Creating camber in the panels, with or without broadseams.

  • 20 Jan 2017 21:06
    Reply # 4559756 on 4559079
    David Tyler wrote:[I copied this across from the Roger Taylor 3H topic, to this more appropriate topic]
    Thank you for keeping topics appropriately organised, David.  Future seekers of information will thank you for that.
  • 20 Jan 2017 16:00
    Reply # 4559079 on 4322040
    Arne Kverneland wrote:
    Jami Jokinen wrote:

    Arne,

    EDIT: Is there a way to gradually increase the camber (larger in the lower panels) using the barrel cut and amateur batten pocket methods?

    I see that many have introduced the practice of gradually reducing the camber in each panel as they move upwards in the sail.

    In all the cambered panel sails I have designed, made and used since 1994 (six sails on six boats), I have made all the parallelogram panels with the same camber; 8 or 9% camber/chord. I have never ever thought, “Oh, I wish I had cut panel four and five flatter than the lower ones”. I only make the transitional panel flatter and then the two top panels even more so.

    However, if you insist that you still want to gradually reduce camber as you move upwards, here is how I would have done it:
    I would
      first cut out the paper pattern for the lowest panel (with most camber and thus round) and use it for cutting out that panel. Then I would recut the pattern with the reduced round required for the next panel, and cut that panel out, etc, etc. This would be a quite quick process, as it lets you re-use the pattern 3-4 times.

    Arne


    [I copied this across from the Roger Taylor 3H topic, to this more appropriate topic]

  • 20 Jan 2017 12:41
    Reply # 4558715 on 4322040
    Jami Jokinen wrote:

    Is there a way to gradually increase the camber (larger in the lower panels) using the barrel cut and amateur batten pocket methods?

    [I copied this across from the Roger Taylor 3H topic, to this more appropriate topic]

    The upper edge of the lower panel, and the lower edge of the upper panel, as they meet at a batten, should have the same curvature, to make them match as you sew them together. That doesn't prevent you from reducing the curvature on the upper edge of a panel relative to that on the lower edge of the same panel, so as to reduce the camber towards the top of the sail.

    Last modified: 20 Jan 2017 13:01 | Anonymous member
  • 31 Oct 2016 11:38
    Reply # 4357104 on 4322040
    Anonymous member (Administrator)

    When everything fails, read the instruction!

    Somehow, I only opened Slieve’s spreadsheet, and missed the instruction in his Appendix 3. With the instruction in hand, the spreadsheet was easy to use, of course, even for me.

    Now, I found I would compare the spreadsheet’s results on Round against the results I got when using my Chain Calculator. I used my master sails and simply picked my results from Fig. 4.5 in my Chapter 4 of TCPJR, page 7.

    In my updated version of “Arne’s Chain Calculator” I suggest a quicker method of finding the needed Round, by just setting it to 0.55 times the wanted depth of camber (in mm). This hits pretty close on my sails as long as the wanted camber/chord is around 8% and the AR of the sail is between 1.85 and 2.05 (p/B between 0.209 and 0.234). With a lower or taller sail, or with a deeper or flatter camber in mind than 8%, I think the real Chain Calculator will hit closer. Still, I don’t try to say that the Chain Calculator is in the Rocket Science  League, when it comes to accuracy...

    After having tried Slieve’s spreadsheet, it appears that he has used the simplified version, i.e setting Round = 0.55 Camber. Moreover, the algorithm for calculating the Round has no parameter in it for panel-height to batten-length ratio, p/B in it.  I have found when playing around with my Chain Calculator, that the need for Round goes down when the p/B ratio goes up.

    Below is a filled in spreadsheet, used on two of my master sails, one with AR=1.90 and one with AR=2.20. For comparison, I have filled in the results from my chain calculator in parentheses.

    Arne


    Last modified: 31 Oct 2016 11:45 | Anonymous member (Administrator)
  • 24 Oct 2016 12:35
    Reply # 4329530 on 4322040
    Those planning to make a cambered panel sail will doubtless find David's and Arne's ideas here useful. I made mine following the recipe given in Slieve's ''Thoughts on Cambered Panel and Split Junk Sails'' files. His calculator automatically provided the breadth and depth of broadseam required to produce a 3D cambered panel after I had entered the dimensions of the panel and depth of camber required. Appendix 3 explains the procedure.

    Look under the rubric ''Junk Information''; ''Public Domain Files: Slieve McGalliard''. I can't say the sails I made using this resource, (6% camber in the lower panels), are especially beautiful, (photos in my profile page), but Branwen's performance under them has proved satisfying and I'm grateful to Slieve for his guidance.

  • 23 Oct 2016 16:33
    Reply # 4328406 on 4322040
    Anonymous member (Administrator)
     

    David,

    I think we are approaching something useful now. I looked up in my latest version of the “Arne’s Chain Calculator”. This has mainly dealt with the very large round needed along the battens to get enough bagginess. I have touched the matter of horizontal stretch in the cloth as well, but never quantified it.

    Look at the very fresh photo below left. Today I have done some practical “camber measurements” on my garden fence: I fastened two screws at a horizontal distance of  4.9m (= B on Ingeborg). Then I hung a Dyneema line on the one to the left and put a 4.9m mark on it with tape in the right end. Mid between the two screws, I measured up marks, 30, 40 and 50cm down from the horizontal screw-to-screw line. These points represent the 6, 8 and 10% camber. Then I moved the tape mark in an out from the right screw, horizontally, until the line sunk to the  30, 40, and 50cm marks.

