wind turbined electric powered catamaran - HELP :)

Discussion in 'Boat Design' started by nivo7, May 3, 2011.

  1. nivo7
    Joined: May 2011
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    Location: israel

    nivo7 Junior Member

    Hi guys, for the last few days I have been reading some posts on that forum and I was amazed by the knowledge that some of you have (and the experience).

    My name is Niv and I am a mechanic engineering final year student.
    and now I am working on my final project

    I am planning and designing a wind turbine elecrtic powered catamaran.
    now, its importent to say that we never learn anything about the marine engineering , so my knowledge is quite poor on this subject.

    I was googling for long time searching for some equations related to this matter.
    I have found this website http://www.catamaransite.com/catamaran_hull_dimensioning.html
    which gave me some basic information.

    I also used "terhohalme"'s excel chart "PARAMETRIC STUDY OF SAILING CATAMARANS" to get more info about what I need to do.

    I want to make it 5m long for 4 people something small and nice

    now I need more engineering information about making the right decisions like
    planning the hull right, when it will flip over, how fast will it go, what materials to use, need to do some max stress calculations and so on...

    if anyone here made an engineering project which is only about a catamaran and can send me some information it will be GREAT!

    (the wind turbine system is no problem for me I have all the information I need except the needed HP for the motors to make this boat move)

    p.s
    ----
    I am trying to design the catamaran inspired by a scorpion shape
     
  2. nivo7
    Joined: May 2011
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    nivo7 Junior Member

  3. Jeremy Harris
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    Jeremy Harris Senior Member

    If you have the wind turbine data, then you already know the maximum forces that the turbine will impose on the mast that supports it. Knowing these forces will allow you to determine the heeling and pitching moments that can be applied to the hulls and therefore the length, beam and displacement needed.

    It'll no doubt be an iterative process though, as when you change the length and displacement you will change the power requirement, which will then change the turbine size and hence loads.

    The easiest approach might be to look at some existing catamaran designs in the size range you're thinking of, work out the pitching and heeling forces that their sails can produce and then compare that to the forces from a turbine that would generate similar propulsive power to the sails.

    My gut feeling (as an aircraft design person, not a naval architect) is that the forces that a suitably sized wind turbine will exert will be lower than those from sails. When I looked at this as a concept some time ago there were two main concerns that I had. One was dealing with the gyroscopic forces (if the boat were to turn quickly precession would place some odd forces into the boat) the other was dealing with a wide wind speed range - some means of reducing blade area would be ideal, but variable pitch blades might be acceptable. The latter is a big potential problem because of the square law relationship between blade forces and wind speed.

    On a more positive note, people have successfully built wind turbine powered boats. I remember seeing video of a Redwing fitted with a large wind turbine sailing in the Solent many years ago.

    Jeremy
     
  4. nivo7
    Joined: May 2011
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    Location: israel

    nivo7 Junior Member

    from my research I can produce 2Xengine 6hp each
    I use this wind turbine (attached file)

    the problem for me is showing all the equations for the parameters that I use
    the wind turbine will be on a 1m mast and the turbine is 2.62m.
    the surface that "feels" the wind is 4.62m^2
    at max height 3m its not supose to give me a strong torque which can flip the boat over
     

    Attached Files:

  5. nivo7
    Joined: May 2011
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    Location: israel

    nivo7 Junior Member

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

    Jeremy Harris Senior Member

    OK, it looks like you haven't quite grasped some of the basic wind turbine parameters yet. The loads that the turbine will exert on the mast aren't directly a function of the swept area, or the blade area, they are a function of the blade L/D ratio at any particular operating condition. This is why variable pitch is useful; it allows the L/D to be optimised over a broader range of wind speeds, both increasing output and reducing mast loads.

    The Darrieus type VAWT that you've chosen is significantly less efficient than a horizontal axis type, plus it doesn't have any option for adjusting its operating conditions. I can't see any mast wind loading figures on this wind turbine, so you may need to contact the manufacturer to get those details.

    The swept area of 4.62m² is very small to power a big catamaran, as you may have already worked out. The turbine can only ever extract a percentage of the energy available in the wind, typically around 50% for a VAWT design like this. In, say, a 10mph wind, an area of 4.62m² will only contain about 56 watts (power in the wind is given by 0.5 x rho x A x V²). Your turbine might get half of this, so around 25 watts, not really much power, about a quarter of the power of an average rower.

    I think you need to do some basic engineering calculations first, determine what you need in terms of swept area for a given power (look up the Betz Limit, for starters) and then decide how you want to move this project forward. Starting with an unsuitable wind turbine and trying to make it fit a boat isn't going to give a good result, I believe.

    Jeremy
     
  7. nivo7
    Joined: May 2011
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    Location: israel

    nivo7 Junior Member

    thank you for the good advice, by the way the catamaran that i plan is quite small
    5 meters long only for 4 people

    where can i find the basic principles for planning the boat?
    only the boat lets leave the wind turbine for a sec, where can I get the equations for planning it right, maybe some document that include the whole proccess
     

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

    Jeremy Harris Senior Member

    A five metre catamaran capable of accommodating 4 people is going to need a fair bit of power, at a guess around 3 to 4kW or so as a minimum, far more if you want the boat to be able to tackle any sort of bad weather or currents.

    The formula for wind power I gave you above is a good starting point. If you assume 50% efficiency for your turbine (a good enough estimate for sizing purposes) you can work out how big a swept area will be needed. This will then allow you to see the size of mast needed to carry the turbine and calculate the drag loads that the turbine will exert. Knowing these figures will allow you to calculate the heeling and pitching moments that the hulls will have to take safely.

    As you're a final year engineering student I'm guessing that you are comfortable working with forces and moments. Most of the things you need are pretty straightforward to work out. For example, once you know the moments on the turbine mast you can easily calculate the hull displacement needed to provide enough buoyancy to resist them at any given position in relationship to the point of application of the moment. It's all really first year stuff - basic laws of mechanics.

    Jeremy
     
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