A vane gear for Weaverbird

  • 20 Mar 2017 16:58
    Reply # 4678245 on 4048415
    Anonymous member (Administrator)

    'V-belt' to prevent slipping course-setting line

    Very interesting vane gear, David  -  I think I understood some of it. There is one thing it has in common with my old vane gear for Malena; that large course-setting “sheave”.

    On my gear the course-setting line had an annoying tendency to slip, either on that sheave or on the one on my ‘steering wheel sheave’ .

    After having learned to use a small-angle groove or notch on my “Easy to make tiller brake”, I have wondered if this v-groove effect could be used on the course-setting sheave as well: My idea is to simply fill the present groove with some sort of putty. Before the putty sets, I would ‘plough’ a v-groove with a wedge or pencil. The gap angle could be about 30°. When in use, the course-setting line will thus work as a v-belt and hopefully be less prone to slipping.

    Just an armchair idea.

    Arne

     

    Otto at work...


  • 20 Mar 2017 13:35
    Reply # 4677771 on 4048415

    David,

    lovely piece of work, though not completely sure how it operates, are you going to bless us with a diagram?

    One point that has always interested me is the best section for the vane,  I assume flat (as most are / were) is not that good - You have a fat leading edge - would there be a benefit from curved faces?  (A shaped piece of Styrofoam between the cloth should work?) 

    Best wishes

  • 18 Mar 2017 07:16
    Reply # 4674745 on 4674247
    Annie Hill wrote:Quite fascinating, David.  It looks very elegant and I think the idea of a sinking servo blade is sheer genius  They way they kick up can be infuriating.  Why are they generally buoyant, do you think?  Did you use something like purpleheart, or weight it?
    Why are they generally buoyant? Probably because it's easier to make them that way. It's easiest to carve a piece of wood to shape. It was always wrong, the way the Hasler servo blades were made from spruce; this was probably because they were made by R A Hamper in Fareham, who were noted for oar and spar making.

    Mine is made from solid pultruded GRP, as mentioned. The Aries blade used to be GRP, but I think they foam filled it. The Monitor's servo blade is of stainless steel, so presumably will sink.

    Last modified: 18 Mar 2017 07:57 | Anonymous member
  • 17 Mar 2017 23:21
    Reply # 4674247 on 4048415
    Quite fascinating, David.  It looks very elegant and I think the idea of a sinking servo blade is sheer genius  They way they kick up can be infuriating.  Why are they generally buoyant, do you think?  Did you use something like purpleheart, or weight it?
  • 17 Mar 2017 19:02
    Reply # 4673850 on 4048415

    David

    Your vane gear looks very interesting.  I shall be intrigued to see how sea trials go.  I will endeavour  to get my Atlantic system working and perhaps we can compare notes over the summer.

    Peter

  • 17 Mar 2017 18:16
    Reply # 4673765 on 4048415

    It's high time that I began to unveil the vane gear I've been making for Weaverbird. No, it's not going to be the Willing Griffin style of "auxiliary rudder that looks like a trim tab", after all. It's my take on the Hebridean principle of operation. I think that this principle is a genuine advance in vane gear design, but its embodiment, I thought, was in need of a lot of simplification. 


    The photo shows the gear almost complete and ready to be installed. From right to left:

    • The vane comprises a frame of carbon fibre tubes, 10mm at the sides and 6mm at the top, in a V formation to put the centre of area well away from the axis; covered with a sleeve of 92gsm ripstop polyester cloth.
    • There is an integral drum, 80mm diameter, with acetal bearings. It is mounted on a shaft of 5mm stainless steel rod.
    • The vane axis supports are mounted on a large "sheave" made of discs of plywood, so that course adjustment lines can be lead forward.
    • Primary linkage lines of 2mm Dyneema will go from the drum down to the servo blade.
    • The power axis is at 45 degrees to horizontal. I have used Seasure pintles and gudgeons for this, and the mounting for the gear will clamp onto a tube that will be fixed to the transom of Weaverbird.
    • The servo blade carrier is made from strong, stable hardwood, section 63mm x 25mm. It carries the base for the course adjustment sheave, and also the Seasure pintle and gudgeon for the axis of the servo blade. At the bottom, there is an Antal low-friction ring, which turns the 2mm Dyneema primary linkage cords from the vertical direction as they come down from the vane, to horizontal as they go out to attach to a triangular plate on top of the servo blade.
    • Not easy to see in the photo is a transverse member of pultruded GRP, to which the secondary linkage cords of 4mm Dyneema will be fastened. These will lead through blocks on the transom to a point on the back of the rudder.
    • The top part of the servo blade is another piece of strong, stable hardwood, section 63mm x 25mm. It is strong bonded and dowelled to the underwater part of the servo blade. This is assembled from solid pultruded GRP sections: 10mm diameter, rectangular 50mm x 12mm and rectangular 45mm x 6mm, all faired in together to form a foil section.
    What may not be immediately obvious from the photo is the care that I've taken to ensure that all moving parts of the gear exhibit a self-centring action, to ensure course stability:
    • The vane has a lead counterbalance weight that is heavy enough to centre the vane, even if wet with rain or spray.
    • The 45 degree angle of the power axis means that the servo blade has a strong trailing action.
    • The servo blade has neutral mass balance about its axis, so that when it swings out to one side, there is no tendency for it to rotate to a larger angle of incidence due to having its CG aft of its axis (this feature is missing in the original Hebridean).
    • The servo blade is denser than water, so that it will not tend to float up to one side or the other. 
    Last modified: 18 Mar 2017 08:12 | Anonymous member
  • 06 Jun 2016 16:36
    Reply # 4059800 on 4048415
    Deleted user

