Split junk rig construction details

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  • 12 Dec 2017 12:58
    Reply # 5625190 on 4449841

    Thank you Slieve and David and everyone else for chiming in. This is my first SJR and as a trial horse I am using my 14ft Peep Hen Hedwig which started out as a gaff headed cat boat which I converted to a flat sail junk using poly tarp. She sailed very well and I have lots of time in her so am looking forward to seeing the difference with the split rig. because she was a cat boat I am expecting some lee helm issues.

    This time I am using butyl dropcloth as the material which was suggested by D. N. Goodchild. He has some youtube videos of his use of the material. It is slightly more expensive than the poly tarp, $44 US for a 12' X 15' tarp, but should last a lot longer and I like the hand of it. Will keep you posted on the success of it's use. 

    David, thanks for posting your pictures. I especially like the fact that you used a dark thread. So much easier to see the detail of your build. You mentioned your video while sailing, any chance that you posted it?

    Cheers to all

    Glen

  • 12 Dec 2017 12:31
    Reply # 5625167 on 4449841

    Hi David,

    I looked at your photos of Little Gypsy Girl, and to my eyes, your Aerojunk rig looks really good.  Yes, I agree that the Aerojunk is perfectly symmetric, but I think an SJR made symmetric would be a little different from the Aerojunk rig in sail shape just because the Aerojunk has wishbones and the SJR has straight battens and bulging panels between these.  My guess is that their performance would be about the same if if we compare an Aerojunk and an SJR with identical external dimensions in elevation view (and same boat of course).

    Best regards

    Nils

  • 12 Dec 2017 10:58
    Reply # 5624587 on 4449841

    Slieve, thanks for the observations and also the help you gave along the way.  

    On the subject of the sling point, I put it there because there was no room to put it anywhere else due to my using a sleeve all along the yard. But during my 1st sail, I realized that there were a lot of diagonal creases from upper front to rear being caused by both the imbalance from front to rear of the sail and also being caused by the downward pull of the sheets.  

    So to counteract that, I ran a line from front to back on the yard allowing me to move the sling point further back using the line.  I also rigged up a yard peaking halyard to peak up the yard and allow the camber to develop to the designed batten rise angle and help remove those diagonal creases.  This can just about be seen in the sailing photo (3rd sail) and seemed to work quite well.  It needs to be tidied up though, and made stronger.  

    On the 2nd point, of the battens bending,  I hadn't noticed it at all while I was sailing, and I was looking for bending.  The sailing shot was a frame-grab from the GoPro video camera I was wearing on my head.  I had just released the mainsheet as I was about to capsize due to a big gust, so everything looks a bit messy.

    The GoPro has a very wide angle of view (170 degrees) and is prone to a bit of "fisheye", I checked a few other frames on the video where the power wasn't on and there appears to be some "bending" in these as well.  So maybe it's just the "fisheye" effect.  I hope that's all it is.  But maybe they are bending.  If that's the case, unfortunately for me, it's out with the wallet for bigger battens and the sewing machine again.  

    The dinghy has now been put away for the winter, so I won't know until next spring.  

    Will keep you posted as to what happens and thanks again, Slieve.  I definitely couldn't have done it without your advice and encouragement.  

    PS: while I haven't get the upwind performance I hoped for so far, (more experience and experimentation needed), the downwind is great. Very fast and stable too.  

    Regards, Dave D.  


    Last modified: 12 Dec 2017 10:59 | Anonymous member
  • 12 Dec 2017 02:58
    Reply # 5624290 on 4449841

    Hi Nils,

    the Aerojunk as seen on Oryx, Little Gypsy Girl and L Francis does precisely what you suggest. The sail is entirely symmetrical about the mast and exactly the same on either tack. The wishbone booms, battens and yards permit the sail to tack inside them to achieve what you suggest.

    All the best, David.

    Last modified: 12 Dec 2017 03:01 | Anonymous member
  • 11 Dec 2017 22:56
    Reply # 5624120 on 4449841

    Just some lines from the armchair if you allow:  I like symmetry very much, and I think that is an instinct rooted in most of us.  Most creatures are externally symmetric, and so are most man-made vehicles, aeroplanes, boats and ships and all kinds of things where there is no special reason to make them otherwise.

    The Junk Rig can never become symmetric about the mast, as the cloth has to pass by on one side of the mast, but it can perhaps serve as a good example of a device where deviation from the ideal of symmetry gives an advantage and no practical disadvantage to speak of.  The Junk Rigs where camber is obtained by individually bulging panels are very practical and powerful rigs.  My only problem with that rig is purely aesthetic – when the sail is on the weather side of the mast and the difference in air pressure over the sail makes the sailcloth wrap itself partly around the mast.  By looking at uploaded photos, it seems to me that the wrapping tendency is suppressed on most of those rigs because a) the panels are built with a low degree of balance and b) the bulging of the panel does not seem to start at the luff but behind the mast instead.

