Onboard Video - Hydrofoil Trimaran Broomstick

Discussion in 'Multihulls' started by Doug Halsey, Dec 28, 2011.

  1. Doug Halsey
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    Doug Halsey Senior Member

    Courage ?

    Thanks Gary, but I don't really consider that what I'm doing takes much courage. I'm sailing in a 2-mile diameter lake with no sharks or alligators. And nothing like the conditions you have to be prepared for.

    Sid looks real interesting ! I'm looking forward to seeing pictures of it on its foils.
     
  2. BPL
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    BPL Senior Member

    Great video. Worked perfectly for me as well.
     
  3. Dragonpoint
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    Dragonpoint Junior Member

    Being an Aero Engineer , might I interest you in a rigid form monohull which can hold from yawing to leeward in a reach , or broad reach ? marksteele1@gmx.com Canada
     
  4. Doug Halsey
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    Doug Halsey Senior Member

    I'm not sure what any of that means, but I'd be glad to take a look.
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Hollywooding, just joking, great stuff Doug. Would that the other Doug .... instead of model toys on blue plastic??
    I had to increase float size on Frog because of burying. Sailing where angels fear to tread with no floats, just foils? Brave or crazy?
     
  6. UpOnStands
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    UpOnStands Senior Member

    Great work Doug, very impressive that so little can go so fast. Video works perfectly for me.
    My suggestion would be to double the chord of the outboard foil up by the attachment mount with maybe 50% increase in thickness and blend both chord and thickness down to the original foil at half way down the leg. Give the foil more buoyancy and positive lift and take off and when heeled w/o the drag of the ama.
     
  7. Marmoset
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    Marmoset Senior Member

    very cool! whats going on in back of boat? rudder, foil? ect......



    Barry
     
  8. alan craig
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    alan craig Senior Member

    I found the video very interesting, and no need for music anyway. Why do the foils crash so suddenly and completely? I assume this is a known problem with surface piercing foils.
     
  9. Doug Halsey
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    Doug Halsey Senior Member

    I've had a few different aft foils (all T-foils). The 1st one was just an add-on to an existing kick-up rudder. That one was hard to adjust & wouldn't stay in position. Also not deep enough.

    I don't have a photo showing the most recent one on the boat, but here it is during construction.

    It's a pretty conventional wood & glass T-foil, but very deep, and with a (crude) screw mechanism to control the incidence via the tiller extensions.
     
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  10. Doug Halsey
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    Doug Halsey Senior Member

    No, this is not a common problem with surface-piercing foils in general, or this one in particular. In something like 50 different days that I sailed Broomstick (not counting times without the foils), I experienced what I called "mini-crashes" in the video only a small number of times. (Maybe only on one particular day? I'm not sure.)

    I think the cause was a combination of the low torsional stiffness of the crossbeam assembly, combined with insufficiently tightened waterstays, mainfoil incidence set at lower-than-normal values, and more scratches on the foil surfaces than usual.

    I only included them in the video because I was highlighting the silly things that happened, not because they were typical.

    There are many more discussions of Broomstick's strengths & weaknesses on the BoatDesignList. Just search for "Broomstick". This one in particular focuses on some of its weaknesses: Foil Cavitation at Lower Speeds Than Expected https://www.boatdesign.net/threads/foil-cavitation-at-lower-speeds-than-expected.53927/
     
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  11. alan craig
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    alan craig Senior Member

    Doug, thanks for that explanation.
     
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