    Paul, I always thought the Cape Horn had some interesting design features.  I think it fits in David's category 4 (servo pendulum, horizontal power axis).  Do you have any thoughts as to what characteristics prevented the Cape Horn from working while you've had success with the Hebridean?  Could it have been as Slieve describes and the servo blade had forward rake?

  • 02 Jun 2016 19:57
    Reply # 4054275 on 4053914
    Slieve McGalliard wrote:

    A good analogy, David.

    I like your analysis of the various gear types. My fag packet involves an inclined power axis, as you call it, as I have experience of a CapeHorn gear that would not drive itself despite being installed by the designer. I only saw it in action for about an hour in a near flat calm, so we were motoring and drifting to get a clear water flow. The only explanation I could find for its behaviour could be that it may have had forward rake which I could not judge from on board the boat.

    Fickle things, boats.

    Cheers, Slieve.

    I had a Cap Horn gear on LC and I could never get it to work... not even with the rebuilt rudder. Now I've built a Hebridean and I'm pretty happy with it. It's fast and accurate and downwind with a quartering sea, it far out performs the autopilot even though the autopilot is fitted with a rate gyro.
  • 02 Jun 2016 17:19
    Reply # 4053914 on 4048415

    A good analogy, David.

    Amiina actually has a fin and skeg arrangement, but it will not produce much damping for self steering. It's interesting that the Splinter 21 'Whisper' which Edwards sails against for PBO has a spade rudder, which may explain why it tacks so quickly.

    A friend of mine bought a FolkDancer and built a Belcher servo pendulum gear when I sent him a copy of the book. He did one and a half Atlantic circuits before being rolled in the Biscay and the boat becoming an insurance write off. He replaced it with a Rival 32 and fitted a WindPilot as he was short of time, but he always reckoned he was happier with the Belcher gear. I suppose it was easier to repair, if needed.

    I like your analysis of the various gear types. My fag packet involves an inclined power axis, as you call it, as I have experience of a CapeHorn gear that would not drive itself despite being installed by the designer. I only saw it in action for about an hour in a near flat calm, so we were motoring and drifting to get a clear water flow. The only explanation I could find for its behaviour could be that it may have had forward rake which I could not judge from on board the boat.

    Fickle things, boats.

    Cheers, Slieve.


  • 02 Jun 2016 14:12
    Reply # 4053495 on 4048415

    Ah, that might explain it - a long thin boat is not so inclined to yaw. Think of a Greenland kayak.

    But the Splinter 21 and the Duette 23 have virtually no yaw damping of their own. In increasing order of adding yaw damping with a vane gear:

    1. Horizontal axis vane direct to tiller - no yaw damping at all.
    2. Trim tab on the main rudder - not very effective, but can be OK on a heavy, long keeled boat.
    3. Fixed main rudder with an auxiliary rudder - better, and good enough for many modern boats, as demonstrated by the Hydrovane.
    4. Servo pendulum with horizontal power axis - better still. Common examples are Aries, Monitor, Fleming.
    5. Servo pendulum with inclined power axis - the only commercial example I know is the Windpilot. Tystie's gear has the power axis at 30 degrees to horizontal, and can be driven quite hard downwind. Fantail's gear has the power axis at 45 degrees, but it can be difficult to devise a linkage for that angle.
    6. Servo "gate" with vertical power axis (actually, 4, 5 and 6 form a continuum) - best of all but really too much yaw damping for most boats; the arc of servo movement is quite small, as well. 
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