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A vane gear for Weaverbird

  • 19 May 2017 15:52
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    Reply # 4842113 on 4048415
    Anonymous member

    One thing I've been finding is that the vane axis must remain either horizontal, or inclined with its forward end higher at all times, or it becomes unstable. This is fine, with the vane axis horizontal and parallel to the base on which the vane turret is mounted, so long as that base remains truly horizontal. When sailing to windward or on a beam reach, the angle of heel will supply a little positive inclination. On a run, it doesn't. If the whole gear droops down aft, even if only by a little, the vane axis inclination goes negative and the stability of the steering is adversely affected. So my current thinking is to build in a little insurance by inclining the vane axis at say 2°, and then also raking the whole gear forward by 2°. This would give 4° of inclination when running, reducing to 0° when head to wind.
  • 11 May 2017 15:11
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    Reply # 4826924 on 4048415
    Anonymous member

    That's right, Arne. The inclined power axis makes the vane turret tilt so as to apply negative feedback, but only when the servo has swung over, not just the vane. This means that the gear is more powerful, yet better controlled, than the conventional servo pendulum arrangement. 
  • 11 May 2017 02:46
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    Reply # 4825516 on 4825232
    Deleted user
    Arne Kverneland wrote:

    Most elegant, David!

    It slowly dawns to me how the whole thing works and produces a bit negative feedback to prevent over-steering (those canted hinges, right?). However, it is like with the Wankel engine and Stirling engine  -  I only have a very loose idea on how they work...

    Arne

    Well, you're way ahead of me, Arne. I'm hoping for a full theory of operation description, because I'm pretty much baffled as to what we're talking about here. 
  • 10 May 2017 23:37
    Quote
    Reply # 4825232 on 4048415
    Anonymous member (Administrator)

    Most elegant, David!

    It slowly dawns to me how the whole thing works and produces a bit negative feedback to prevent over-steering (those canted hinges, right?). However, it is like with the Wankel engine and Stirling engine  -  I only have a very loose idea on how they work...

    Arne
  • 10 May 2017 10:12
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    Reply # 4823830 on 4048415
    Anonymous member

    https://goo.gl/photos/7xUQYQ2vTYhDY4rW6

    A short video of the vane gear holding a steady course on a beam reach.
  • 09 May 2017 12:53
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    Reply # 4821890 on 4048415
    Anonymous member

    Yes, I'm pleased and relieved, Peter. It's working well, if not straight out of the box, at least with only minor tweaks. The latest little tweak is to add a strop to limit the angle of the vane, as it can turn upside down if the lines are disconnected and the vane gets aback. I think this may have been the cause of one of the initial breakages. 
  • 09 May 2017 09:08
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    Reply # 4821719 on 4048415
    Anonymous member

    David

    That all sounds very positive.  You must be pleased with the results. I follow with interest.

    Peter
  • 08 May 2017 19:15
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    Reply # 4820797 on 4048415
    Anonymous member

    Three photos of the gear in action are now in my Weaverbird album - http://www.junkrigassociation.org/Sys/PublicProfile/

    2757889/PhotoAlbums/51809381
  • 07 May 2017 08:26
    Quote
    Reply # 4818758 on 4048415
    Anonymous member

    This is very encouraging. The first passage, from Ravenglass to the Fleet Isles went well, with the gear steering well on a reach. I've just weighed and sailed out on a run, the apparent wind is only just strong enough to feel, and the course keeping is very good. One liitle experiment is working, I'm glad to say. I have the course setting lines such that if they are cleated, they add in some negative feedback on tip of that inherent in the Hebridean design. For anyone used to conventional vanes on fixed base, it takes some getting used to, to see the turrent swaying to and fro, and also rotating a little at the same time. Weaverbird is quite twitchy to steer, and reacts very quickly. I don't think any other design could cope as well.
  • 03 May 2017 18:02
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    Reply # 4812590 on 4048415
    Anonymous member

    The short sail that I had last Saturday told me that the Hebridean-principle vane gear is going to work. How well, I don't know yet, because the power take-off yoke broke when I missed stays and made a sternboard, putting an unfair load on it. I've fixed it now, and altered things so that the steering ropes are attached to the servo carrier, and the yoke only serves to set the distance between the steering ropes and the power axis. 

    The other thing I've had to do is add limit stops so that the servo blade can only rotate +/- 25 degrees around its vertical axis. Again, this matters more when making a sternboard than when steering the boat.

    Anyway, I feel confident enough to set off cruising on Saturday.
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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