Onboard wave energy generators

Discussion in 'Boat Design' started by HCB66, Oct 5, 2017.

  1. HCB66
    Joined: Oct 2017
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    HCB66 Junior Member

    It might be possible to mount a ratchet or pneumatic or hydraulic type wave energy system on a boat. Floats that hang over the side would move up and down creating current.
     
  2. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Three things are required in order to generate an electrical current. They are:
    1. A magnetic field
    2. A conductor, or group of conductors, that cuts the magnetic field
    3. Relative motion between the two.

    Number three is the limiting factor for a free floating mechanism that is to be used for current generation. If one of the the first two is fixed and the other one allowed to respond to the motion of a wave, then we have the mechanism for generating current. The problem is that one of the elements must be fixed or somehow provide relative motion between the magnetic field and the conductors.

    The idea has some merit if we can make it work. All we have to do is solve the relative motion requirement. It does not matter whether we move the magnetic field or the conductor, but we can not move both.
     
  3. HCB66
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    HCB66 Junior Member

    Another way to do it might be to mount it on the deck, some kind of pendulum that would swing as the boat rocked on the water. It could power a piston pump which would drive a hydraulic motor and turn a generator.
     
  4. messabout
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    messabout Senior Member

    You could do preliminary experiments with this idea, on the cheap, by using old bicycle parts.

    Deraileur type bikes have a sprag mechanism in the rear hub. (A sprag is a set of parts that transmits work in one direction but not the opposite direction) Arrange to have the large sprocket on the hub and a smaller one that drives the generator. You are simply increasing the rotation rate of the generator with respect to the pendulum arrangement that turns the hub. It might be possible to rig two hubs such that the generator will be turned both when the pendulum rises and also when it descends.

    Mechanical arrangement is likely to be more efficient than one that utilizes hydraulic components.
     
  5. rwatson
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    rwatson Senior Member

  6. HCB66
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    HCB66 Junior Member

    I remember that boat now, really interesting. I was watching a sailing video and the boat had a gimbaled oven so things wouldn't spill. Something like that is what I'm thinking of. It would just sit there and go back and fourth generating current. The bicycle wheel is definitely a good idea too, familiar with that part.
     
  7. sigurd
    Joined: Jun 2004
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    Location: norway

    sigurd Pompuous Pangolin

    Hi, I had a large buildup of ideas off my cuff hence the long unfocused post below.
    I had a bilge pump that was wave driven (looked like a water-filled bicycle pump with a disc float). There is always a difference in motion between the boat and any small patch of sea, so that is not a problem. I would maybe look at whether a linear generator could be made to work but the ratchet idea seems to promise higher relative speeds and thus less active material (copper and magnets).
    Such a bouyant up-down wave driven generator is not particularly efficient, at least not in full size (10's or 100's of kW). Among the more efficient ones is a duck shape that gathers energy when it rotates (pitch up over a wave crest and down afterwards). It is called something with duck in the name.
    Also of interest is the danish 'bolgehovel' (wave-planer - as in the tool you plane wood or cheese with) which redirects the waves via thin curved plates into a rotational stream through a transverse tube. Both the rotation and the head contributes to driving a turbine.
    I wonder what the turbine looks like, since normal tubines only use the head.
    These are supposedly efficient, and I assume scalable. But efficiency in that context is related to kW per meter of wave front, for a boat it could mean watt per unit of effort or component stowability or whatever.

    I'm not so fond of gearing so were it me I would start by looking at the concepts that use high speed from the beginning, like the hovel, or the ones where a water column oscillates inside a tank driving an air turbine, or maybe hang a horizontal propeller under a float.
    I think that Darrieus turbines are especially good at utilising flows from varying directions - like the rotational energy in a wave maybe?
    I think Leo Lazauskas have written a paper on underwater Darrieus turbines but it's not publicly available to my knowledge.
     
    Denali.Amida.YP146 likes this.
  8. sigurd
    Joined: Jun 2004
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    sigurd Pompuous Pangolin

    If you hung a turbine from a plank off the gunwale.
    If it was a Darrieus, or a normal propeller with pitch reversal, it could turn the same way all the time.
    In Norwegian it is called "svarvande slingrelodd".
     
    Last edited: Nov 16, 2017

  9. Saildreaming
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    Location: Los Angeles

    Saildreaming New Member

    Right now I'm building a Woods Gypsy (extending it to 32 feet), but once I finish it I'm gonna get a Permanent Magnet Alternator and try to use the 1 alternator for 3 things depending on condition; wind gen, tow gen, and buoy gen. My Buoy gen idea is similar, only it uses the anchor and boat buoyancy to duplicate the effect of a Buoy Generator.

    The general concept would be to use 2 anchors at anchor, your fore anchor would be normal, but your aft anchor would be oversized by a few pounds. Instead of attaching the aft anchor to the boat itself it would run through an aft mounted pulley and back into the water with a counterweight. Wave motion rises the boat up, counterweight pulls the rope down as the wave falls, and both directions crank the alternator.... It requires a pretty high gear ratio (15:1 or more) to get up to the 240 RPMs needed for the generator in question; this on it's own isn't a big deal, since wave motion is high torq, but it DOES mean that to get anything close to 10+amps in calm anchorage conditions you'll need a sizable counterweight to apply that torq. The only real limit is your boats PPI, the weight of the anchor/counterweight, and the strength of the connections/chain.

    the biggest concern I have is that each anchorage has completely different wave heights and periods, which means getting the most out of a system like that would require a lot more than a "set and forget" setup. more likely it'll take:
    • Toothed pulley mounted on aft deck
    • Aft deck reenforcements
    • Toothed belt segment with chain on both sides
    • Oversized anchor
    • Adjustable counterweight (could be something as simple as a bag you fill with dirt/rocks)
    • Adjustable gear ratio (possibly an internal 10:1 flywheel on the pulley with the end segment exposed to open air so you can slap on removable 1:1, 2:1, 3:1 gears to the alternator mount)

    This is kind of a funny concept, because the alternator's resistance literally holds your boat's aft IN the water as the wave rises, and uses PPI as a power source. Too much counterweight and it'll sink it's *** too low in the wave, not ENOUGH counterweight and the wave motion will push the boat sideways until the counterweight is up against the pulley and no power gets generated.

    Frankly it's probably EASIER to just buy gas for a 2k, but I'm sort of nerding out on the idea that I can make it work.
     
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