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A vane gear for Weaverbird

  • 31 Dec 2017 12:41
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    Reply # 5653967 on 4048415
    Anonymous

    Hi David, I was following your development of the wind vane. I would also like to build a wind vane so if you make dimensioned parts drawings will you post them here?

    Regards

    Mark
  • 30 Dec 2017 21:19
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    Reply # 5653640 on 4048415
    Anonymous member

    This would be to me like winning at lottery, David. Your system seems to be in its own league if one combines the simplicity (of bulding, repairing and operating) with obviously steady and powerful steering.
  • 30 Dec 2017 21:12
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    Reply # 5653621 on 4048415
    Anonymous member

    I really meant to get around to making fully dimensioned parts drawings. If you're serious about making one, Jami, I'd better do that.
  • 30 Dec 2017 21:01
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    Reply # 5653620 on 4048415
    Anonymous member

    Clever geometry! The course setting lines exit the gear quite close to the power axis, so don't change much in length as the gear pivots. I usually cleat them, but it's not totally necessary.
  • 30 Dec 2017 20:47
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    Reply # 5653613 on 4048415
    Anonymous member

    Very, very simple and clever system this is - I think I will certainly go this way.

    What I don't understand is how the course setting works in hebridean-type system; you have to cleat the lines in order to keep the set course, right? But what happens, when the whole system tilts with the course setting lines tight? How can the system tilt at all?
  • 15 Sep 2017 18:37
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    Reply # 5262583 on 4048415
    Anonymous member

    There's another significant difference between Weaverbird's system and the Hebridean that may be related. As far as I can see from your picture you have no way of tilting the vane away from the wind. The Hebridean has a clamp specifically for this purpose. You might be able to make it out in this picture https://flic.kr/p/vMdBWr. The Hebridean's vane is never vertical.

    Of course this doesn't alter the axis of the vane so it may be irrelevant. But I'd like to understand your decision.
  • 13 Sep 2017 23:37
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    Reply # 5160683 on 5153480
    Anonymous member
    David Tyler wrote:
    The answer is simple. Build in a little bit of inclination of the vane axis. It doesn't have to be as much as on conventional servo pendulum gears, but it really ought to be there.
    A bit like mast rake. I can easily as some with a few washers on my Hebridean, but I don't seem to observe a problem so I'm not sure I'll see an effect.

    In any case I have a second reason to visit you now.
  • 13 Sep 2017 22:18
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    Reply # 5153480 on 5151281
    Anonymous member
    Richard Brooksby wrote:

    No, but the tilt effect still applies somewhat on upwind courses. John Fleming mentions this in his plans. And that it's less satisfactory downwind.

    And there we have it. Yes, it still applies, though the trigonometry gets complicated - so long as there is weather helm and so long as the boat doesn't roll to windward. If there is lee helm, it doesn't apply. I've rolled a little to windward, in light airs and a bit of a chop, and the vane has immediately gone unstable. Yes, it's less satisfactory downwind, because the Hebridean's tilt of the whole servo and vane doesn't have so much effect on the vane's true angle of inclination as it does on other points of sail.

    The answer is simple. Build in a little bit of inclination of the vane axis. It doesn't have to be as much as on conventional servo pendulum gears, but it really ought to be there.
  • 13 Sep 2017 22:00
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    Reply # 5151281 on 5147351
    Anonymous member
    David Tyler wrote:

    Richard, I think you have misunderstood.

    Very likely and thank you for taking the time to explain yourself.

    All those photos appear to show the vane axis pointing directly fore and aft.

    But you don't sail directly into the wind, do you?

    No, but the tilt effect still applies somewhat on upwind courses. John Fleming mentions this in his plans. And that it's less satisfactory downwind.

    This, in the end, is why vanes with a horizontal axis are unsatisfactory.  They will only work when they have an appreciable load to work against, so that they do not deflect too far during a roll to windward.
    Is that not provided by the pendulum and rudder damping in the water? When I crossed the North Sea with my Hebridean there was significant roll to my 20' boat from waves on the quarter, but the Hebridean kept an excellent course somehow. You can see it in my video “Trials of my Hebridean” (can't readily link while sailing sorry).

    In fact the drag of the pendulum in the water when the boat was rolled was beneficial, but that's probably another discussion.

    The Hebridean principle has one great  advantage over other servo pendulum gear geometries: that it greatly simplifies the primary linkage between vane and servo, and greatly simplifies the construction of the whole vane gear. It's true that the inclination of the power axis adds more negative feedback as the servo swings over, but all other pendulum gears do this anyway, by the way that the primary linkage is arranged relative to the power axis.

    Often with a right-angle gear or somesuch, if I understand correctly.
  • 13 Sep 2017 21:45
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    Reply # 5149948 on 5128623
    Anonymous member
    David Tyler wrote:I do know that whenever my vane gets its axis "low end forward", it gets unstable and goes to its fullest travel in either direction.

    John Fleming probably advocates a neutral helm because the angle through which the servo will swing is much smaller than for a horizontal axis pendulum, and so the ability to apply large quantities of weather helm is not there.

    Now I'm quite puzzled. The Hebridean pendulum feathers to the direction of the boat as it swings precisely because it is angled and the pivot is angled. The vane also feathers and tilts because of the pivot angle. In fact that's what I assumed you meant by “the Hebridean principle” because it's so fundamental. What stops your vertical pendulum always swinging right out? The Hebridean will always stop at an angle corresponding to the angle of the vane to the frame because the angles provide negative feedback, and so it applies a tiller angle corresponding to the vane angle (after a useful damping delay).

    I will stare harder at your pictures :)
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