Carbon Boom Design

Discussion in 'Sailboats' started by nemo, Nov 25, 2005.

  1. nemo
    Joined: Apr 2002
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    nemo Naval Architect

    Hi,
    I have to design a carbon boom in place of an existing alluminum boom of a 24metres sloop.
    First of all, the sources of loads are:
    -clew outhaul,
    -Mainsail,
    -Sheet,
    -Vang.
    The tough thing, as usual when talking about masts and sails, is to determine their values!
    I am thinking about using a Register's rule to calculate the force on the sails, such as Germanischer Lloyd. For the clew outhaul, the force could be obtained from the maximum working load of the existing outhaul's block. The same for the main sheet, and the max load of the hydraulic piston of the vang.
    After having obtained these values, I could arrange a finite element model to figure out a laminate schedule.
    Do you think it could work?
     
  2. the_sphincter
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    the_sphincter *

    More things to consider:
    reefing
    hydraulic vangs have been known to bend Al booms while pushing upward (usually don't think of vangs acting upwards, so just a heads up) and sheeting in the main all the way.
    If you go with max working load on the blocks (go with breaking load actually), beef it up alot. I'd get pissed if my boom went out when my block did.
    You'll also have to make sure (especially at gooseneck) that it can handle the axial and torsional force and transfer that properly to the gooseneck fitting.
    I wish you luck.
     
  3. D'ARTOIS
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    D'ARTOIS Senior Member

    Nemo, what will be the clew like - carbon on alu doesn't look like a good idea, but - of course - you know that. So of wat metrial is the mast made off?
    Of course you may use a titanium clew - what are your options?
     
  4. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Don't most serious sailmakers have a pretty good handle on this stuff? Seems to me if you know the loads on the sailcloth you should be able to calculate the rest...
     
  5. nemo
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    nemo Naval Architect

    Thanks.. sphincter, you are right, proper factors of safety have to be applied.

    D'Artois, I am not sure about mast and hardware material. All I know so far is that the owner wants a new "Park Avenue" boom, and a designer asked me to make structural calculations, but I still haven't seen the existing boom and its drawings.

    Stephen, since the boat already has a working boom, I think my approach is easier.. otherwise I should call the sailmaker and ask about loads on the sailcloth, and anyway I am not sure that's a thing any sailmaker is able to calculate..

    Talkin about materials, I am thinking about using High strenght carbon, unidirectional and +/- 45° (for the torsional load) for all the boom lenght, plus some 90° reinforcement in correspondence of vang, clew and sheet.
     
  6. D'ARTOIS
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    D'ARTOIS Senior Member

    I am doing some teste with the connection of Teflon impregnated AlMg 4,5 and 6
    in combination with carbon.
    I run an acceleration test in light acid seawater as a medium and run an electric current through the Alu piece that is encapsulated in carbon. So far no optical damage, but it needs to run a few days longer before I may see ome damage - or not.

    It is done to find out if Teflon impregnated Aluminium in combination wit carbon wil not react to each other, staying inert.
     
  7. marshmat
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    marshmat Senior Member

    I just want to say good luck finding carbon. Prepregs in particular seem to be in short supply right now, I'm having a hell of a difficult time finding a few rolls of what should be common weights.
     
  8. the_sphincter
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    the_sphincter *

    really? any idea why? I know boeing is making the new 787 out of carbon, and the new airbus has quite a bit in it. Any other reasons?
     
  9. usa2
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    usa2 Senior Member

    Boeing and Airbus are part of the reason. The US military is another reason, with the F/A-22 fighter, Predator Drone, helmets, body armour and other objects being made out of it. The Pentagon usually gets what it wants.
     
  10. marshmat
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    marshmat Senior Member

    The story I've been getting is that several years ago, a number of composite makers figured they had too much manufacturing capacity for the markets they had, and so several plants were mothballed.... then, with the surge of interest in carbon from aviation giants, boatbuilders and also carmakers, they found themselves at capacity again. Apparently the Boeing and Airbus plans to use carbon fibre in the new jets pushed the suppliers right to the edge and now there's waiting lists to get material.
     
  11. D'ARTOIS
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    D'ARTOIS Senior Member

    Not overhere.......
     
  12. nemo
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    nemo Naval Architect

    I think it's not so difficult to get enough carbon for a boom here...
    Please can we go back to the original thread, otherwise we can start another thread about carbon fibre supply..
     
  13. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Could you make the new boom as strong or dtronger than the old one?
    Wouldn't that be easiest?
    Woul'd that be too heavy?
     
  14. Karsten
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    Karsten Senior Member

    I would be extremely carefull just to use the break strength of the hardware. You multiply one safety factor by the other and end up with hughe design loads. You have the actual (unknown) sail force the fitting supplier applies his safety factor to dimension the fitting and then you use the break strength of the fitting and multiply that by another safety factor to determine the required stength of the boom. I would check the loads and make sure they look sensible.
    Using FE in composite design is a bit of a minefield if you don't have the proper software, experience and material allowables. You will be able to determine the yield in the boom and produce nice colourfull pictures but that's about all you can do with standard software. If you add 90 degree fibres it usually becomes critical in transverse microcracking of the resin. You would have to know all the allowable yields in all different directions for the different materials you use. The allowables also depend on the manufacturing method. Are you going to use hand lay-up or prepreg? I would keep my hands off this sort of job if you haven't got the proper tools and data.
     

  15. JLP
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    JLP Junior Member

    composite park avenue booms are a pain in the *** to design.
    my advice would be: concentrate the 0° fibres in the corners, that's where the bending stress will be.
    then you have flat panels between these corners, these work mainly in shear so mainly 45° fibres, but since they are probably large and without curvature, you will have local buckling issues, so you probably will have to go for sandwich in the side and top panels.
    finally, you need 90° fibres all along the boom to prevent the section from "ovalising" and probably some transverse bulkheads at vang and mainsheet position, and a longitudinal one under the clew track.

    if you need some help on this, mail me at jeremy.palmer "at" wanadoo.fr
     
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