CARAVELINA - New JR scow minicruiser

  • 14 Jan 2021 17:02
    Reply # 9858990 on 7917477

    Here is an attempt at a split vane gear, with the vane assembly and servo blade assembly linked only by Dyneema cords .

    The vane is mounted on a horizontal platform attached to the aft face of the cabin.

    The vane linkage lines come down, outwards and back to the centreline via sheaves or Barton rings attached to the transom, and are attached to a forwards extension of the servo blade jaw, probably an M6 eyebolt.

    The servo mounting frame is rectangular, two fore and aft and two athwartships pieces joined together, with bearings (Seasure dinghy transom rudder fittings) on the athwartships pieces for the axis. The servo carrier passes up through this frame, and the tiller lines are attached to the top of it, leading out to blocks on the corners of the transom. This makes its structure strong and reliable.

    The servo carrier is at 15˚ to the vertical, giving a positive trailing effect to stabilise the steering downwind. 

    The servo blade jaw is mounted onto the servo carrier with Seasure dinghy rudder fittings, as before.

    The servo blade is able to hinge up when necessary.


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    Last modified: 14 Jan 2021 18:23 | Anonymous member
  • 14 Jan 2021 14:21
    Reply # 9858657 on 7917477

    Kris,

    Your first sketch: yes, there can be a jaw so that the blade can hinge up.

    Your second sketch: I see that you have drawn a lashing hinge, but i think it's necessary sometimes to remove the whole gear easily, leaving just the mount. I don't think the vane linkage cord can be done in the way that you have drawn. 

  • 14 Jan 2021 09:14
    Reply # 9858351 on 7917477

    David, to save some of your time and to get engaged I made some sketches. 

    Since my boat is a flat bottomed & swing keels, it is required to have the blade swinging too. What do you think about solution?

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  • 13 Jan 2021 22:24
    Reply # 9857580 on 9854404
    Anonymous wrote:

    There is another option: to leave the servo blade and carrier as they are, and mount them at the original low level (it would be easier to lead the tiller lines athwartships to turning blocks here), and extend the vane turret upwards. I think I like this better than other options.

    To split the gear in two is almost a new design of servo, because the negative feedback is applied in a different way, and the angle of the servo carrier axis is ~15˚ - 20˚ to the horizontal, not 45˚ (I could reuse the vane assembly). I should need some time to think about this.

    The boat design shows a link between the two rudders. This would need to be far enough aft not to foul the servo. 

    Interesting, how high the vane drum could be safety located above the turret, consider higher loads due to higher moment of inertia?

    Also, the oar may be extended.  

    The line between both rudders may be spanned by a block at the transom to secure the clear room for servo blade.

    Thank you, take your time.


  • 13 Jan 2021 14:47
    Reply # 9854404 on 7917477

    There is another option: to leave the servo blade and carrier as they are, and mount them at the original low level (it would be easier to lead the tiller lines athwartships to turning blocks here), and extend the vane turret upwards. I think I like this better than other options.

    To split the gear in two is almost a new design of servo, because the negative feedback is applied in a different way, and the angle of the servo carrier axis is ~15˚ - 20˚ to the horizontal, not 45˚ (I could reuse the vane assembly). I should need some time to think about this.

    The boat design shows a link between the two rudders. This would need to be far enough aft not to foul the servo. 

  • 13 Jan 2021 10:13
    Reply # 9854001 on 7917477

    David, many thanks for your reply.

    I love the HWV made by you for Waverbird. It is easy to understand,  to make at home  and sea proved.

    I made my homework and sketched the HWV into a base drawing of the astern of my boat. The astern part is huge, almost like in the XVI century caravels. So , to have the vane somewhere between the deck and main boom, the at least 500mm extension is required. Easy, but where the carrier axle should be located? At about 500mm, as in the original project, or 500mm higher, or somewhere in between? In the first case the Vane assembly would swing asides and the control lines too. Raising the axle will increase the arm, torque and forces generated which I would prefer to avoid. Compromise by putting the axle somewhere in between would reduce the unwanted effects, but where is the safe compromise?

    At what maximum angle does the self-steering gear swing sideways? 25deg as limited with a green line in the pic.15? 

