Closable Rigid Sail

Discussion in 'Boat Design' started by Andrea_Polimi, May 20, 2013.

  1. Andrea_Polimi
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    Andrea_Polimi Junior Member

    Hi,
    I'm trying to design for a university project a rigid sail that could be closable inside the boom.
    I came up to a system like this and I was wondering about what material could be used for the airfoils and what could be their thickness... (the cost and the obstruction are a matter!)
    (notice that they should be empty inside in order to contain the other upper profiles)
    Moreover, could, in your opinion, the system work properly?

    It consist in a package of telescopic airfoils connected, with the biggest profile, to the lower boom and, with the smaller (and higher) profile, to the upper boom...
    It, in a few words, is something like fun-shaped

    Thank you in advance!!
     

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  2. Andrea_Polimi
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    Andrea_Polimi Junior Member

    The length of the booms is 14 meters, and the angle between them is 50°
     
  3. Petros
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    Petros Senior Member

    Carbon graphite/epoxy would be the lightest and strongerst materail you can use for such a device.

    You do not really need hollow foil sections, a thin curved surface actually produces more lift and less drag than the thick curved surface. the only reason you need thickness in a wing or foil is for strength/structure. If your sail was designed as flat shell segments, like the pedals of a flower, it would take up less space when stowed.
     
  4. messabout
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    messabout Senior Member

    Back in time, 70 or 80 years, there were centerboards made in that way.
     
  5. michael pierzga
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    michael pierzga Senior Member

    The idea looks interesting. Possible for use on a motorboat as a stabilizer, role control or added power when motrorsailing

    How you would make it work on a boat is another question.

    Your only choice would be to make small models, then look for all the unforseen problems.
     
  6. Andrea_Polimi
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    Andrea_Polimi Junior Member

    We were just thinking about a way to make this system stand against the force of the wind...
    In particular we have thought to design the airfoils with a skeleton of aluminum covered by sheets of carbon fiber, with only a rib at the bottom... (the top of a airfoil could be sustained by the rib of their upper airfoil and so on)

    It could be enough? (The booms are 14 meters! We need a solid solution...)
    The total weight could be reasonable?

    What should be the thickness of the sheets of carbon fiber?
    Moreover, should be the aluminum skeleton a good solution?
    What should be, in you opinion (very approximately), the thickness of the components of the skeleton?

    p.s. The reason why we are designing this system without thin curved surfaces is because in this way we think that is possible to occupy less space (with the system closed)

    Thank you very much for your help!
     

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  7. Andrea_Polimi
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    Andrea_Polimi Junior Member

    Another important question!
    Someone please know the material used for the film that cover the wing of the BMW Oracle?
    I've only read that is a polyester film... but I need more specific details
     
  8. Petros
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    Petros Senior Member

    As I recall it is polyester film (mylar) with carbon graphite fillaments bonded into it that were oriented in the direction of the stress in the fabric. lots of loads analysis was done on it o determine the reinforcement orientation.
     
  9. hambamble
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    hambamble Junior Member

    I recon carbon foam core sandwich construction. You could add strength by filling in the floorof each segment. It will add strength and prevent twisting and sideways compression of the surfaces. They will still stack but it will add an additional 20mm or so at the bottom of each segment, but that's no big deal.

    Weight is a huge issue with this.. Any weight up high is really bad for stability due to its long moment arm. You really need to use strong light structures up here. A way around it might be to use a light framework out of say carbon or fibreglass, or timber for a prototype, and fill in the gaps with sailcloth, much like they used to make aeroplane wings from in the 1920's

    I did a similar collapsible wing sail for my thesis at university, and in my simulations, the weight of the sail of any collapsible structure would almost cancel out the benefits of having the wing sail profile. I ended up building a prototype and testing it on a laser... different to sail but the results were quite interesting.

    Just a question, if all the segments stack inside each other, how are the upper segments (that will be offset a fair way back due to stacking inside the lower segments) attach to the boom. I know there's ways to do it but wasn't sure what you had planned.

    Good Luck!
     
  10. Andrea_Polimi
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    Andrea_Polimi Junior Member

    Wonderful! Thank you very much! :)

    It was pretty difficult to find it on the internet!!
     
  11. Andrea_Polimi
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    Andrea_Polimi Junior Member

    We were thinking to connect rigidly the upper profile (the smaller one) to the upper boom and the lower one (the bigger) the lower boom...
    But, actually, probably we'll have to change the system because of the aerodynamic behavior of the profiles...
    We have to check if some profiles like these (pretty high chord length with a small thickness) can work!

    At bottom of each profile I've already thought to insert a rib... these ribs should give the structure enough strength (I hope! :) )

    How it was done instead your system?
     
  12. hambamble
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    hambamble Junior Member

    I used an entirely different approach that I am still developing. Don't really want to unleash it to the public until its fully developed.

    What thickness:chord ratio were you using. The best profiles tend to be thicker ones, like the NACA0012, with a t:c of 0.12... There is no reason it needs to have a long chord and shallow thickness (as all the benefits of a foil are lost). I would look into aircraft design theory on this. Remember that most sailors laugh at the idea of a wing sail. If you understand the theory behind it, there are huge advantages.

    How many telescoping segments are you planning on using? I remember seeing somewhere that there was a wing sail design where there were essentially lots of ribs connected by a sail on each side. The tension in the sail held the spans of cloth between ribs in shape. Think it was here: http://www.omerwingsail.com/general-information/
     

  13. hambamble
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    hambamble Junior Member

    Wait, think i was getting confused... Are you planning on having a mast and hoisting the sail up, or does it fold out like a fan?
     
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