Freedom 40 Cat Ketch Junk Rig Conversion

  • 25 Jan 2017 18:42
    Reply # 4568359 on 1424184

    hi erik

    i use inkscape (no cad, just a vector drawing tool).
    in inkscape you draw (or import) the outline of the sail and let the program calculate the geometric center of this area. (if you have two sails, you have to combine the two shapes before the calculation).

  • 25 Jan 2017 18:41
    Reply # 4568358 on 4568332
    Anonymous member (Administrator)
    Erik and Evi Menzel Ivey wrote:

    A quick (un)related question regarding QCad - how do you guys calculate the CE for your sails?  I am using Barry's Excel spreadsheet and transfer the coordinates to QCad.  Is there an easy way of doing it in or out of QCad? 



    Not that I know about. My method is to add a few well-placed cris-crossing helping lines on the Q-CAD drawing, and then print it out to a known scale, say 1:50. Then I find CE the old-fashioned way, by cutting out the sail and cross-balance it on a ruler. Then I can just measure the position of the CE relative to those helping lines, and transfer the numbers to the Q-CAD drawing.

    BTW, the horizontal position of the CE on my range of master sails sits only about 50mm forward of the middle of the boom, so I sometimes use that for simplicity.


  • 25 Jan 2017 18:28
    Reply # 4568332 on 1424184

    A quick (un)related question regarding QCad - how do you guys calculate the CE for your sails?  I am using Barry's Excel spreadsheet and transfer the coordinates to QCad.  Is there an easy way of doing it in or out of QCad? 



  • 25 Jan 2017 12:41
    Reply # 4567742 on 1424184
    Anonymous member (Administrator)


    you are right that I use to have 10% as the default value of the balance in my sails. However, Paul J Thompson has shown that the balance may well be increased to 20% without any problem. My sails with 70° yard can easily be made to set with a balance between 5 and 15% if the mast has been made long enough for it (no problem in your case). If 20% balance (or more) is to be used, then I guess it is better to lower the yard angle, as Paul has done.

    My guess was that David’s sailplan could just as well be implemented with baggy panels as with hinges. Just remember that with baggy panels, the rules about boom rise and batten stagger when reefing do not work anymore. I use half-short batten parrels to keep the sail from moving further forward after the first panel has been lowered.


    Last modified: 25 Jan 2017 12:42 | Anonymous member (Administrator)
  • 25 Jan 2017 08:13
    Reply # 4567483 on 1424184

    The second hinge should be at 55% aft from the luff. Each hinge can only articulate +/- 10 degrees (a greater angle carries a risk of separating under load and reluctance to articulate) so to get 10% camber, two, plus a little sewn-in camber, seem to be needed. The sewn-in camber should have its maximum depth well forward - I put mine at 25% aft.

  • 25 Jan 2017 05:03
    Reply # 4567225 on 1424184

    Arne -  thank you sir! I understand your comment re only relying on camber from the cloth and in general the concept of KISS (ignoring it has been a downfall of mine so please feel free to remind me.  Often). Of concern is that if I  don't do any hinge(s), the 15% overlap increases the mast interference in comparison to your more moderate 10%.

    David -    I've created a folder in the JRA Box  and uploaded the latest drawing.  

    Sounds like the single/front hinge is similarly situated bssed on both your.  If there is a second one, is it at 60% from the luff since the camber profile is straight aft of there? Or is the idea to position it where there is still a large  of changes in curvature?


  • 23 Jan 2017 09:58
    Reply # 4563111 on 1424184

    I position the hinge (or the forward hinge, if there are two) by taking the distance from the mast centreline to the luff, and multiplying it by 1.5, and that's the distance from the mast centreline to the hinge. So, with 15% balance, the hinge would be at 37.5% of chord. I've found the articulation to be reliable at this ratio.

  • 23 Jan 2017 09:04
    Reply # 4563070 on 4563057
    Anonymous member (Administrator)
    Erik and Evi Menzel Ivey wrote:

    David/Arne - do you have some rules of thumb as to hinge locations with respect to max camber?



    Now I had to look up newsletter 24 to check the position of the fore hinge on my Malena. It sat 27% aft of the luff. Most of the time that hinge worked well, but sometimes it flicked the wrong way. I solved the problem by adding a throat hauling parrel to shift the top of the sail aft. You should be all right if you fit your (one and only) hinge to 30-35% aft of the luff, and I guess that will put the max camber point in a good position as well.

    However, the cambered panel sails have worked well for me, so I have never felt any need for bothering with hinged battens again.


  • 23 Jan 2017 08:27
    Reply # 4563057 on 1424184

    11 degrees...

    I've redrafted the the schooner sail plan with a 11 degree boom/batten angle and a 45 degree yard angle.  

     .  Link is now to my "Box" since I don't have edit access to the JRA Box at present.  If anybody wants to create a folder and move the files there that would be great.  If somebody can tell me how to get edit access to the JRA Box I'll upload and maintain the files, too.

    Some parameters that seem to come out of the drafting to date...  The batten length on the forward sail tends towards 4.3 meters or less, whereas  space wise the aft sail can support 5 meters or slightly more.   P is around 1.45 meters. This is all based on a sheeting angle of 10 degrees to the upper batten.  

    P - WeatherMax80 has a width of 1.5 meters and I am considering a separate section for the batten pockets, so the P could be greater than 1.45 if necessary.  Aesthetically, it seems to look best if the forward and aft sail have the same P though.  

    Dmin  -  This one keeps being a struggle.  It would be nice to (a) have a single sheet, (b) not have a traveler, (c) have sufficient anti-twist function, and (d) be able to reach the clew from deck.  A viable Dmin with a single sheet would then be around 1.75 to  2P.  If the lower panel is incrementally smaller than the next two, I'm just not sure if it will be sufficient.  Going to two sheets per sail makes dealing with the Dmin easier.  When cruising, four sheet sound managable. But sailing in the SF Bay shorthanded with four sheets may be a little much.  

    David/Arne - do you have some rules of thumb as to hinge locations with respect to max camber?


  • 23 Jan 2017 05:57
    Reply # 4562891 on 4562561
    ueli lüthi wrote:

    hi annie

    i see why it's better to store the files 'on site', and i do this for my stuff. but as the files are not from me, i won't upload them anywhere.

    i just said that there's no need for an own account to download files from a dropbox – even if it looks so…


    Sorry, Ueli, I was writing in haste - wanting to get to work, and got myself mixed up in the thread. I was actually asking Erik if he could put his files on our site.  It would be great if we could just upload things directly to the website and I do realise it's a bit of a bind having to join Box, but unfortunately,  Wild Apricot doesn't give us unlimited storage on the website, so using Box is the only way around it.

    I think it's fantastic the way we share our knowledge and information and have been incredibly grateful for it myself, many times.  I guess that's why I'm so pedantic about trying to organise it in an accessible way for future members.

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