On-deck Movable Ballast

Discussion in 'Stability' started by Doug Lord, Sep 15, 2005.

  1. Doug Lord

    Doug Lord Guest

    I've been tossing this around for a while: what about a 16-17' fairly high performance dinghy designed so that the skipper sits down in it like a mini 12 but with a difference: the majority of ballast would be in a"wing" between 6 and 10' long and would slide side to side either by electric power or by the crew using a "bicycle winch":leg power moves the weight(weight about 170-200 pounds). The whole wing would move side to side along with a weight sliding on it so the CG of the movable weight could get up to 8' or so from the CL of the boat.The wing would be supported by "Trapeze" wires. The wing and the crew seat would be somehow tied together so that the crew could slide aft as necessary and/or the boat would be equipped with a rudder t-foil.
    There would be a deep daggerboard(retractble) with some weight on it- and the ends of the wing would contain buoyancy pods to help prevent a permanent capsize.The hull would be fairly narrow and the wing would pivot for trailering or stowage.It would have a spinnaker...
    These are pictures of an rc model with such a system on it:


    The concept is to allow high performance without the physical requirements of most dinghies in order to open up the thrill of performance dinghy sailing to people that for whatever reason don't want to or physically can't hike or use a trapeze.
    I'd really like to hear comments...
  2. Tim B
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    Tim B Senior Member

    Interesting idea, doug.

    I can certainly see advantages for disabled sailors, but I wonder if it might be too vulnerable if people started racing them. What would be an easier setup would be a trimaran with a lump of lead that could slide across the whole beam (perhaps winched inside a cross-beam).

    Definitely food for thought,

    Tim B
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    FAST FRED Senior Member

    Take a look at racing sailing canoes.

    They use a plank thats tacked with a beefy crewmember on the end and go like stink.

    Like a scow there really single hulled catamarans , that flies a hull 100% of the time.


  4. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Very interesting. I have wondered why it's so common to pump water from side to side when it's probably faster to have a moveable tank.
  5. usa2
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    usa2 Senior Member

    because isnt most moveable ballast illegal unless it is inefficient in some way (i.e water ballast, canting keels..)
  6. Doug Lord

    Doug Lord Guest

    Movable ballast

    Tsk, tsk-too cynical! I don't know about this on a big boat though...
    And the "class rules" of this proposed boat specifically allow it.
  7. usa2
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    usa2 Senior Member

    would it have positve stability if your ballast rack and person ended up on the wrong side, and would it be able to right itself if not? Bicycle winches are notoriously slow, as the average persons legs are not able to provide a burst of power through the legs to drive winches. One of the 12 meters had bicycle winches (a swedish 12 i believe) and they got burned in tacking duels.
  8. Doug Lord

    Doug Lord Guest

    Movable on deck ballast

    Pretty much has to be self righting....
  9. Doug Lord

    Doug Lord Guest


    Julian Bethwaite is developing a "Lead Assisted Skiff" for reasons similar to mine for looking at this idea. His is supposed to be evaluated for the Paralympic Games in 2008.
    One thing I haven't mentioned is the "low down" effect: if anyone has ever sailed a 2.4 meter or any other boat where you sit low in the boat you'll know about this tendency to magnify speed. I did it on a small fast trimaran and the sensation is fantastic. The on deck system on a light fairly high powered dinghy with the crew sitting inside ought to be exhilarating -if it's not too wet.
  10. Doug Lord

    Doug Lord Guest

  11. Doug Lord

    Doug Lord Guest

    Power Ballast System

    For those interested in the model version of the on-deck movable ballast system mentioned in the first post the pictures referenced there(now dead links) are on the front page at: www.microsail.com
    Also, an experimental 18 footer utilizing a version of this concept is being designed and will be built for my personal use and testing. A "diary" of that project from conception thru to sailing is being kept here:
    X18-T ---Experimental 18'/Movable Ballast/Foiler - Boat Design Forums
  12. Poida
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    Poida Senior Member

    Have a pivoted seat at the stern with a fat lady in it and she swings the seat either way to ballast the boat.

    Just remember the boat trip is not over until the fat lady sinks.:eek:
    1 person likes this.
  13. Doug Lord

    Doug Lord Guest

    On Deck Movable Ballast

    Why bother the poor lady? She could just sit in the middle of the boat singing while the ballast moves--don't you get it?
    Hopefully, the design has been thought out well enough to allow the ballast to move , the lady to sing and still be self righting.....

  14. SamSam
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    SamSam Senior Member

    Bad puns are good! Sam
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