    Having all this in mind, splitting the vane and carrier assembles is tempting, despite an additional mounting is required. But all dimensions and geometry would remain as originally made by you.

    The vertical tiller is located in the central cockpit and steering lines from connected rudders are lead there. 

    I need to get to the cockpit two kind of HWV lines. The tiller control cables are routed along the sides of the boat, and the course control ones I would rout across the deck.

    I think I will make the hatch in the rear cabin wall anyway- there is too much gear to be served or repaired not to have a secure access.

    P.S. I am subject of another temptation - replacing the rudder gudgeons (hinges) with lacing. 

    Wishing all the best to you

    Kris





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  • 12 Jan 2021 15:43
    Reply # 9851513 on 7917477

    Kris wrote:

    Hi David, Hi Jami,

    I'm watching all very interested projects with conversion of the Galion 22. In an older movie I've noticed a SPLIT Wind Vane the David Tyler's make. See the attached slides taken from your movie. On the recent movie from the split sail trials it looks more conventional David's construction.

    Since the boat I am building has a very tall astern cabin, the idea of splitting the Wind Vane seems to be suiting perfectly my needs. I couldn't find anything more on this subject, so could you please give me some comments and advise regarding?

    I will not have an outboard on the transom, just two rudders.

    Cheers to both of you

    Kris

     

    Kris,

    Aha, a nice design project to look at!

    If you split the vane away from the servo assembly, it adds to the complication of the design and construction. It's possible, and it would be similar in principle to the gear I designed for Tystie (but whereas Tystie has two servos and one rudder, you have two rudders and one servo.

    However, I can't immediately see how to connect and disconnect the servo from the rudders quickly and easily, since the aft cabin makes access very difficult. 

    One thought is to put a hatch into the aft cabin or transom, and open it to reach the connection, but this would be very inconvenient.

    The assembly that I made for Weaverbird, which Jami has now copied, is the easiest kind of pendulum servo gear to build, easier than splitting the vane away from the servo with a cord linkage. What I would suggest is that you follow this design, but extend both the servo blade and the servo carrier by the same amount, so that the vane sees clear wind above the aft cabin. The mounting would have to be adapted to fit onto your transom.

    Then the steering lines can be lead forward along the aft cabin top to the cockpit, where you can connect them to the tiller/whipstaff/wheel in the usual way. Because of the length, those lines had better be Dyneema. 
  • 24 Dec 2020 10:05
    Reply # 9449833 on 7917477

    Many thanks Arne and David. Now I am informed regarding this issue and able to make informed decision. If I make the boom strait, should add to the bottom of the lowest panel a foot shelve or longer sleeves, as applied in the Mingming II. If decide to treat the boom as another batten and make it hinged - the sail is simpler and the rig more unified. 

    When analyzing supplier's scope of alu pipes and playing with the geometry I came to an idea (eternal re-invented the wheel ;) ), that some flattening the outer sleeve pipe  would be quite beneficial. Would allow applying smaller pipe and better distribution of pointy pressure forces between batten and outer sleeve.

    Very merry Christmas! 


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  • 24 Dec 2020 09:12
    Reply # 9449769 on 7917477
    Anonymous member (Administrator)

    Kris,
    When I modified the flat sail of my 23’ Malena by adding hinges, back in ‘91, I kept the boom and the top batten straight. I guess my foggy idea behind keeping the boom straight was to keep a firmer base for the reefed or furled sail bundle. Anyway, that sail surely was powerful, with 10% camber in it. The lowest panel may not have looked so good. Looking at it now, I think the introduction of a taut, elastic tack line would have sorted it out.
    Look up JRA-NL 24, both the article and on the backside cover, and you will see how it looked.

    Merry Christmas and good luck with your work!
    Arne


  • 24 Dec 2020 08:43
    Reply # 9449704 on 7917477

    The way I do it is to make the "boom" as just another hinged batten, so that the sailmaking is easier. I don't know how the bottom panel would be shaped if it were straight.

    Then you arrange the topping lifts so that there is no sag in the bottom of the sail when furled, which is easy enough after a little experimentation. One leg of the lifts going to the hinge point is a good start. 

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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