gybing center boards

Discussion in 'Multihulls' started by warwick, Jul 4, 2012.

  1. brian eiland
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    brian eiland Senior Member

    While we are working on these 'definitions', I've got a question to ask. Why are we referring to 'gybing' boards??

    Gybing is a downwind sailing term, and I don't see a great need for any boards to reduce leeway when I'm gybing downwind. In fact I would just as soon 'slide' off to leeward to make that downwind mark sooner?

    So I believe we are really talking about 'tacking boards' ??

    Regardless of all the subtleties of the leeway angles, board shapes, hull shapes, etc, the fact is there are very few (if any) aircraft flying around with symmetric foiled wings...they are just not as efficient at developing lift. Lift is what we want our board(s) to develop to reduce leeway. An asymmetric board can develop more lift per unit area of board than a symmetric one.

    Correct?
     
  2. brian eiland
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    brian eiland Senior Member

    I had forgotten all the details as I was really getting into multihulls at the time. Thanks for remembering the boat's name Terrorist, I had forgotten that also ;)

    There were a number of advancements that got rated out of existance....as I point out HERE
    "years ago, I was a younger fellow aspiring to become a sailing yacht designer. I was particularly interested in ocean going, cruising boats. I would devour every reference I could find on what made sailboats work. With keen interest I followed new developments on the racing circuits, believing that this was the incubator of fresh new ideas to speed our progress across the seas. Surely this breeding ground would bring significant evolution to the sport of sailing and the art of designing.

    "Au contraire", I became disillusioned so soon. Bruce King's fantastic twin, asymmetrical, bilgeboard development, disappeared in little over a year. Prof. Jerry Milgrams cat-ketches were afforded a similar welcome. Truely different sail rig innovations were totally discouraged, and numerous other design innovations were "rated" out of existence by handicap racing rules. Ocean going boats were not being designed to "mother-ocean's rules", but rather to some arbitrary, man-created, racer/cruiser rule.

    No thanks, let me look elsewhere. A group out of England, AYRS, Amateur Yacht Research Society came to my attention. A relatively new group of multihull enthusiast and their new publication, "Multihulls Magazine", also caught my attention. Here were some sources of true experimentation, innovation, and creativity; and subsequent evolution of the art of sailing, unbridled by handicap rules. Today, look at the French and their fantastic ocean racing boats both mono- and multi-hull; exciting innovation.

    Evolution; nature's onward march to better itself by slowly rejecting less efficient characteristics of the whole, and either replacing them with more efficient offspring, and/or redefining the whole as an entity. Change comes so sloooow in traditional sailing. Look how long it took the traditionalist to adopt the fully battened mainsail that multihulls have long been exploiting for the better part of 25 years. Did they just resist acknowledging it because it was foreign to them, or was it the handicap rules. I suspect both, but there is no doubt to its superiority; ah evolution!"
     
  3. Doug Lord
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    Doug Lord Flight Ready

    =========================
    Bryan, that is just a term widely used throughout history to refer to a board that automatically changes its angle of incidence from "X" degrees on port tack to "X" degrees on stb tack and that may have a lock to prevent it "gybing" downwind. Just one of those funny things.... Changing the name at this stage is probably not helpful because some people might not have a clue what you're talking about. I've heard the term "gybing board" for over 50 years....
     
  4. brian eiland
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    brian eiland Senior Member

  5. smallyachtsailr
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    smallyachtsailr Junior Member

    I think I can answer both your points. I believe the term "gybing board" is used because like a boom, the board crosses the boat's centerline from P to S or vice versa.

    On your second point: As a closet aerodynamicist, I know that most aerobatic aircraft have fully symmetric wings, because they're often flying inverted or performing maneuvers during which they intermittently become inverted. Contrarily, most (all?) non-aerobatic planes do indeed have asymmetric airfoils.

    I'd have to do some research to give you an idea of the % difference in lift per unit area of symmetric vs asymmetric wings (for aircraft), but I don't believe it's a huge difference--I'm guessing around 10% or less--can anyone give us a better number here? Or better yet a number for symmetric vs. asymmetric sailboat boards? Surely someone has done tank tests on this.
     
