Wind or wave propulsion of raft with irregural hull shape

Discussion in 'Boat Design' started by Katti, Feb 19, 2018.

  1. Katti
    Joined: Feb 2018
    Posts: 10
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    Location: Finland

    Katti Junior Member

    I keep landing on these forums when I'm looking up things, so I thought I might as well make a thread of my own and maybe some of you geniuses will have some fresh ideas.

    What I'm trying to do is design a propulsion method for a raft that doesn't have any kind of hydrodynamic shape or centerboard, it's essentially a floating island made of junk. For design purposes, let's think of it as an ovoid shaped raft 30 feet long with an irregular bottom shape. It is also quite flexible rather than rigid, which somewhat limits what kind of things can be built on it. The only criteria are that the energy should be freely available (so no engines), it should be something I can build myself and the raft should be able to move or tack upwind at least to some extent.

    Here's a picture of the raft roughly as it is now, though the intention is that it will be a lot bigger.

    My ideas so far:

    Wave power
    -The thing floats, so any wave action that moves it up and down will create an energy potential compared to the bottom of the wave under water. A flap or hydrofoil submerged deep enough can be used to create thrust in any direction, essentially eliminating the need for any other steering apparatus. The downside is that this isn't perhaps the easiest thing to build. I also don't know how much wave action would be required to move the raft and at what the size limitations are. I think it is likely that wind would push the raft harder than the wave-energy could propel it. Wave conditions are also highly variable, so it might be hard to construct a kind of system that can utilize it in every situation.
    What I've been thinking of is something similar to this but a lot bigger.

    Wind power
    -the problem with sails is the hull shape, or lack thereof. Several mini-keels or guaras could be deployed all around the raft, but I'm unsure how much would be needed when sailing close-hauled so that the lift generated by the sails will compensate for leeway. It might simply not be possible with a hull that has so much displacement and so little shape. This failure is a good example of the problems I face.
    -I've also looked into rotors. A wind turbine of the Savonius or Lesh type can double as a Flettner rotor, but the question is how much wind is needed and if that's realistic for practical application. Supposedly a wind turbine-rotor can provide three times the power of a sail of similar size.
    Like with any windmill ship, the breaking of the turbine while out at sea would be a potentially dangerous situation since you can't necessarily keep a spare with you or do repairs while at sea, though the same could be said for wave propulsion.

    Feedback greatly appreciated!
  2. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    Like you say, too much windage and drag but as long as you are headed in the winds or tides direction, you will be great! ))
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    An ambitious project, though possibly too much so. Wind can be used to motivate your raft, though it doesn't necessarily have to drive sails. Excess employment of wind can offer other things too, such as pumping water, irrigation, etc., so consider the options you have available, before you get married to a basic propulsion system. There's also solar to consider as well, with similar benefits. Wave energy is possible though likely not particularly practical in this application.

    Redundancy is a necessary evil, when working though as complex a set of issues as this has, so multiple options, likely for everything is also probable. Working though the various possibilities on something like this, could take a life time of head scratching and a lot of cash too.
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    " while out at sea would be a potentially dangerous situation"

    C'mon - you aren't going to sea in THAT.

    The best you can do is build yourself a Tugboat, and tow the thing around in calm weather.
  5. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    Nice bit of flotsam. Make sure you fully comply with the Collision Regulations & include a radar reflector so ships can see you.
    Last edited: Feb 21, 2018

  6. Katti
    Joined: Feb 2018
    Posts: 10
    Likes: 0, Points: 1
    Location: Finland

    Katti Junior Member

    I have little bit of solar for irrigation already. I'm pretty sure solar wouldn't be enough for propulsion even if I covered the entire thing with solar panels. I realize that it might be necessary to use several different methods of propulsion, but I'm trying to decide which ones can be ruled out entirely and which ones are worth pursuing. Wind turbines seem most promising at this point, but I'm also going to do some miniature testing with wave power to determine if it's worth investigating further.

    Will do :)
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