efficiency throughout. The true efficiencies are pretty high with good equipment, but not 100%; so figure 7 or 8 hours of recharging.

  7. John H

    Need more information. What is the ampacity of the Batteries?

  8. cycloneweaver.com

    Do this practical experiment
    1. build your boat
    2. Put an outboard motor on it and see approximately how much power it takes to drive it at 8 knots.
    3. With this information you have a starting point for your electric requirements. Say you need 10 hp = 14 Kw (approx) If you use old forklift motors at 48V you would need 2 x 7 Kw motors if you wanted the boat to keep on going you would need a 16Kw generator (efficiency losses!) this would take a blade of approximately 20′ in diameter that you would need to direct into the wind at all times also the gyro forces would demand that you beef up the bearings supporting all this machinery. By now you would have figured out that to go directly into the wind with this machine you would have a 16 Kw force pushing down wind and 14 Kw force pushing you up wind net result you will go backwards!

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