  6. warwick
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    warwick Senior Member

    Hi Brian, the idea for calling them gybing centerboards came from an earlier thread.

    In hind sight I have thought it would have been better calling them tacking center boards.
    what ever prefix used could be open for confusion. Tacking and gybing are Maneuvers
    and a pivoting center board could be seen as a swing center board.

    In general the thread is open to all form of lateral resistance
     
  7. Doug Lord
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    Doug Lord Flight Ready

    -------------------------
    Bryan, its the front that moves-look closely at that sketch. Heres a rough sketch:

    click-
     

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  8. RHough
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    RHough Retro Dude

    Also like a gybe the board goes from one setting to the other automatically. It is held in the gybed position by the water flow.

    The relationship between the pivot point and the flow resembles a sail during a gybe.
     
  9. Silver Raven
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    Silver Raven Senior Member

    Gooday to you 'S-Y-S' - THANK YOU so much for - finally - bringing some overall perspective - into this discussion. I am adsolutely sure - there are many - reading all this material - that are trying to - both - learn & share ! ! ! I take my hat off to you, Sir. Thanks

    I only wish - we could afford to view a lot of the 'tank-tests' that have been done - over a long period of time. Me thinks that might cost 10's of 1000's of dollars in any currency.

    I'm very pleased that you have brought up (at least as I read what you've said) - that a boat is not a airplane - nor are wings - c/b's, keels or rudders - nor by the way is a sail(s) - directly 1 to 1 - related to a wing of an aircraft. Aero & hydro - dynamics - just don't work that way.

    Brian & Wassa - will you two - PLEASE - give us all a really big rest - PLEASE try to resist the urge to be so 'pedantic' - which destroys the flow of the conversation. To me - at least - it really just shows - that you're not helping the discussion - ie - if you've got not much of a positive advancement comment to offer -PLEASE - just sit back & stop trying to 'teach' us how smart you two are - again - to me - just comes across as you really don't have all that much long-term - wet-***, hard-knocks sailing experience.

    While it might look like 'good copy' in print to you - it really is not helping people to 'Keep It Super Simple' & get on with the learning curve - that - I thought this coversation is supposed to be all about.

    PLEASE - don't take what I'm saying in any negative way - however I've gone into many many parts of these 'forums' & most of what you to are saying - is not all that helpfull & really does lack - 'on-the-water' & 'at-the-coal-face' experience & 99% of your comments are theoritical conjecture - or at least - come across that way.

    Nothing is a short-cut for; a wet ***, cold hands, breaking gear - then re-designing it - rebuilding it & going back out to do it all over again - probably 100 times over - for more than 15 years & then - just then - thinking - golly-gosh - I (that's me not you) reference there - - I was off on the wrong tack (or gibe) - who bloody cares - NOT ME - - off-on-the-wrong-tack/gibe - - spent all that time & money & now have to go & start all over again from the begining. I'm sure you could ask a 1000 people in here to let you know - just how that feels - as I don't think I'm alone - with those experiences.

    Again - PLEASE - don't take any of this any other way than constructive comment.

    Now back on topic. There seems to be some thought - that - a 'movable cord' board - is only efficient for a short burst - period of time ??? I do not share that experience while sailing several classes on the water while in very close - tight racing conditions. I'll need some serious convincing on that one. Anyone out there that can please - show me - how it only works - sometimes - or for - a short time period ???


    Thanks everyone. I'm trying to learn - so I can build some foils - this year - I'm not trying to start an arguement or get into a 'deep & meaningful' just before dinner or sleep time. Ciao, james

