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S2 6.7 Junk Rig Conversion

  • 17 Nov 2018 23:30
    Quote
    Reply # 6912210 on 6872873
    Anonymous member

    Hi Arne,

    Thank you for the help and support. I have two of the four paper patterns drawn. I would not say that I am now 'good' at making patterns, but I am probably about as good as I will ever be. The maximum rounding points are where they should be at 0.35B and there is a straight taper to the leech. 

    It would be really great if there was someone anywhere near me that could take at look at these big paper drawings and tell me if they look approximately correct. I have not had much luck capturing the pencil lines using my cell phone camera. All the pictures look like big pieces of paper taped together, the lines are not clear. Since it seems like I am the only would-be junkie in the region I guess checking all my numbers three or four times through the whole process will have to be enough.

    I hope you or someone else can check a few assumptions I am making. I have seen 'Odyssey III' mentioned here on the JRA forums. The only product I find with that name is called simply 'Odyssey' without the 'III" at the end. I assume that this is the same material. Will the material currently made by Marlen Textiles called 'Odyssey' be acceptable for sail cloth? I like the way it looks and feels on the sample card. As long as I am careful to keep the shiny (coated?) side of each panel on the mast side I think it will look really nice.

    As far as thread goes I have been assuming that I can just get a spool of whatever sailrite.com suggests as the best match for the Odyssey color I order. Does this sound like a good plan or do I need to make sure I get something with specific material properties such as strength and size? Would a contrasting thread color be better than a matching color for some reason?

    I am slowly making progress ... I think.

    Scott.


    Last modified: 17 Nov 2018 23:32 | Anonymous member
  • 13 Nov 2018 19:54
    Quote
    Reply # 6903085 on 6872873
    Anonymous member (Administrator)

    Scott,

    if that (lengthened) spline is curved as it looks (and to the calculated max round), you will be all right. Personally I add another nail or two closer to the luff to increase the curve of the spline there, but I don't torture the spline in any way, and I make sure that i don't move the max. camber point forward of the planned 35% from luff.

    Arne

    Last modified: 13 Nov 2018 19:57 | Anonymous member (Administrator)
  • 13 Nov 2018 18:57
    Quote
    Reply # 6902933 on 6872873
    Anonymous member

    Arne,

    I will double check the length along the battens, and the luff and the leech for accuracy.

    Will something the size of the trim in my pictures, but longer, make an appropriate rounding shape?

    Scott.
  • 13 Nov 2018 10:16
    Quote
    Reply # 6902214 on 6872873
    Anonymous member (Administrator)

    Scott, 

    I guess I would give highest priority on getting the length along the battens the same, and then the length of luff and leech. If they are ok, a diagonal a bit off can only mean that the rise angle is not exactly right. That is not such a big deal. Weather the rise angle is 9.7°, 10.0° or 10.3°, is hardly noticeable (but it shows on the diagonals). This practice will ensure that the luffs of the four lower panels are straight, and that the panels fit together along the battens.

    When bending that spline to get the right round, I place a nail at that 40% point. The idea is that the spline should not need to be forced into position at the aft end, but ‘find’ its position, thanks to the ‘40% nail’.

    Accuracy:
    Remember that this is not rocket science. We should be very satisfied with approaching 3-diget accuracy, and in most cases two digits is the best we can do. I mostly make my drawings with millimetre resolution, but am more than happy if I get close to the nearest centimetre during lofting and sewing.

    The problem with getting the patterns perfect, only shows that practical construction of stuff is very different from producing accurate (computer) drawings. When I developed my ‘chain calculator’ method for finding the needed round and camber, others soon developed computer programs to do the job better. They surely produced results with impressing numbers of digits, but my guess is that the needed fudge-factors built into their algorithms did not produce more accurate camber than my primitive chain method does.

    Finally, this shows the superiority of using paper patterns  -  much cheaper to do errors on paper than on the canvas ☺...

    Arne
  • 13 Nov 2018 01:46
    Quote
    Reply # 6901837 on 6872873
    Anonymous member

    Thank you for the feedback, Arne.

    Truth be told I used an Excel spreadsheet to do all the scaled calculations. I found your advice sound. It was easier to print out and mark up your master sails than to try to get a precise drawing in QCAD.

    I am in need of some assistance. I have the parallelogram for Panel 7 (the one with the boom at the bottom) lofted full size on some red rosin paper. After using the baseline and rise method I ended up with one diagonal that is right on the expected length and the other being off about 3mm. Unless someone advises me otherwise I will assume that 3mm is OK that not spend time looking for what corner is not completely square. 

    I am now attempting to loft the round in this panel. The only other curve I have lofted was on my Puddle Duck. The rocker on that boat plan has 7 stations for an 8-ish foot long rocker. It was almost impossible to get the curve wrong.

    I have a nail at the tack, one at the max round point and one at the leech of the boom. I also see a note from Arne that the aft 40% of the round should be a straight line. I am really puzzled on how to draw the correct curve using only three points. It seems that the minimum I need is an additional point marked at the start of the 40% aft section that should be straight. That would allow me to clamp a bendy batten to 4 points and get a deterministic shape.

    I am also wondering if the 'batten' (the least expensive trim I could find at the home improvement store) might not be stiff enough for this task. I expect the stiffness will change the shape significantly.

    Is there something obvious that I have overlooked for this part of the full size paper lofting? I attached a few photos in case that is helpful. I expect I need something longer than the 8 foot trim I have now. I have put off buying a longer length of trim until I have some confidence that it is the right thing to use.

    Right now I am really happy that I did not go for a fan sail with many different panel shapes. Making 4 patterns is going to be plenty of work!

