S2 6.7 Junk Rig Conversion

  • 17 Jul 2021 16:03
    Reply # 10757957 on 10756077

    I should learn to draw :)


    actually your drawing is very clear. Being easy to do and better looking than  most freehand (well mine anyway) should encourage its use.
  • 17 Jul 2021 08:16
    Reply # 10757423 on 6872873


    Scott,

    Boats with a spade rudder and no skeg are inherently course unstable. Your boat is, and so is Weaverbird

    A self steering gear for such boats must add the stability that is missing.

    The OGT does not do this. A trim tab does not do this.

    Both might give adequate steering with the wind forward of the beam, because then the combination of sail, hull and and rudder tends to have stable characteristics (where the hull and rudder alone do not). Neither would work off the wind sufficiently well off the wind to be worth the effort of making them. 

    An auxiliary rudder gear (the Hydrovane is a commercial example) adds stability to a certain degree, because the main rudder is fixed and acts as a skeg.

    Only a servo pendulum gear does a fully reliable job of adding the yaw damping feature that such boats need to make them course stable. And even then, I have found that unless the servo pendulum has an inclined axis so that it tends to trail and self-centre, small boats with dinghy-type spade rudders will not hold a steady course on a run. I have known this since the early 1970s, when I was working with Blondie Hasler, trying to get a Hasler SP servo pendulum gear (with vertical axis vane and horizontal axis pendulum) to work on Pilmer, his Kingfisher 20 with a balanced spade rudder.

    That is why I developed the two pendulum gears for which there are drawings in  https://junkrigassociation.org/members_files > drawings > David's vane gear drawings.

    I have to recommend that either you build one of these, or you take the easier option of installing an electric autopilot. For short passages in good weather, the latter should serve reasonably well.

    Last modified: 17 Jul 2021 08:30 | Anonymous member
  • 16 Jul 2021 16:09
    Reply # 10756077 on 10755158
    Annie wrote:

    My trim tab plus vertical vane, on FanShi, is brilliant.  And not expensive or requiring any welding skills.  Can you do.something similar?

    Annie,

    A trim tab and some sort of vane seems like the right answer.

    The problem I see, when I imagine building this, is the kick-up rudder.

    If I have a trim tab attached to the rudder in the water and the top of the trim tab stock attached up above the pivot where the rudder kicks up then something is going to bend or brake if the rudder swings up.

    Is there a simple solution to this that I don't see?

    I should learn to draw :)


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    Last modified: 16 Jul 2021 16:10 | Anonymous member
  • 16 Jul 2021 15:58
    Reply # 10756062 on 10753964
    Arne:

    Scott,

    Test 1
    you could for instance drive your boat for motor in a straight line. Then you put the engine in free and leave the tiller. If the boat starts swinging into a steeper and steeper turn, to this or that side, then it is unstable.

    Test 2 (..if the boat went straight in test 1):
    Motor into a medium steep turn, set the engine in free and let the tiller go. If the boat straightens out the course, then it is definitely course stable.

    The quicker the boat straightens up, the better is the course stability.

    Arne

    I went out to my boat right around sunset yesterday. There was almost no wind and Lake Macatawa was very calm. I think there was just one power boat that briefly threw a wake across the water.

    Test 1: The boat goes straight after I put the engine in neutral and let go of the tiller.

    Test 2: The boat never straightens up. The tiller stays more or less where it was when I let it go, until the boat has turned around and slowed down. After slowing down, the tiller moves and puts the boat into a steeper and steeper turn.

    So ... it is stable until something pushes the rudder over, I guess.

  • 16 Jul 2021 15:21
    Reply # 10755983 on 10755274
    Zane wrote:

    A man with good taste (he sails a Contessa 26) made his own version of the trimtab SS and proceeded to do an Atlantic circle.  Details per the video

    https://youtu.be/Wcd9Y5AS6qE

    Zane,

    I had not seen this one before. Thank you for sharing it. In my opinion the price he is asking for plans and videos is very reasonable so I purchased a digital copy.

    The only big issue I see with me building this design is that there is some welding required. It appears to be one very simple weld, but I do not personally have any of the equipment or skills.

    Last modified: 16 Jul 2021 15:23 | Anonymous member
  • 16 Jul 2021 09:24
    Reply # 10755274 on 6872873

    A man with good taste (he sails a Contessa 26) made his own version of the trimtab SS and proceeded to do an Atlantic circle.  Details per the video

    https://youtu.be/Wcd9Y5AS6qE

  • 16 Jul 2021 07:17
    Reply # 10755158 on 6872873

    My trim tab plus vertical vane, on FanShi, is brilliant.  And not expensive or requiring any welding skills.  Can you do.something similar?

  • 15 Jul 2021 19:50
    Reply # 10753964 on 6872873
    Anonymous member (Administrator)

    Scott,

    Test 1
    you could for instance drive your boat for motor in a straight line. Then you put the engine in free and leave the tiller. If the boat starts swinging into a steeper and steeper turn, to this or that side, then it is unstable.

    Test 2 (..if the boat went straight in test 1):
    Motor into a medium steep turn, set the engine in free and let the tiller go. If the boat straightens out the course, then it is definitely course stable.

    The quicker the boat straightens up, the better is the course stability.

    Arne

  • 15 Jul 2021 18:36
    Reply # 10753839 on 10750959
    Arne wrote:

    Scott, there is also the OGT MkI model. It is a little bigger than Mk II, and Belcher reckoned it is twice as strong as the Mk II.

    It is not easy to sit on one's armchair and say "this will work" or "this will not work", in particular with windvanes. 

    It depends on the tiller forces on your boat. My 1.4ton Malena had an unbalanced rudder so tiller forces were noticeable.  If your tiller forces are high, then I would suggest the MkI vane directly on the tiller.

    In case the boat is directionally unstable, I suggest you fit a rudder-like thing on the transom and lock it in mid-position. That will act as a skeg, and can also work as a spare rudder if needed. You may well make this before you build a wind-vane.

    Arne



    Arne,

    I am not sure how to say if my boat is directionally stable or directionally unstable. Can you suggest some experiments to help me determine the directional stability?

    I do like the idea of having a spare rudder. I expect my boat would spin in circles pivoting on the keel if somehow the rudder became separated from the hull.

  • 14 Jul 2021 16:42
    Reply # 10750959 on 6872873
    Anonymous member (Administrator)

    Scott, there is also the OGT MkI model. It is a little bigger than Mk II, and Belcher reckoned it is twice as strong as the Mk II.

    It is not easy to sit on one's armchair and say "this will work" or "this will not work", in particular with windvanes. 

    It depends on the tiller forces on your boat. My 1.4ton Malena had an unbalanced rudder so tiller forces were noticeable.  If your tiller forces are high, then I would suggest the MkI vane directly on the tiller.

    In case the boat is directionally unstable, I suggest you fit a rudder-like thing on the transom and lock it in mid-position. That will act as a skeg, and can also work as a spare rudder if needed. You may well make this before you build a wind-vane.

    Arne



    Last modified: 14 Jul 2021 16:44 | Anonymous member (Administrator)
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