SJR for Serendipity

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  • 18 Jul 2019 14:07
    Reply # 7785548 on 7777985
    Anonymous member (Administrator)

    Graeme, now it works!

  • 18 Jul 2019 09:26
    Reply # 7785295 on 7777985

    Ah thanks Arne I thought that's what I had done.

    I'll do it again.

  • 18 Jul 2019 09:21
    Reply # 7785279 on 7777985
    Anonymous member (Administrator)

    Graeme,
    it doesn’t work for me either.

    There is a special procedure one must follow to make it work.

    ·         Make your posting ready but without the link, yet.

    ·         Open the JRA site on Members Area in a second window.

    ·         Find your way to your album via Directories – Membership list – and open your profile there.

    ·         Go to your wanted album and right-click and choose COPY on the diagram or photo you want to show.

    ·         Now you can go back to your posting window and insert that link there.

     

    Hope that makes sense

     

    Arne


  • 18 Jul 2019 09:07
    Reply # 7785276 on 7777985

    Anthony, the link works for me.

    Anyway I just emailed it to you as an attachment. 

    Also I just looked at your photos of Buffy - lovely little boat and a very interesting version of the SJR. Can I prevail on you to do a write-up for the magazine, or forum? There is a growing number of little boats with split junk rig now - it would be great to know how your's performs.

    Last modified: 18 Jul 2019 09:58 | Anonymous member
  • 18 Jul 2019 06:14
    Reply # 7785229 on 7777985

    Hi Graeme - I can't get the link to work; any chance if having a look at it?  It sounds like just what I need for Buffy.

    Anthony

    Last modified: 18 Jul 2019 06:14 | Anonymous member
  • 16 Jul 2019 23:22
    Reply # 7783178 on 7777985

    Thanks, and good spotting Scott. Sufficient room for the downhaul spans when reefing was something I had initially overlooked. Luckily on this little boat the cabin top/deck is open at the rear of the mast - effectively just like a dinghy - so I was able to locate the turning blocks for the spanned parrel/downhalls below deck - in fact I placed them at the heel of the mast, giving lots of drift. Luckily it works - and very well, I might say (though I have no experience to compare with conventional batten parrels.)

    I made my spans/parrels out of very light dyneema, low friction and terminating in a release clip from the bottom loop. From the release clip down to the turning block and up to the jamb cleat in the cockpit, is larger diameter softer rope. The release clip allows for quick disassembly, as this is a trailer boat. (And by lucky chance, it also prevents the loop from un-reeving when the downhaul is let go - see explanation below.)

    What I especially like about the spanned parrel/downhaul system is that it can be made so that the parrels let go immediately the halyard is released - but can not unreeve very far - the result being that when the halyard is re-made fast, the required "tweak" can be left until convenient as they temporarily still loosely perform the function of batten parrels - the tweak just straightens out the luff and brings things into better shape. Slieve's "magic ingredient."

    [For dinghy sailers: based on Slieve's diagram, this illustrates the small modification which allows quick disassembly. The spanned parrels stay with the bundle, the unclipped downhaul stays with the boat. The bundle is thus separated quickly from the mast. By lucky chance this set-up also prevents the lower loop from unreeving too much when reefing, so the batten parrel function is never entirely lost (the release clip won't fit through the D-saddle).]

    Its good you pointed out this requirement for half panel clearance minimum below the boom - actually a little more might be better. My two big mistakes, initially, were to fail to understand the need at the masthead for sufficient halyard drift - and below the boom for spanned downhaul drift. Evidently, both necessary for the SJR if it is to swing freely and work properly.

    Last modified: 18 Jul 2019 09:36 | Anonymous member
  • 16 Jul 2019 15:51
    Reply # 7782387 on 7777985

    Graeme,

    The rig looks great - and your write up is excellent.

    Question:  it looks as if the boom is less than 1/2 the panel height above the deck.  Is that right, and if so, how'd you do that and still get the spanned downhauls to work?  Or did you not use them? 

  • 14 Jul 2019 23:32
    Reply # 7779292 on 7777985

    Thanks Dave and Robert W.

    Robert S.: Yes, laying the sail cloth over a 3-d pattern ("dummy") means the result is an accurate fit, and the panels made that way are identical. Apart from overnight gluing, it was quicker to make the plywood dummy than it would have been to loft, baste and sew a single cloth panel, so, for multiple identical panels I thought it was worth to make the 3-d pattern. Slieve felt that it was not worth it and I guess more experienced sail makers would agree with him.  However it made the job straight forward for me and I will do it again when I make a bigger sail for a bigger boat I am building. One thing I do know is that the two poorly-setting jib panels do not need to be re-cut, as they are certainly all identical to each other and to the dummy.

    The following will be tedious I am afraid, but might be of interest to someone who is interested in SJR and has not yet made a sail.