    Just try to stick to the - real sailing facts - PLEASETHANK YOU, james

    'S-Y-S' - may we Please - have a lot more of your comments - as I've forgotten 99% of the studies - that you've offered to explain to us. I'n my case - it may be age related (mine not yours) Thanks, james
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    Paul B has encyclopaedic yachting knowledge, especially the IOR period, and he is correct, of course, about the overall performance of Terrorist ... but the point I was making is that in the OTC race where she won, her beating to windward was, from what I remember journalists writing and sailors saying, completely outclassing the conventional designs of the time. Maybe conditions then were perfect for the boat but whatever, the windward sailing of Terrorist was outstanding and exceptional; it made a big impression.
    And we know today that this has to be true; regard the Open 60's, VO70's etc. with their asymmetric boards helping their reaching/running, flat iron hull designs beat to windward in a superior manner than their wide hulls would normally achieve.
    A study of Camper's superior beating performance compared to the other designs would be interesting.
    Still would like to see a narrower beam, but planing lightweight hull, twin lift bilge board, internal ballast design, wing mast rig, appear.
    Ooops! - getting into Speed Dream territory.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    --------------------------------
    But, but, but you forgot DSS-geez...
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    Yes, yes, of course, quite forgot, DSS too. Now this is turning into a true porcupine of appendages.
     
  13. Paul B

    Paul B Previous Member

    There is no doubt Terrorist was fast upwind, especially in a breeze. She was first to the weather mark in the race she won, was 6th (of 33) to the top mark in the 2nd race (behind a Holland leading, a Kaufman, and Petersons), 2nd to the top mark in the 3rd race where they lost the rig (trailing a Peterson), and led to the top mark in the last race (with a couple of Petersons and a deRidder right there).

    Some of that was probably due to the bilgebaords. But I suspect a "Resolute Salmon-type" daggerboarder would have been better.


    I think the boats would be better reaching with more neutral boards. You don't need to claw to weather on a reach, and you would have less drag.

    Downwind you would actually want the lift reversed, so the board was dragging you to leeward.
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Agreed, Paul, your last couple of comments, but I was meaning (and probably didn't word it clearly enough) that the VO70's, with their hulls designed primarily for offwind and surfing work (not great hull shapes for windward sailing) but with their asymmetric boards allow them go to weather very well considering their flat iron shapes and hard chines aft and almost square, flat bilges running right to the bow.
     

  15. Silver Raven
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    Silver Raven Senior Member

    Gooday paulb & Gazza. I've a problem - understanding these things. 1st/ paulb states - something like - you don't need to claw yourself to weather on a reach - oh really - however - if one were to 'claw' onself - down the course - in the direction - of the next mark - or where one wanted to go - & be able to do so more efficiently - would that not be the desired outcome ???

    paulb states that - he thinks the boats would be better reaching with more neutral boards - O.K. but then why do the top 10 monohull & multihull designers in the world - as well as the top 300 sailors - not agree with paulb & continue to all 'get it wrong' by doing the other thing - yet again I don't understand ???

    paulb states that - & you would have less drag - O.K. - less drag than what - may I ask ???

    If the above are all correct - why is every single yacht in all classes of - big league - out & out - ocean racing monohulls & multihulls using this 'wrong' premis - to - I would have thought - go faster & more efficiently ??? Yet again I just don't understand.

    Paulb states that - downwind you would actually want the lift reversed, so the board was dragging you to leeward. That is exactly correct & is easily done by having the forward edge of the foil - slightly to windward - then the trailing edge of the foil - slightly to leeward & then continually - gently pulling the rudder to windward - lightly & slightly forcing the - bow-down & thus - the course made good - would be made much faster. This will wrok very well - only if the foils are of the correct size, shape, section - that is correctly matched to the hull(s) shape of the vessel in question.

    Pulling the bow down - slightly - away from the desired course heading - is not always - the slowest way around the course or to the next mark.

    Go & have a look at all the under-water shapes in all the top classes & - you may well see something that some may have missed before - especially those with a 'bent' to not want to see what they are truely looking at but rather - what they want to see.

    Try looking - into - rather than at - boats like - Groupama 2 or Groupama 3 or BP5 or Spindrift or a couple 100 others & - - you'll either see it or you will not.

    Gary - if I got what you are/were saying -= I can't figure why other - far smarter people - with far less handicaps than I - can't see it ???

    Paulb, Gary & everyone else - Please keep - hanging-in-here & try to teach me - cause I'm still trying to learn more & more - cause I'm building at least 3 'split-foils before the end of the year. Thanks again, james
     
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