S2 6.7 Junk Rig Conversion

  • 28 Nov 2018 13:27
    Reply # 6936255 on 6872873

    Asmat,

    Your photos clearly illustrate why I do not use, and strongly advocate against using  boltrope or webbing on the leech of a JR sail. When that sail was new, it is clear that the boltrope was just a little too tight, and the leech is hooking, just a little. When the sail has aged, the rope has stretched, and is no longer supporting the cloth, which has stretched and broken down. When two materials have different stretch characteristics, which then change as they age, it is impossible to get them to work together. Seatbelt webbing simply cannot be matched with common sailmaking cloths. This is not sailmaking; it is canvas work, where the finished item is rarely under the conditions of being tensioned and expected to take a pleasingly fair and well defined shape. I do not accept for one moment that a 3D JR sail panel needs this kind of canvasworker's approach, that Arne defends so eagerly.

    I will say again, for what feels like the umpteenth time: the right way to construct a leech is the conventional sailmaker's way: firstly, to lay the cloths that make up the panel either parallel or perpendicular to the edge, within 5˚, and secondly, to finish the edge with a sailmaker's tabling about 50mm wide, either rolled (like a garment hem, turned in twice), or a separate piece of cloth, threadline parallel to that in the cloth of the panel, folded in half and sewn on over the edge). That is all that is needed, but a doubler, 200 - 300mm wide, added to the edge before the tabling, mitigates against breakdown of the cloth in the long term.

    In the days of sailmaking in natural fibre, it was a very skilled job to rope a sail. The boltrope had to be just a little bit tight on the luff and foot (and the head of a gaff sail), but that was OK because the tension, and therefore the stretch, on those edges was adjusted with the halyard and outhauls. Boltrope was never applied to the leech, for the reasons given in my first paragraph (except for storm sails, when set was secondary to overall strength). In a JR sail, we do not have control over the tension in the luff and leech, so we cannot control stretch.

    Just because traditional Chinese sailmakers used a boltrope does not make it right. A look at old photos of junks rarely impresses one with the set of the sails. Did they look at Western sailmaking practice and copy it without understanding? I don't know, but I suspect so. Their sails used to be made from rattan, but when they started using western canvas, their old methods would not apply. So, what to copy? The visiting tea clippers etc.


    Last modified: 28 Nov 2018 14:53 | Anonymous member
  • 28 Nov 2018 10:43
    Reply # 6936081 on 6872873

    I did indeed use Vincent Reddish's traditional Chinese sailmakers' technique. A light line was sewn into the hem all round the sail. A 10mm braid on braid rope, visible in the photo, was then seized to this through the cloth at regular intervals. It may be that this rope stretched enough to pull the sail out of shape. Branwen's sails use seat belt webbing bolt ropes.

    I agree with David that the belly of the sail is too far aft. I think that with a stretchy cloth like Odyssey, the draught tends to get blown aft. As Lord Curzon said, "it is inevitable, therefore it is accepted".



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  • 28 Nov 2018 09:06
    Reply # 6936044 on 6872873
    Anonymous member (Administrator)

    I am an eager defender of the use of a strong boltrope around junksails, at least when the sails have been cut with baggy panels. In these sail (unlike in flat sails) all the vertical loads move out from the sailcloth to the bolrope. The load is highest at the leech, where the sheet is pulling.

    This is how the Chinese sailors got away with fairly weak sailcloth: The yard, battens and boom, connected with boltropes, formed the framework. The sailcloth was just there to catch the wind and deliver the force to the nearest edge of each batten panel.

    This only dawned to me when reading an article of Vincent Reddish in Practical Boat Owner (reprinted in JRA NL 22) a long time ago.
    I therefore conclude that a strong boltrope is an absolute must if the sail is made with baggy panels. On the other hand, with this in place, either in the shape of a handstitched on rope, or a machine-sewn webbing, there is no need for strengthening patches in the sails’ corners. Keep pulling on the sail via the battens and boltropes, and the sailcloth will see little stress.
    The photo below shows the peak corner of my Ingeborg’s sail. The hoop ensures that the load is taken by the boltrope, not the cloth. I have used this method on a number of sails now without signs of overstressing the cloth.

    Arne

    PS: As for UV-resistance and Odyssey, I cannot tell, since Stavanger at 59°N has less problems with UV-radiation. Still, I now use sail cover over Ingeborg’s sail, just to be sure.

     


    Last modified: 28 Nov 2018 09:18 | Anonymous member (Administrator)
  • 28 Nov 2018 08:26
    Reply # 6935998 on 6935419
    Arne wrote:

    Asmat,
    I would not blame the sailcloth here. To me it appears that the boltrope at the leech has been way too weak, or even non-existing. This has pulled the shape out of the panels, in particular on the upper ones, where the loads are highest. I once wrote a note on that when I discovered that the webbing for my Johanna’s sail stretched too much. The remedy was to hand-stitch on a second boltrope (a length of old halyard.).

