Swing keels?

Discussion in 'Sailboats' started by Kevin H., Sep 3, 2004.

  1. Kevin H.
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    Kevin H. Junior Member

    (Forgive a noob...)

    I was just reading the Mari-Cha IV website (impressive boat) and in the specs it mentions a "swing keel". Umm... what exactly is a swing keel? What does it do? (And don't tell me it "swings" :p )

    Thanks
     
  2. redcoopers
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    redcoopers Member

    It "swings"...

    Actually, that's a really good description of how it works. Swing keels are made with a large bulb on the bottom of it which holds a huge amount of weight. As the boat heels (let's say to port), a non-swing keel will provide a righting moment because the bottom of the keel will rotate with the boat to starboard. However, a swing keel is set up so that it can pivot about the longitudinal axis.

    Again, if we're heeling over to port, the top of a swing keel will extend through the hull. If you push the top of the keel to port, the bulb on the keel will move even more to starboard and provide a __HUGE__ righting moment.

    Hope this helps a little. Does someone on the forum have pictures of a swing keel? This would probably be better than a verbal explanation.
    -Jon
     
  3. ErikG
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    ErikG Senior Member

  4. Tim B
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    Tim B Senior Member

    That's not meant to happen is it? - Note requires quicktime to play movie

    Tim B
     
  5. redcoopers
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    redcoopers Member

    A "poor-man's" swing keel... why, what's wrong???

    Yeah, he can just put an actuator on the bolts so that it swings to windward. ;)

    -Jon
     
  6. Kevin H.
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    Kevin H. Junior Member

    Ok, I'm gettin' it now.

    So, are these systems automatically activated? Or is there some kind of gyro system to move them one way or the other? And what moves the mass? I'm guessing hydraulics...
     
  7. mistral
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    mistral Senior Member

    Isn'it called "canting keel"???; is it the same???
    oh my poor english......
    great movie...sailboat owner's nightmare ......
    mistral
     
  8. Kevin H.
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    Kevin H. Junior Member

    There's a picture on page 28 of this month's issue of SAIL (september) of a boat Genuine Risk racing with it's keel pushed out to one side. Very interesting... I'd definitely be curious to see how this works.
     
  9. Doug Lord

    Doug Lord Guest

    Canting Keels

    Having been active in sailing and design since the 60's I have to start with a pet peeve of mine: many writers have called canting keels "swing keels" BUT in the 70's there was a great burst of development of small keelboats advertised as having swing keels. A swing keel is one where the keel pivots simalarly to a centerboard in a dinghy and is usually retracted by a hand winch. Since the entire industry and many participants used the term "swing keel" to define that type of keel so long ago I (and many others) consider that the valid definition is: a swing keel is one that pivots aft from the vertical like a centerboard but heavier. Geez, now thats out of the way,right?!
    What some "revisionists" today MEAN by a swing keel is one that swings or CANTS athwhartship(side to side). In other words a CANTING KEEL.
    Canting keels are a fin or strut that is attached to a bulb via a watertite bearing in the hull. Some small canting keels are moved by hand(block and tackle); most are moved hydraulically.A canting keel can provide a given length boat with the same Righting Moment(RM) for 40 to 50% less displacement or the same displacement for subtantially more sail area. In most incarnations of a canting keel the weight is reduced for about the same sail area(more in SA light air).
    But canting keels cannot be considered by themselves: when the keel cants to the side it develops loads more RM but it fails to develop the required lateral resistance. On Mari Cha the design also uses water ballast for upwind work where they lock the canting keel-unlocking it off the wind. So on Mari Cha and on at least one other boat the canting keel is used primarily off the wind.
    Most canting keel boats use the cant facillity off the wind AND upwind which means they MUST have some other form of lateral resistance in addition to the fin or strut that supports the bulb because when canting the keel upwind the effective area of the fin is drastically reduced by the angle of the fin. The solutions to this problem are as follows:
    1)At least one boat has been built(Atomic in Sydney ) using ACC type wings that are there specifically to generate lateral resistance when the keel cants.
    2)kFOIL- a new system that uses wings similar to the ones above but retracts them inside the bulb when they are not needed offwind to reduce wetted surface.
    3) A single daggerboard(gybing or not) forward or aft of the canting keel which can be retracted offwind.Or twin asymetrical daggerboards as used on Open 60 monohulls.
    4) CBTF(Canting Ballast Twin Foil)-this is perhaps the highest performance of the LATERAL RESISTANCE SOLUTIONS for use with a canting keel: the boat is designed so that the canting keel is comprised of a strut and a bulb with the strut designed NOT to develop lateral resistance resulting in a low drag thicker section than"normal". This is possible because the lateral rsistance for the boat is developed thru twin fore and aft foils that also serve to steer the boat. Upwind these twin foils turn in opposite directions to steer and in the SAME direction to develop lateral resistance.This is called "collective" and allows the hull and canting keel strut to move straight thru the water as opposed to crabbing sideways like most other boats do: "collective" virtually eliminates leeway. Boats using this system include the Schock 40, the two maxZ86's, Genuine Risk and many others.
    High performance canting keels cant as far as 55 degrees to each side producing enormous righting moment.
     
    Last edited by a moderator: Sep 5, 2004
  10. David W.

    David W. Guest

    Boat builder

    Just like a centerboard except it is made of a heavy material like steel plate or maybe welded up to a given shape and poured full of lead.
     
  11. Doug Lord

    Doug Lord Guest

    Swing Keel/ Canting Keel

    Just to reiterate from my previous post: some writers are calling the keels on Mari Cha,Genuine Risk, Morning Glory ,Pyewackett and the Schock 40's "swing keels" when in fact they are canting keels. This is based on the two decade (or more) old definition of a swing keel as being a ballasted keel acting like a centerboard fully or partially retracting by SWINGING aft.
     

  12. Kevin H.
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    Kevin H. Junior Member

    Gotcha'. I'll remember the distinction in the future. :)
     
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