self steering

Discussion in 'Multihulls' started by bill broome, Nov 14, 2008.

  1. bill broome
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    bill broome Senior Member

    any one got pics or drawings of wind-vane self steerer suitable for a 7 metre cat?

    lo-tech, hand-made, rugged, or at least pretty would be good.
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

  3. bill broome
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    bill broome Senior Member

    thanks, but...

    most of those guys have a metal fabrication shop, and spend too much time in it.

    i like the bungy cord and jib sheet style, but it doesn't work off the wind.

    so i'll build my own. if i get something that works, it'll be in living color here. may take a while though- very hard to get 'rugged' and 'sensitive' in the same 'rustic/primitive' implement...

    meanwhile, if you see something with plywood, cords and miniblocks-
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    A flap attached to stern rudder (just like in aeroplanes), small (pref aerofoiled) wing in a vertrical axel controlling the flap. Adjustment knob to turn the wing to desired position.. :D
     
  5. bill broome
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    bill broome Senior Member

    td, i have come across references to this technique, in high tech devices.

    not certain why it works, as the aim is to correct the angle between the wind and the hull. i can imagine the hull pulling the rudder towards centerline through boatspeed, and thereby causing the vane to induce a turning impulse on the fin, so on the rudder. very indirect and maybe unresponsive, especially if you lose speed quickly.

    on the other hand, fewer moving parts, not much friction- i'll try it out.
     
  6. oldsailor7
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    oldsailor7 Senior Member

    Having fiddled with all kinds of so called self steering devices over the years-----I only have one piece of advice.

    Get an Auto Helm. :cool:
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

    Bill, changed wind direction turns the wing turning the flap to the same direction, which turns the rudder to opposite direction...

    In shorthanded cruising it's more convenient to have both a windvane and an autohelm. They actually aren't compareble, other steering relatively to wind and other to a heading. Sometimes depending on the circumstances it's a huge difference
     
  8. oldsailor7
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    oldsailor7 Senior Member

    Thats a very good point, and it just depends on what you want to do. :cool:

    For instance we sailed from Sydney to Lord Howe island on auto pilot the whole way.

    The pilot held us to the most direct route. We adjusted the sails to suit as we went along.

    As the wind backed we hardened up the sails. As the wind rose we reefed.

    We ended up with a triple reefed main alone on a very close reach, with never an anxious moment. Average speed for the whole trip was 10.2 kts.

    We were sailing a Spindrift 45 Catamaran, with three crew.
     
  9. bill broome
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    bill broome Senior Member

    i am willing to believe a passive, wooden, device won't work as well as a well-fed 1st mate, but i can't feed a 1st mate so will have to aim for 'better than nothing.'

    regards, bb
     
  10. rayaldridge
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    rayaldridge Senior Member

    Bill, find a copy of John Letcher's book, Self-Steering for Sailing Craft. He devotes a lot of the book to home-made windvanes, and even shows sheet-to-tiller setups for sailing off the wind.

    Whether or not such approaches will work for you is partly determined by how fast your boat is. Fast multihulls are generally not considered good candidates for windvanes, because the apparent wind can change so much in a puff.


    Ray

    http://slidercat.com/blog/wordpress
     
  11. catsketcher
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    catsketcher Senior Member

    use Ebay

    Hello Bill

    For a 7 metre cat you would be far better served getting a small tiller pilot secondhand. Less money, less work and it will actually drive a multi.

    cheers

    Phil Thompson
     
  12. dialdan
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    dialdan Junior Member

    Hi Bill
    How about installing a trim tab on your rudder and then using a tiller pilot to drive the trim tab , they say it works a treat .
    You can even use a morse cable to connect them ,which helps to keep the tiller pilot out of the weather
    Al
     
  13. Landlubber
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    Landlubber Senior Member

    it does work to a certain degree in normal weather, it is when the going gets \rough that the full rudder is required, then the trim tabs units do bugger all, and it is then that you actually want it to work well, an extra pair of hands that does not fall asleep
     
  14. garydierking
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    garydierking Senior Member

    Searunner steering vanes

    The Jim Brown designed Searunner series of trimarans included the design for a self steering wind vane. During six years and 20,000 miles of Pacific cruising it performed beyond anything imaginable. Anything from 4 knots of wind with huge swells to surfing at 22 knots was never a problem. I never touched the wheel during all that time except to enter and leave a harbor.
    I'm not sure what the key factor in its design was.
    The large stern hung rudder (with a skeg under the hull) would respond instantly to the slightest movement of the trim tab. It never failed to fascinate me and I'd spend hours just watching it work. It was certainly the most valuable member of the crew.

    [​IMG]
     

  15. farjoe
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    farjoe Senior Member

    the hinges at the bottom of the rudder and the tab must sure create a lot turbulence in that area.

    Would such a system function for a semibalanced rudder with no skeg and the tab attached, perhaps more rigidly, to the back top of rudder and above only?

    Would you need 2 tabs for the 2 rudders of a cat?
     
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