Advice on Low Aspect-ratio sail for new boat

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  • 24 Jun 2018 16:42
    Reply # 6337873 on 6330157
    Anonymous member (Administrator)


    Here I have played with that sailplan. I have made it oversize, so that when the shown tucks have been added, it will take the shape and sail area of the sail to the left, the one I drew up for your boat.

    This is a quick way of getting a bit camber in the sail.


    PS: You will have noticed that I not only work in metric; I also jump between metres, millimetres and centimetres. Sorry about that. Actually, for sailmaking, centimetres, cm, is the handiest size. I calculate to the nearest tenth of a cm (= mm), but I round off the final numbers to whole cm (around 3/8") when starting to loft the sail.

    Last modified: 24 Jun 2018 16:52 | Anonymous member (Administrator)
  • 24 Jun 2018 14:41
    Reply # 6337671 on 6330157
    Anonymous member (Administrator)


    I have a 2-D CAD program, called QCAD. Such programs let one draw different bits in different layers.  I imported your sailplan under a layer I called 'imported JPEG'.

    This ends up in a wrong scale. Then I added two more layers, one called Waterline and one called helping lines. The waterline you can see in blue; I just drew it up on freehand. With two vertical helping lines from the bow and stern, down to the waterline, I suddenly had the length of the boat, as it came out. The whole drawing, all three layers, was then expanded to make the boat  24', or 7.315m in my numbers. 

    The hull, mast and mizzen mast and sail were then traced into 3 different layers.

    Then I was ready for importing one of my master sailplans (also in QCAD), chopping off the lowest panel and scale it down until B= 4.10m. This was trial fitted on the boat, and I think it looks good. The moderate aft rake of the main mast (about 2deg.) appears to suit the sail just fine, and gives a good angle and sufficient drift between the mast top and the halyard's slingpoint at the yard (5% aft of the middle).

    There are some more stuff to be found about this here.


  • 24 Jun 2018 13:56
    Reply # 6337662 on 6330157

    That was very quick and very interesting. Thank you, Arne.  How did you do that sketch over my photograph, then isolate your one?  

     Anyway, I like the sail.  I think you have a point, there. 

  • 24 Jun 2018 09:50
    Reply # 6337554 on 6330157
    Anonymous member (Administrator)

    Hi David,

    Here I have done a bit copying and. pasting. From a stack of master sails that I have, I took the lowest sail and removed the lowest panel, before crimping it to a suitable batten length. This sail makes better use of the mast you have drawn up.

    This lets you either skip the mizzen for now, or make it smaller, and move the mizzen mast further aft. I suggest you start without the mizzen, to save time.

    The sail I have drawn could be made flat, as you planned. However, there is a simple way of making a bit camber in the sail, just by fitting small tucks at the luff and leech. The red sail below was modified to have camber this way. If you are interested, I can redraw the flat sail, to the necessary oversize. When you make it and then add those tucks, it will crimp back to the shown size.

    The extra work of fitting those tucks will be less than five hours, and it will pay back in better performance.

    Good luck,

    Last modified: 24 Jun 2018 09:51 | Anonymous member (Administrator)
  • 24 Jun 2018 01:44
    Reply # 6337413 on 6330157


        The main plans I work off are a big pencil drawing, too light to show up in  a photo.

    I did something in pen here. It doesn't have the rudder or off-center board, but the boat being flat sided, I can move the CLR as I like, so that is not a constraint. I think I may have gone small on the board, which I built to put 8 sq.ft. under water.  I can rebuild it if I must. 

    One problem, (besides my haphazard approach) is that I haven't actually weighed the boat yet and I'm not certain what she weighs dry on the trailer, much less full of humanity and gear and supplies.  My GUESS based on measuring the immersed part of the hull is that she wouldn't come in under 2500 lbs.  In that case, with 185 square feet in the main as i have drawn it and 60 in the mizzen, the combined 245 sq.ft. would give me a very decent SA/D of 21.

    I am learning LOTS in this process.  For example, that it is going to be hard to sheet a sail like the one drawn with a single sheet with the mizzen in the way.  I had hoped to sheet from the aft end of the cabin roof, but I don't think I can do it. Is there any way for me to get around double sheets?  I would almost rather do anything else. Could I extend the highest batten?   

    I could eliminate the mizzen altogether and go a bit bigger on the main and sheet from the transom, maybe?  

    The whole idea of mine was to do something quick and get out there this summer and learn about junk rig rather that being in the shop until the fall making the perfect sail.  That's why I was shying away from a Split Rig- too much work.  I wanted to make a flat sail that I can learn on and have some fun with for a season or two, then make another if I need to.  



  • 22 Jun 2018 21:28
    Reply # 6333608 on 6330157
    Anonymous member (Administrator)


    It would be very useful if you could present some profile drawing with the mast, board and rudder in place. Remember to fit some scale along the drawing, for instance showing  10ft or 5 metre on it.

    That would help any wannabe rig designer to come up with something.


  • 22 Jun 2018 20:21
    Reply # 6333539 on 6330157

    found a blog about a boat similar to yours


  • 22 Jun 2018 01:45
    Reply # 6331683 on 6330157

    everything you need for rigging and parrels etc. should be covered in the Practical Junk Rig, the tutorials are just for laying out the sail.

    It took me longer to attach all the bits and bobs to the sail that it did to make it.


  • 21 Jun 2018 23:22
    Reply # 6331376 on 6330157

    OK, mast line is in there. 

  • 21 Jun 2018 23:21
    Reply # 6331374 on 6330157


    Thanks for getting back to me.  That article certainly has what one needs to draw the Reddish sail itself. Do you know of any article that talks about suggested mast line, parrels, and running rigging?  


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