    Thank you in advance for any help.

    Arne, I saw in a different thread that you are back home after a hospital stay. I hope you are doing well and recovering.

    Scott.

    4 files
    Last modified: 13 Nov 2018 01:54 | Anonymous member
  • 09 Nov 2018 11:46
    Quote
    Reply # 6896213 on 6872873
    Anonymous member (Administrator)

    Scott, you seem to follow exactly the procedure I hoped that users of Chapter 3 and 4 of TCPJR would use (..note that i wrote users, and not readers…). In other words, print out the master sailplan you fancy, and then spend an hour with a calculator to scale up or down the sail. Maybe not as elegant as when using a CAD program, but you will soon be ready for lofting patterns, this way. That is what this is about.

    Arne

    Last modified: 09 Nov 2018 19:43 | Anonymous member (Administrator)
  • 08 Nov 2018 00:31
    Quote
    Reply # 6893951 on 6872873
    Anonymous member
    I think I really made a decision this time. I have started following the process laid out in The Cambered Panel Junk Rig by Arne K. I am using Arne's suggested 2.05AR sail from his drawing earlier in this discussion.

    22 Sqm, 2.05AR and 8% 'barrel method' camber is the plan.

    Down stairs I have plywood on the floor as a work surface and I have Sheets 1 to 3 marked up with the sail plan details. Right now I am not completely sure how to draw the locations and size of the batten pockets for Sheet 4. I think this can wait until just before I start marking the canvas to cut.

    I hope to loft at least one or maybe two panels full size on paper this week. If anyone has time to look at my scribbling and inform me of any obvious errors I would appreciate it.

    I am also looking forward to getting my Odyssey color samples. On order from Sailrite!

    Scott.

    1 file
    Last modified: 09 Nov 2018 14:20 | Anonymous member
  • 02 Nov 2018 00:33
    Quote
    Reply # 6884971 on 6884907
    Anonymous member
    Scott wrote:

    I think I am on my own now. The Faintail sail, Arne's sail and the Weaverbird sail all seem to have different advantages. I find it harder to make a choice when all the options look good. 

    Somehow I will need to decide for myself what features are most important for the sailing I am likely to do. 

    Scott.

    Depends what you want, if you want ease of reefing coupled with known performance and handling, then Arne's sail which is standard HM is the way to go. Cambered or flat, it is now well understood and it works well. Any of the others is a bit of an adventure.

    However, I really see no point in a flat sail. Cambered sails work and work well, unless you are building a mizzen which will double as a riding sail, for that purpose, flat makes sense.


    Last modified: 02 Nov 2018 00:35 | Anonymous member
  • 01 Nov 2018 22:52
    Quote
    Reply # 6884907 on 6884609
    Anonymous member
    Anonymous wrote:
    Scott wrote:

    The answer is going to be "Don't do that!" but ... Is there one of these two that will clearly work better than the other if the sail panels are cut completely flat?

    The answer is going to be "Do do that!", because although we've said that it doesn't make much sense to make a flat sail these days, knowing all that we know now; you still want to find out for yourself.

    But, do it with a polytarp sail, so that you make a minimal investment in finding out what works and what doesn't. Cut your shape out of one big tarp, add some pockets very quickly, made out of the offcuts, and make a rolled tabling around the edges, not webbing (to save money). This sail should last a summer or two. Put your initial permanent investment of work and money into getting a tabernacle and mast into the boat.

    First, though, you'll have to decide on what kind of sailplan, in order to know where and how long the mast has to be.


    David,

    Thank you for the very well reasoned advice regarding a polytarp sail. I agree it makes sense for me to learn about flat sail performance at a lower cost and then later build the final sail with a quality long lasting material.

    I think I am on my own now. The Faintail sail, Arne's sail and the Weaverbird sail all seem to have different advantages. I find it harder to make a choice when all the options look good. 

    Somehow I will need to decide for myself what features are most important for the sailing I am likely to do. 

    Scott.
  • 01 Nov 2018 19:17
    Quote
    Reply # 6884609 on 6883177
    Anonymous member
    Scott wrote:

    I will try to put the "tall tabernacle" out of my mind. Thank you for the response.

    Seems I am back to not knowing what to do, so I put the Fantail sail and the Weaverbird sail on top of the line drawing of the original rig. Maybe I should rig it so I can swap back and forth between the two? (A joke, of course).

    I think the answer is going to be "Don't do that!" but ... Is there one of these two that will clearly work better than the other if the sail panels are cut completely flat?

    Scott.


    The answer is going to be "Do do that!", because although we've said that it doesn't make much sense to make a flat sail these days, knowing all that we know now; you still want to find out for yourself.

    But, do it with a polytarp sail, so that you make a minimal investment in finding out what works and what doesn't. Cut your shape out of one big tarp, add some pockets very quickly, made out of the offcuts, and make a rolled tabling around the edges, not webbing (to save money). This sail should last a summer or two. Put your initial permanent investment of work and money into getting a tabernacle and mast into the boat.

    First, though, you'll have to decide on what kind of sailplan, in order to know where and how long the mast has to be. The Fantail planform will work better than others, as it adds some camber by the fiendishly cunning chinese method of allowing the upper, fanned panels to twist a little. These panels can be flat, even if, later, you come to realise that the lower panels can have and should have had some shape sewn into them. 

    Having said all that, later on when you've experienced a flat sail and got bored with sailing to windward slowly, you could do as I've one, and add camber by putting double cone hinges into the lower battens of a flat or near-flat sail. This way, you retain the one good thing that a flat sail has going for it: its docility.
       " ...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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