Bridgedeck centreboard why don't they work???

Discussion in 'Multihulls' started by valery gaulin, Jan 10, 2017.

  1. Doug Lord
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    Doug Lord Flight Ready

    Arrow cat

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    As far as I know that wasn't a kick-up foil. Interestingly, the boat had kick-up rudders with no foils! Think about that.......
     
  2. redreuben
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    redreuben redreuben

    Supplementary questions. :D

    Heavy objects like batteries, fuel, water, beer etc; Is it not better to have them in the hulls assuming even distribution than in a nacelle ?

    What are the pluses and minuses ?

    Load distribution, would a nacelle actually help with mast and forestay loads ? I just assumed they would as its a deeper structure ?
     
  3. Doug Lord
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    Doug Lord Flight Ready

    nacelle

    Definitely helps with the loads-that's why all the AC cats have them:

    [​IMG]


    [​IMG]
     
  4. redreuben
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    redreuben redreuben

    What about where the weight goes ? Should a nacelle be light storage or heavy ?

    The clear advantage is isolating dangerous storage like fuel and gas.
     
  5. redreuben
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    redreuben redreuben

    Ok more questions, my interest is in cats in the 7-8m range.
    Do you think there is a wet deck height where the effect of a nacelle is negligible and a height where it is going to be a major hindrance ?
     
  6. brian eiland
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    brian eiland Senior Member

    I think you are looking at this material a little differently than one should. Sure in long planks it is not rigid.
    But in blocks etc it is a very incompressible, strong material, that has very good wear capabilities and can be self lubricating to a degree.

    Here are a few quotes:
    You can find many more positive attributes with an internet search.

    I'm not sure of which item you are speaking of constructing here?

    As I mention above I had hopes of utilizing a simple 'plain' bearing, ...but there may well be other candidates

    As I said before the central nacelle was not going to be constructed simply to support this central board(s) idea, but rather as a backbone to the catamaran fore-to-aft rigidity, and as a potential wave splitter up front, and as possible even the longeron for the headsay (no forebeam) , ala Gunboat
     
  7. DennisRB
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    DennisRB Senior Member

    One large foil is more efficient than 2 smaller ones. This is an aerodynamic fact. Less tip losses. 2 regular daggers have 2 sets of tip loss. The center mounted version only has one tip loss which would offset the lack of endplate to some degree.
     
  8. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Bridgedeck Centerboard

    I know model testing and the results obtained from it are anathema to some around here but in some recent European RC multihull races a cat with a single bridgedeck foil and a single center foil on a square platform has beaten all "normal" cats and tri's........
     
  9. UpOnStands
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    UpOnStands Senior Member

    models are fine, of cruisers.
     
  10. UpOnStands
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    UpOnStands Senior Member

    sorry but that type of bearing is designed to accept heavy vertical loads directly over the center of rotation. Look at the center of the bearing -- a simple mushroomed rivet holds everything together. bigger and heavier versions? sure but how much additional weight is acceptable to you?

    I actually used such a bearing for my son's 180kg motorbike -- made it possible to drive the bike straight into a tight space and then spin it around by lifting under the motor. But, even slight off-center loads created large wobble as the bearing is just not designed to take off-axis loads.
     
  11. brian eiland
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    brian eiland Senior Member

    This 'central board' right under the CE of the sailing rig, and central to the center of the vessel, could make for a quicker tacking vessel, particularly those cruising types that usually keep both hulls in the water at all times. :idea::D
     
  12. DennisRB
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    DennisRB Senior Member

    Another benefit. As Oldsailor said his tri tacked much better with the central fin compared to 2 outboard boards. Moving the CE of the board aft by pivoting it will also reduce the tendency to broach in a following sea.

    There are many benefits to this idea.
     
  13. UpOnStands
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    UpOnStands Senior Member

    this suggests possible implementation
    yellow is UHMW
    4 cm dia hole thru the stub arm is not shown :mad:
     

    Attached Files:

  14. brian eiland
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    brian eiland Senior Member

    You are pretty handy with those computer generated illustrations. Wish I could do it,... just never took the time to learn this new technology
     

  15. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    I was trying to look up 'surplus helicopter blades' but is was getting annoying. I know there have to be MANY out there, and likely in decent shape for our use,...just not certifiable for flying any more.

    I saw this,..oops file size exceeded forum limits

    How about this..
    http://www.nwhelicopters.com/nwh/
    (files with photos within are too large)

    How about this...
    images for helicopter blades shape
    or this...
    http://aviation.stackexchange.com/questions/8914/why-dont-helicopter-blades-look-like-other-propellers
     
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