    Arne


    Yes, I'm seeing a stretched leech in the upper four panels, but also poor shaping of the lower panels with the draught too far aft, and stretch in the body of the cloth of the top two panels. There could have been a little more tension on the THP to get rid of the diagonal wrinkles, but this would not have made the sail look as good as it should - it's clearly stretched out of shape. I lay the blame chiefly on the cloth, with its loose weave and large proportion of filler resin, but partly on the design and construction of the sail.
    I think I remember that Donald Ridler crossed the Atlantic with JR sails made from old bed sheets, so poor quality cloth can be used, but really needs to be paired with good sailmaking technique, laying the cloth in the correct direction with warp/weft in line with the loadings, and adding patching and reinforcing where needed. The latter would include a wide doubler down the leech and multiple patches at corners and batten ends.

    All in all, Odyssey doesn't seem to be a good choice, amongst the cover-type materials. The slightly heavier ones, Weathermax, Top Gun 9, Top Notch 9, Surlast etc seem to be more firmly constructed.

    Scott, that Polyester Ripstop that you found is unbeatable on price. It could be used, but only with due regard to design and construction, as noted above. It won't make a world-girdling sail, but should be good enough for light duty summer leisure sailing.

  • 28 Nov 2018 06:49
    Reply # 6935959 on 6872873

    I'm afraid I'd have to agree with Asmat, at least from a New Zealand perspective.  Quite a few of us have found that the fabric doesn't seem to like the sun very much and, in my own opinion, will start to come apart if only moderately loaded.  I wouldn't use it again, but Arne seems to have been very happy with it.  Although I didn't feel that my sail failed because of sun damage, considering Arne's success, it is the only sensible conclusion to draw.

  • 27 Nov 2018 21:35
    Reply # 6935419 on 6872873
    Anonymous member (Administrator)

    Asmat,
    I would not blame the sailcloth here. To me it appears that the boltrope at the leech has been way too weak, or even non-existing. This has pulled the shape out of the panels, in particular on the upper ones, where the loads are highest. I once wrote a note on that when I discovered that the webbing for my Johanna’s sail stretched too much. The remedy was to hand-stitch on a second boltrope (a length of old halyard.).

    Arne


    Last modified: 27 Nov 2018 21:36 | Anonymous member (Administrator)
  • 27 Nov 2018 16:57
    Reply # 6934974 on 6872873

    I wouldn't use odyssey for a cruising boat. The photos attached show a sail made of odyssey3 in 2011 and under new ownership a year later.

    Sorry, can't flip the 2011 picture right way up.


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    Last modified: 27 Nov 2018 17:01 | Anonymous member
  • 27 Nov 2018 14:08
    Reply # 6934708 on 6872873
    Anonymous member (Administrator)

    Scott,
    there is a trap which is easy to fall in  -  the paralysing fear of making something which isn’t perfect.

    Relax, most cloths that are rot-proof and wind-tight will do. If Odyssey can be had at a reasonable price, then go for it. The sail will come out at about 7kg. It is on the stout side, but on the other hand, it will stand quite brutal handling and resist some chafe. Besides, it sews very well without pucking (at least on my machine).

    Arne

    (.. playing in the cheap, available and good enough league...)


  • 26 Nov 2018 19:53
    Reply # 6933427 on 6933250
    Anonymous wrote:
    Anonymous wrote:

    I ordered small sample swatches for several different fabrics and also two yards of the POLYESTER RIPSTOP (DWR) - 2.6 OZ. I am not totally sure what I am going to do other than pull on them to see how they 'feel' and then maybe check that my sewing machine can stitch through several layers.

    Here are my findings for lightweight cloth...think parachute, kites, hot air ballons:

    A, B, C

    Turns out your linked source above beats them all.

    rself

    Thank you for the reply and the links to lightweight fabric. In your profile I see that you are using Odyssey III for your sail. Do you have any experience using lighter cloth for a junk rig sail? It seems like everyone is using Odyssey or an even heavier fabric.

    Last modified: 26 Nov 2018 19:54 | Anonymous member
  • 26 Nov 2018 18:18
    Reply # 6933250 on 6922769
    Deleted user
    Anonymous wrote:

    I ordered small sample swatches for several different fabrics and also two yards of the POLYESTER RIPSTOP (DWR) - 2.6 OZ. I am not totally sure what I am going to do other than pull on them to see how they 'feel' and then maybe check that my sewing machine can stitch through several layers.

    Here are my findings for lightweight cloth...think parachute, kites, hot air ballons:

    A, B, C

    Turns out your linked source above beats them all.

    rself

    Last modified: 26 Nov 2018 18:19 | Deleted user
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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