    The Split Junk Rig eliminates elegantly this wrapping problem, as the jib part and main part of the panel are finding their shape at each tack almost unaffected by the mast.  Also, the split panels work well at a greater balance than bulging panels without split.  The only remaining symmetry issue is the eccentricity of the battens relative to the mast. If you eliminate that eccentricity, the split junk rig’s sail will be fully symmetric about the mast as far up as the split goes, which might be all up.  This would require some tinkering though:  The fore and aft parts of the batten are straight and in plane with the mast axis, but the batten has to have a loop and pass around one side of the mast, or somehow the batten splits aft of the mast and runs at both sides of the mast and comes together before the mast.

    It is practical and simple to have a batten running straight and in one piece, so I doubt that eliminating the eccentricity is worthwhile to fulfil the ideal, but I just would like to mention the thought.

    Regards

    Nils


  • 11 Dec 2017 16:25
    Reply # 5623652 on 4449841

    Hi David,

    Thanks for posting the photos.

    Two observations from looking at them are -

    The sling point on the yard seems to be in line with the luff of the main panels. The result of this is that the top two panels are hanging back a little and reducing the balance in these panels. Moving the sling point aft will force the yard forward against the yard hauling parrel, which will help to peak the yard up, remove the tenancy for diagonal creasing and probably help reduce the sail twist. Increasing the downhaul tension also helps with the latter two points.

    The other point is that in the sailing photo the battens seem to be bending a lot. Are they only 19 x 1.5 mm? Flat sails with little drive might get away with bendy battens, but the forces developed in cambered sails do like much stiffer battens. My inclination would be to not use battens less than 1"/ 25mm, even on a dinghy, and on a fairly heavy dinghy to use 30+mm for stiffness. The Wayfarer is a very substantial boat and can accept quite a powerful drive.

    It's interesting to see the angled shelves on the main panels. They look good.

    Cheers, Slieve.

  • 11 Dec 2017 11:47
    Reply # 5623330 on 4449841

    Hi Arne,  

    I did just as you said below and sewed on some webbing at each end of the Jib and Main to allow me to tie the Jib and Main panels together and also to the ends of the battens,etc.  

    In my case though, I left all the jib panels completely separate from the Main (as per Amiina's current set-up) so I can adjust them back and forth a bit till I find the perfect balance. 

     Next time, I will also take your advice and leave the batten pockets a little short of the luff/leech.  This will make life easier when sewing the tabling.   

    I have finally posted some pictures in my album of the sail construction and on the boat.  Have sailed the dinghy 3 times before putting it to bed for the winter.  Made to windward and against tide in our local river but not as well as I had hoped. 

    This is down to a variety of reasons, more work needed on the sheeting system to reduce twist at the top, (I used a slight variation of "Ah-Sup's" method, featured in a previous issue of the magazine, which separates the sheeting from the twist control and means less lines in the cockpit for a small dinghy).  I haven't got it right and there's twist at the top, the top jib is luffing when the lower jib panels are pulling ok.

    Also the leading edge of the centre-board is in bits, and is so bad it needs replacing, not repairing.  I knew that before going sailing.  

    And the unfamiliarity of sailing a Junk rig along with not being used to aft main sheeting and with no cleat.  I use centre main sheeting and a cleat on my other Wayfarer.  

    But it's early days, I know what needs to be done and I'll have it all done by next spring.  Hopefully :-)

      

    Dave D. 

  • 11 Dec 2017 10:48
    Reply # 5623313 on 4449841

    Yes Glen,

    If there is no batten rise then they would be symmetrical, but with the rise included and the construction lines staying parallel to the luff then they become more asymmetric as the rise angle increases. We used only 5° rise on Amiina's latest sale and with the high sail balance it is more than adequate.

    Cheers, Slieve.

  • 11 Dec 2017 09:55
    Reply # 5623294 on 4449841
    Anonymous member (Administrator)

    David, I usually prefer to write about things I have experience in, but this time I jump in with some armchair ‘expertise’, having not made a split JR myself.

    If I were to make a SJR, I would as always construct batten pockets, both for the main section, the un-split top panel(s), and the jiblets. The top section may or may not be integral with the main section. The jiblet section would be separate.

    At the luff end of the battens of the main section, I would sew on small webbing loops, and do the same to the leech end on the jiblets.

    When rigging the sail I would thus lash the jiblets and main section together via these loops. This would allow me to do a bit initial adjustment of the width of the slot, until I (thought I) got it right.

    I guess I would prefer to have the luff of the jiblet section in line with the luff of the top section, but I bet the sail will work fine even if these end up a bit out of line. I would just make sure I had a good vertical connection between the top section and the rest of the sail at luff and leech. These will see quite some load when under way.

    Arne

     

     


    Last modified: 11 Dec 2017 10:02 | Anonymous member (Administrator)
  • 11 Dec 2017 08:58
    Reply # 5623290 on 4449841

    Hello, Glen.  Yes I found the same.  

    I think the only way the upper and lower part of the lense could be symmetrical is if you had a batten angle of zero degrees.  It's the batten angle rise which causes the assymetry, I think.  

    regards, Dave D. 


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