    I followed the same procedure as James G (River rat), made each panel separately and did not sew them together. I layed the panels out and stapled them to half-battens which were then fastened together with screws, sandwiching the sail. It was quick to do and is quick to disassemble - however to adjust the panel along the batten is impossible after the batten is assembled. This method of fixing, which was not intended to be permanent, is probably what caused the two jibs to set poorly. If so, this same method will also provide an easy fix, when I get around to it. (However, I am not entirely satisfied with the method and think now it might be better to sew the sail together properly and either add batten pockets for (lighter) aluminium battens - or use the eyelet/ lacing method which Paul T used on Pango, which would be suitable for bamboo battens. Either of these methods will be lighter, more durable and will allow for adjustment of the panels along the battens which, evidently, can be necessary sometimes.)

    When the sail was raised for the first time (on land) I had to spend quite a while making adjustments to the attachment points of the parrel/downhauls. This business is specific to the slit junk rig. The jib panels are of slightly stiffer (brand new) cloth and by their very shape and nature would not lift and show any indication of how they would set. The main panels however were of very light old spinnaker cloth and would show easily if there were diagonal creases - so I tuned up the rig by looking at the mains panels and ignored the jibs.


    The left hand photo shows first hoist: clear diagonal creases on the mains and over-tight leach. The jibs don't really give any indication of how they are setting.

    On the right (after considerable minute fiddling with the parrel/downhaul fix-points) - the sagging mains showing nice semi-circular creases. Again, no information from looking at the jibs.

    The jib panels are stiffer, smaller and baggier, and I never saw them inflate properly until I got out of the creek and into a bit of wind. More "messing about" will now be necessary.

    Robert S: Even the mains panels proved to be very sensitive to for-and-aft positioning of the battens. Yes, sheeting angle of the jibs is evidently affected quite a lot by how much of, and how the foot and head of a jib panel is sandwiched between the battens - and also a little bit of adjustment along the batten might help- it doesn't seem to take much! I don't want to alter the parrel/downhaul fix-points any more because the mains panels tell me they are now pretty much dead right. An afterthought: I wonder if harmony between the mains and the jibs, panel by panel, is going to prove to be a point of difficulty in the making of SJR sails. No-one seems to have reported any difficulties so far, but this is perhaps the one aspect that might make the SJ rig a little more difficult to make than a conventional type. Evidently the SJR needs to be a bit more accurately made.

    And yes, you are right, there is a centre seam down the main panels. It is a straight seam (beautifully straight!) I did not put it there. I cut up an old spinnaker to make these panels and the seam was already there. It is not a tapered seam and has no effect on the shape of the panel. By the way, that light, used spinnaker cloth inflates in the slightest puff of wind and also was very easy to work with - I would have said it was the ideal material for a small junk sail. However I was sorry afterwards to have cut up a tolerably good spinnaker when I found I could have sold it for more than it would have cost me to buy some "shorts" of new spinnaker cloth. I went to a couple of sailmakers here in Auckland and found they were interested, helpful and willing to go through their rack of "shorts" and let me have some cloth at a very reasonable price.

    PS Robert W: note the position of the masthead in relation to yard. Although the halyard is not quite chock-a-block and in theory there is enough halyard drift - I can tell you for sure, it was not really satisfactory and I subsequently jacked the mast up eight inches. Actually, I would like to jack it up even further. Have a look at this photo which shows the halyard drift given by two experienced developers of low-yard-angle junk rigs. More than necessary for us perhaps: there are other factors involved with the very low-balanced soft wing sail - and I believe Amiina has retained her mast from the old, slightly taller rig. Still, you get the idea.... more is better .... perhaps especially in the case of the highly balanced (or more to the point, low imbalanced) split junk rig which has very light sheet loading and needs to be able to rotate as freely as possible.

    Last modified: 18 Jul 2019 09:41 | Anonymous member
  • 14 Jul 2019 16:02
    Reply # 7778825 on 7777985

    Hi Graeme--Looks like your 3D moulding method for creating camber works. The set of the main panels looks good.

    Re: jiblet crease(s). The aspect ratio of your jiblets looks to be greater than one. I speculate that therefore the jiblets are more sensitive (than lower aspect ratio) to crease formation from even slight relative fore-aft movement between battens. The 3rd batten from the top seems to move too far forward. Not sure what you can do. Tighten up the sheeting to that batten? Adjust the batten parrel to move that batten aft 5-10cm?

    On the plus side high aspect ratio confers higher lift-drag ratio, everything else being equal. So probably worth keeping.

    rself

    PS-Is there a fore-aft seam down the middle of the main panels? The lens seams are clear but I think I see a middle seam too, maybe not?

    Last modified: 14 Jul 2019 16:11 | Anonymous member
  • 14 Jul 2019 13:27
    Reply # 7778783 on 7777985

    Hi Graeme

    Thanks for posting the pictures.

    It looks good and obviously works :)

    Rob

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