Backstay problem on Gunter rig

Discussion in 'Sailboats' started by laukejas, Oct 19, 2013.

  1. Petros
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    Petros Senior Member

    alloy frame will always cost more than a wood frame. though metal tools are not too costly, hand held is all you need (hack saw, hand held rivet gun, drill, file, etc). You would not have to weld much if you use al gussets riveted to the tubes for attachments. I think wood is nicer to work with, and nicer to assemble and handle in cold weather. Alloy will likely be lighter to transport, but the extra weight of wood might be beneficial in the water. I also think wood is more attractive after it is finished, it is also easier to repair, particularly temp field repairs.

    You can pick either one and have a successful boat. Skin on frame has been built a lot of different types of frames, just pick the one you are most comfortable with using. I like working with wood, and it cost less, so I stick with it.

    There are several ways to make a dagger board box work on a folding skin boat; one way as you have seen, is you make a fabric sleeve attached to the bottom of the hull fabric. the sleeve comes up inside a frame and fastens near the top. You insert the dagger board down through the sleeve. Simple and effect, one minor issue is you could wear holes in the sleeve eventfully with lots of usage of sliding dagger board in and out. fairly easy patch however.

    The other means is to make a light weight and water tight dagger board box and attached it to the bottom of the skin with screws and caulk. so it stays attached to the skin, and is supported by the frame when assembled, it gets folded up with the skin when stowing it. You just have to regularly inspect and repair/seal where the fabric is attached to the lower edge of the box.
     
  2. Nnnnnnnn
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    Nnnnnnnn Junior Member

    Two small comments/
    May be you can import some Al tubing from Kaliningrad or Belarus? Not too much to avoid custom tolls. ;)
    Look at your parents kayak frame, no soldering only rivets and bolt&nuts.
     
  3. Nnnnnnnn
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    Nnnnnnnn Junior Member

    To improve fairness of bottom lines, on this boat are used inflatable inserts between frame and skin.
     
  4. laukejas
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    laukejas Senior Member

    All right, I guess I'll stick with wood based design then. I'll start working on the design, and will post here when it's finished. Thank you very much for information and insights! It is indeed very helpful.

    Just a quick question - if stringers are wooden, must these joints be with alloy sleeve on both stringers? Because it will be hard to attach the male insert to the wooden stringer. I reckon someone wrote that the wood might swell when wet and get stuck in alloy sleeve, that's why similar alloy insert is a must. But I don't get this - if these stringers are covered in waterproof varnish, can they really swell that much? And if they do, isn't it possible to sand them down a bit to smaller diameter and re-apply varnish, once I notice they tend to get stuck?
     
  5. Skyak
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    Skyak Senior Member

    The sleeve is the easy way to make a very reliable connection. Without the sleeve the varnish will tend to wear away or crack at the joint and swelling can make the joint unreliable. Not the only way, but worth the effort.
     
  6. Skyak
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    Skyak Senior Member

    I didn't see that. Is there a flat barrier between the tube frame and the inflatable inserts? Does the space frame disassemble for transport? This is interesting because an aluminum space frame can be as light and stiff as a fiberglass monique.

    I have been thinking that laukejas could build some structure into a cockpit floor to carry loads from the crew to the sail rig.
     
  7. laukejas
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    laukejas Senior Member

    What exactly do you have in mind? I thought that I would copy Passat's design with the seat, which seems to act as a additional structure for transferring loads between rig, centerboard, and mast. Or do you suggest some additional structure?

    As for these sleeves - well, okay... I'll try to think of some way to make them with aluminum inserts.
     
  8. Skyak
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    Skyak Senior Member

    The passat has wide boards behind the sponsons and at the keel that are pinned tight to each frame. If you can build similar you should be fine. The hard part is to replicate the metal attachment hardware of the passat.

    If the boat twists when sailing I was thinking you could run wires from the corners of a solid floor -like a kingpin at the center. I would not bother unless you find there is a problem. Build like the passat and do what you can to make good connections to the frames. If you find you want more stiffness there is more you can do.
     
  9. laukejas
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    laukejas Senior Member

    Yeah, as a matter of fact, I'm working on this right now at the moment. Figured a way to attach these boards to transom and bow pieces, but as for frames, I'm yet to find a screw-less, fast to assemble solution. The perpendicular angle makes it very difficult.
     
  10. Petros
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    Petros Senior Member

    something like this works:

    [​IMG]
     
  11. laukejas
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    laukejas Senior Member

    Thanks, Petros, that would do well for stringers, but what of the side boards, such as ones seen on Passat? How to attach them firmly and simply to the frames?
     
  12. Skyak
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    Skyak Senior Member

    From my post #90

    On the Longhaul kayak there were lots of metal fasteners with pins. If I was following their method I would buy a long length of brass "piano hinge" -hinge you buy from the hardware store in long lengths of 3 to 6 ft and cut to whatever smaller sizes as needed. Then I would mount short lengths in place and push the pin out to disassemble. Then I just make a new easy to handle pin for long term use. bending drilling and filing will drive you nuts if you build these parts from scratch.
     
  13. laukejas
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    laukejas Senior Member

    Okay, Skyak, I'll review it again, thanks for reminder :)

    In the meantime, I'm half through to a basic hull solution. I think I found a way to fix the side boards to frames without any alloy hardware at all - just some basic wooden plugs. A lot of very delicate woodwork, but should be possible. Woodscrews are not yet modeled, so let's assume a lot of epoxy.
    Attaching screenshots of CAD design. All this took 2 days to complete.

    Now, what I did with transom and bow pieces, are simple sleeves out of plywood that will be cut out at predefined angle and glued, so that side boards can fit in nicely.

    First image is just general looks (don't mind big frames, I'll make some cut-outs to save weight later).

    Second image is of transom-side board joint, third and fourth - separately, for better looks.

    Fifth, sixth and seventh images - same for frame-sideboard joint.

    Next three images - how I solved (hope I solved) the joint of two sideboards longitudinally. Simple two plywood inserts on one side, and pockets on another (pockets are made with 3 layers of plywood, middle layer having cut-outs)

    Next two images - bow inserts. On the second image you can also see how I think of fixing this center deck stringer piece, whatever it is called. It was on Passat, so I transferred it here too. Idea is that it can't slide out longitudinally because of that little insert below, and it can't slide out sideways because it is held in place by side boards.

    Also attaching three images of how it fixes with the frame.

    So, that's it. In my estimations, with this kind of attachment, side-boards cannot move in any direction except away from the frame due to the nature of these inserts, and it cannot move away due to natural tendency to straighten out. Inflatables pushing them back in place also contribute to this. It should be very stiff, I think, if the frames can hold the spring action of these side boards.

    So, that's my basic idea. I'm just not sure if the board-to-board attachment will be possible to assemble when tensioning the skin. If that is a problem, I have another idea in mind.

    Of course, as I mentioned, I haven't yet worked with keel joint, keel-to-frame attachments, stringers, so these are on the way.

    But generally, am I heading in the right direction?

    P.S. All the parts, with no exception, are made out of either 1cm or 5mm plywood (these numbers are adjustable, but I thought something like this should be appropriate). I hope I can get away with only two thicknesses of plywood, so I don't have to buy a lot of different sheets)
     

    Attached Files:

  14. Nnnnnnnn
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    Nnnnnnnn Junior Member

    No.
    Look here for the details:
    http://gik.fordak.ru/index.php?topic=11274.0;all

    Certainly. This is the boat compatible with public transportation system, as many other SOF and inflatable boats from ex-USSR.
     

  15. Nnnnnnnn
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    Nnnnnnnn Junior Member

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