Idea for battens that *decrease* camber in higher wind speeds

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  • 19 Jan 2020 17:59
    Reply # 8621419 on 8587768

    We did "graduated" camber on Auklet's mainsail – flat on the top two panels, a little camber in the middle two, and more on the bottom two. I have consistently wished for more camber in the middle two panels, wishing that we had made them the same as the bottom two. The difference in upwind ability with the full sail up is striking – to the point that I often sail with more sail area up than I might, going upwind, just to have that extra camber. It's not a lot, but it really makes a difference.

    Shemaya

  • 19 Jan 2020 09:54
    Reply # 8618349 on 8587768

    I agree, Arne.

    On both sails for Weaverbird, hinged junk and wingsail, I only reduced the camber in the top two panels, to make a smooth transition from full camber to straight yard. I have in the past made sails with gradually reducing camber, but now I can't see any point to it. With camber of no more than 10%, the sails are fine in a strong breeze, and it wouldn't improve them in any way to make the middle panels flatter than that.

  • 19 Jan 2020 09:33
    Reply # 8618222 on 8587768
    Anonymous member (Administrator)

    .. keep it simple...

    Early in my days of cambered JR, I wondered if there could be a simple way of flattening the sail, as on Bermuda- and gaff-rigs. I didn’t find one, and since reefing and un-reefing is so quick and easy, in particular on small size sails below 25sqm, I dropped the idea. Nowadays I like to think that I tune the sail area instead of the sail camber  -  much easier. This worked exceptionally well on my small and quite tippy boats; the 5.5m Broremann and the 6.5m Frøken Sørensen.

    My present boat, Ingeborg, very forgiving with her big, ballasted keel, has the same sail area as the originals with Genoa 1 set. On her, as on the others, I let all the four lower panels have the same 8% camber. On top of a Force 4, I will already have dropped two panels (= mainsail and working jib), and on top of F5, I will be down on 3-4 panels (= 15-20sqm). Only these three top panels have been cut progressively flatter than the lower section.

    I have never, ever felt “ Oh dear, I wish I had cut panel 4 and 5 (from top) flatter”. Not for a single time. This makes life easier on the lofting floor, as I can produce four panels from the same pattern.

    Arne

     
    Broremann...


    Ingeborg can be viewed here


    Last modified: 19 Jan 2020 10:05 | Anonymous member (Administrator)
  • 19 Jan 2020 01:39
    Reply # 8615421 on 8599841
    Anonymous wrote:

    I think it is wonderful that people are keen to experiment with new ideas, and I keenly follow their progress.  For me, though, the answer to making a straight-battened cambered junk sail flatter as the wind increases is very simple. You have a lot of camber in the lower panels and incrementally decrease it as you go up the sail, something like 8%, 6%, 4%, and 2% in the fanned panels.  As the wind increases and you reef the sail, it flattens out nicely.  Chris Scanes built a shelf-foot sail this way some years ago for a friend of mine.

    Yes, that is how I make my sails....
  • 18 Jan 2020 12:44
    Reply # 8610302 on 8587768

    Another point that's worth making is that whenever there's flexibility in a rig, and the boat is in a seaway, there's fretting, chafe and fatigue too - the rig is trying to destroy itself from the inside.

  • 18 Jan 2020 06:53
    Reply # 8608088 on 8587768

    I should have provided a bit more explanation in my earlier post, and yes it is good to experiment. Having recently regressed back to a bermudan rig I of course now realise that the great thing about any type of junk rig is it's simplicity, and ease of handling. I have a new Code 0 for my bermudan rig yacht which I had made, and yes it does provide some exciting reaching conditions sailing, but there are a a lot of sails to put up and sheets and halyards to manage. A lot of hard work compared to the big 53 square meter single sail on our past junk rig yacht 'Footprints'. I have also experienced flexible battens on our original flat junk sail, and then the first set of battens on the new camber panel sail were far too flexible. The natural tendency of flexible battens is to develop a curve in the mid point of the sail and bend around to windward at the leech of the sail, which makes a big air brake in the after part of the sail. Any sheeting system, or other control lines developed to prevent this natural tendency for flexible battens to curve to windward when the breeze picks up is getting too far away from the what the junk rig is all about, and would add unnecessary complication. 

    Last modified: 18 Jan 2020 07:18 | Anonymous member
  • 17 Jan 2020 22:13
    Reply # 8604743 on 8599841
    Anonymous wrote:

    I think it is wonderful that people are keen to experiment with new ideas, and I keenly follow their progress.  For me, though, the answer to making a straight-battened cambered junk sail flatter as the wind increases is very simple. You have a lot of camber in the lower panels and incrementally decrease it as you go up the sail, something like 8%, 6%, 4%, and 2% in the fanned panels.  As the wind increases and you reef the sail, it flattens out nicely.  Chris Scanes built a shelf-foot sail this way some years ago for a friend of mine.


    Bonsoir

    I completly agree, both in my sailing practice and experimental practice !

    Eric

  • 17 Jan 2020 10:56
    Reply # 8599841 on 8587768

    I think it is wonderful that people are keen to experiment with new ideas, and I keenly follow their progress.  For me, though, the answer to making a straight-battened cambered junk sail flatter as the wind increases is very simple. You have a lot of camber in the lower panels and incrementally decrease it as you go up the sail, something like 8%, 6%, 4%, and 2% in the fanned panels.  As the wind increases and you reef the sail, it flattens out nicely.  Chris Scanes built a shelf-foot sail this way some years ago for a friend of mine.

  • 17 Jan 2020 10:45
    Reply # 8599784 on 8587768

    Bonjour

    I've experimented, and still do with flexible battens and what I call lambda sheeting; two sheeting points one , one third from the leech and the other at the leech.

    The rational is that I don't like, on a rather phylosophical engenierring point of view to incorporate stiffness in a flexible world. It's like having a needle next to a balloon.

    I used Mingming flat sail for the purpose. I used standard 8mm to 10mm glass polyester battens stiffen by doubling or trippling them in the forward part. It worked quite well, as such. The issues are that you need two sets of sheets (it doubles the spagethi dish in the cockpit) the forward one/third part of the sail must remain resaonnably stiff otherwise you experiement the "S bendind" of the area of the sail in front of the mast  it is both inneficient and destabilisation). As a consequence, the forward part of the sail is flat, the middle is bent and the rear is rather flat. In therms of aerodynomic it is far the optimal. It could work with additional camber in the forward part of the sail.


    The reason I continue the experimentation of the lambda sheeting is because I would like to use it to devellop a flexible junk-wingsail with forward wishbone out of the same battens (and a round leading edge out of solded steinless tubes) and flexible tail behind. I've started to build the wishbones but I have no views yet.

    Eric

    2 files
  • 17 Jan 2020 09:04
    Reply # 8599149 on 8587768

    You're right, of course, David. There's no actual need to decrease camber in a junk sail. This wouldn't be by any means a new experiment, I have a feeling it's been tried, but I can't call to mind by whom and when; but Richy appears to be inclined towards experimenting, and I never like to discourage that.

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