    The first thing I noted was that it takes very little horizontal movement (slackening) of  the line until the bight sinks to 2, 3 and 4% “camber”. For this reason, one needs not bother with slackening the sail along the yard and upper 2-3 battens, where the sail is planned with little camber.

    The result of today’s measurement was that it took...

    ·         5.0 cm (= 1.0% of 4.9m) slack to reach about 30cm or 6% camber,

    ·         9.5 cm (= 1.9% of 4.9m) slack to reach about 40cm or 8% camber and

    ·         15cm (= 3.1% of 4.9m) slack to reach about 50cm or 10% camber

    Those 9,5cm to get 8% camber coincides well with the 8.7cm I got when measuring the length of the 8% curve in the CAD-drawing, below (there I used a number of 100mm radius circles along the curve to measure it).

    Practical use of my findings.
    Sooo, theoretically I should shorten the sail of Ingeborg’s dimensions 9.5cm in from the B=4.9m mark on the batten (foreward  end). That is a shortening of 1.9% of B. However, with the look of Johanna’s blue sail in mind, with her D-shaped vertical panel curves, I think I would only slacken the sail with 70% of what my measurements above suggests.

    Then, to get...

    ·         6% camber, I would shorten the sail 0.71% of the batten length B along the batten,

    ·         8% camber, I would shorten the sail 1.4% of B (6.9cm in Ingeborg’s case)

    ·         10% camber, I would shorten the sail 2.1% of the batten length, B.

    One has a choice on what to do about the excess cloth along the battens:
    One may leave it as it is, where it will show as wrinkles (less than on Johanna, more like on Frøken Sørensen), or one may shorten the sail the same length by inserting 2-3 tucks along the rounded batten panel edges before assembling the panels.

    I think that by using these numbers, the sail will inflate well in light winds and hit quite close to the planned camber. The vertical curve should end up closer to the box section  in Frøken Sørensen’s sail than the D-section in Johanna’s sail.

    Arne

     

    Last modified: 24 Oct 2016 08:49 | Anonymous member (Administrator)
  • 23 Oct 2016 12:55
    Reply # 4328239 on 4322040

    Arne, how about this as a rule of thumb for adding tucks?

       1. The curved edge of a barrel-cut panel is longer than the distance directly from corner to corner along the surface of the cloth.

       2. The length of the straight edge of a 3D panel is shorter than the distance from corner to corner, measured along the surface of the cloth.

       3. Therefore, if tucks (or darts, as our JR Glossary calls them - interchangeable terms) are added to the edge, they should be such as to make the edge of the panel equal in length to the distance from corner to corner, measured along the surface of the cloth.

    3. will result in a condition midway between 1. and 2., where some excess length of edge has been removed, but some slackening of the panel edge along the batten will still be needed, just not as much as if no tucks had been added - allowing for some fine tuning of the camber, as you've described.

  • 23 Oct 2016 10:36
    Reply # 4328207 on 4322040

    David - I've probably got the nomenclature wrong. Firstly, I was referring to panels formed from one continuous cloth. The point I was making was that, using Arne's method, when sewing the top or bottom edge, one gathers the material into multiple small tucks, to reduce the overall width of the sewn edge to the designed width of the panel, thus inducing the camber. No material is removed from the panel, so there is more of it, close to the head and foot of the panel, to create the 'box' effect. If, instead of simply oversewing the gathered material, one developed each tuck into a sewn-in pleat, - effectively creating broadseams - then the available sail area close to the head and foot would be reduced.

    I was merely thinking that is how Arne achieves the box-section shown in his recent post. I quite agree that having more canvas than necessary flapping around, especially when under reduced sail offshore, is to be avoided.


  • 23 Oct 2016 09:21
    Reply # 4328159 on 4328067
    Anthony Cook wrote:

    It seems to me that using tucks, rather than broadseams, will create more of a 'box section.  With tucks, the full amount of sail material is available virtually right up to the head and foot of the panel, creating more fullness in those areas. With broadseams, the sail material contained within the sewn seam is lost for ever.

    I don't think I'm following your reasoning here, Anthony. Both tucks and broadseam can be applied in the same way, to obtain a 3D shape at the edge of a panel that is reasonably close to the ideal shape obtained with an added, lens-like shelf. Tucks are used where the panel is formed from one continuous cloth, and broadseam is used where there are vertical seams between a number of cloths that make up a panel, but each can do what the other can do, in terms of forming a 3D shape.

    My experience has been that it's inadvisable to try to get a completely rectangular cross section to the panel. This seems to put too much cloth into the sail, too close to the batten. Better is to aim to create an angled shelf. Angles of 30 and 45 degrees seem to lend themselves to easy calculation, as one can use a "1:2:√3" or "1:1:√2" triangle to work out the offsets.

    Last modified: 23 Oct 2016 12:57 | Anonymous member
  • 23 Oct 2016 09:14
    Reply # 4328153 on 4322040
    Anonymous member (Administrator)

    OK, David

    If I am to produce some useful and understandable info about this, I guess I should first make one single, full size batten panel and fit it on a frame and take is out for a dry-sail. Then I can vary the stretch along the battens, and even try with temporary tucks and see how it looks. With the result from this test I should be able to write a rule of thumb which at least I can understand...

    Arne


    Last modified: 23 Oct 2016 09:16 | Anonymous member (Administrator)
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