Keder?

  • 01 Jul 2020 00:10
    Reply # 9070640 on 8742744

    Göran, here is another comment: I have to be honest and admit, what made me lean towards making the sail panels removable was - as an amateur first-time sailmaker - fear of managing so much cloth at the sewing machine when sewing all the panels together. The ability to remove or replace panels easily was really just a rationalisation (though later I did actually do that.) I suspect James G. will admit the same. I think Arne is right in saying you probably won't ever need to replace a panel, and on the matter of sewing all the panels together, maybe he can re-assure you about that.

    On the other hand, if removable panels really is your objective, and you decide to save a little weight by using aluminium battens - there is another way you could consider, if you have not already thought of it - that is, the "horizontal hinge" system devised by Roger T and successfully used on Mingming ll. Roger built a very robust sail on his dining room table, with the lower four panels removable from aluminum tube battens. The method he used also provided the camber. 

    Roger described it as being "like a piano hinge".


    You can see on this link https://www.youtube.com/watch?v=E-IbUt-CTRQ how Roger made his wooden boom and yard, and attached his removable panels to aluminium tube battens. A little more sewing - but probably less work and a little lighter than the double-grooved wooden battens. (And welding a "luff groove" onto both sides of a set of aluminium battens just isn't going to happen!)

    Roger's hinged panels have been well tested; another idea for you to consider.

    PS My wooden battens do bend slightly. I have not had one break, but I would hesitate to make mine any thinner. Mine are 2 x 18 x 28 = 36mm x 28mm and the sail area is about 16 sq m.

    PPS the junk rig is not simple to start with - but it sure is good and easy to handle.

    Last modified: 01 Jul 2020 00:37 | Anonymous member
  • 30 Jun 2020 17:51
    Reply # 9069966 on 8742744

    Graeme and Arne, thank you for your kind comments! Although an experienced sailer, I have no experience whatsoever of the junk rig, but it has appealed a lot to me for its simplicity (well ...) and (reported) ease of handling. I will see what modifications that can be made to my original ideas. During the short Nordic summer I will not have the time to do so much practically, having another boat (Finnsailer 35) to take care of (and use).

    The present panels will be discarded and instead used for a sun roof outside our house. And i will look for a thinner and less heavy canvas to make the panels from.

    But I´m still stuck to the keder idea. It allows easy removal of panels for modifications etc., and they are easy to handle at the sewing machine.

    Arne´s recommendation to tie the edge panels to traditionallly made boom and seems worthwhile. 

    I do not think that the present wooden battens could be made much thinner than now to preserve the stiffness to sideways bending, which is proportional to its width raised to the power of three. So thinning them only slighly may decrease their stiffness drastically. 

    So "Norway bamboo" seems to be the best option available. But then I have to abandon the keder idea. Unless (my newest toy is a MIG welder) I weld aluminium keder channels to a, let´s say, 30 mm aluminium pipe. 

    Lots of thoughts... Ideas are best before implementation.





  • 30 Jun 2020 09:58
    Reply # 9069184 on 8742744
    Anonymous member (Administrator)

    Welcome aboard, Göran!
    It gladdens me to see that someone is fitting an aux. rig to a motor-snipa. I have recently tried to lure an owner of a 20’ snipa (‘snekke’ in Norwegian) to add a little JR to it. As can be seen, the rig clears the windscreen and cockpit tent easily. I have positioned the mast a bit further forward than you as I suspect it would otherwise lead to some unwanted weather helm. Luckily there is room for shifting the sail a bit this or that way on the mast, to correct balance..

    Rudder.
    The rudder of your snipa looks better than most, so may work as it is. In case it feels sloppy with the engine stopped, it can be improved by simply adding an endplate to the bottom of it, and even a similar ‘anti-ventilation plate’ right below the water surface.
    The miniature rudder of the Polar 20 snekke, shown below, surely will need and endplate on it.

    Batten material.
    The best natural batten material is no doubt bamboo, with its tube structure. However, since it isn’t easily available in Scandinavia, I now go for thin-walled aluminium tubes (‘Norway bamboo’). On your small rig for that snipa, I am sure you get away with wood, but if you are to make a bigger rig, say between 30 and 60sqm, I don’t think wooden battens are good.

    Those tracks in the battens.
    I have seen others using variations of the keder theme for battens. Their arguments were partly that it let them replace damaged panels, and partly that it was simpler. Personally, I only see the point in quick replacing of panels in case one is making an experimental avant-garde rig. Yours appears to be fairly standard, so it would be a lot quicker to sew the whole sail together, and use batten pockets as well.

    Boom and yard.
    For the boom and yard, I in any case suggest that you avoid using tracks, but rather add hoops at the head and foot of the sail, and then tie the sail on. This lets you adjust  the position of everything, like the halyard’s slingpoint (yard) and topping lifts and lazyjacks etc. on the boom. The recent photo of the JR of my IF clearly shows how things have been assembled.

    Good luck!
    Arne



    Last modified: 30 Jun 2020 12:57 | Anonymous member (Administrator)
  • 29 Jun 2020 22:57
    Reply # 9068480 on 8742744

    I have two comments.

    The first is, that I very much admire your care and workmanship, and your model detail suggests you are making a beautiful job.

    My second comment, though, came to mind when I saw your first post. Why make things so complicated? I was a bit lazy, and impatient to get my sail finished, which was my main reason for skipping the batten pockets and using wooden battens - I just copied what James G. did on River Rat, which was documented in issue 80 (2019) of the JRA Magazine.

    James explained it well, so I quote: " ...I settled on a sandwich type of batten– two lengths of 18x28mm softwood, through-bolted through the head & foot of adjacent panels. The idea being that the two halves, being strongly bolted together, would act as one thicker piece as far as bending forces are concerned. Advantages? No batten pockets to chafe against the mast, wooden battens probably quieter than alloy against the alloy mast, a sail that can be assembled panel by panel never needing the whole sail to be handled with a sewing machine, and a sail where I can change just a single panel if I want to. That last advantage is one I’ve seen others mention, and I’ve also seen scoffed at– when do you ever need to change a panel? ..."

    I found some clean pinus radiata (a cheap soft wood) and ripped it to make 18x28mm batten halves. I did not use bolts, just used those screws with a square hole, and a drill-driver, screws at about 150mm centres, through the sail cloth. Assembling the battens and sail panels was quick and easy. The panels are not sewn together, just sandwiched between the batten halves, a little bit of overlap pierced by the screws. (A seam allowance had been made for that, at the top and bottom of each panel). And lashings at the luff and leech end of each panel.

    And also I did get the benefit alluded to by James. I had made an experimental panel which I later decided to change - and while I was at it, I was also able to correct a mistake in one of the other panels - meaning that I did have to take it all apart and replace a panel. It was quick and easy (using the drill) to disassemble the sail and make the changes.

    As for weight - yes, timber might be a bit heavier than aluminium battens. I too was shocked at the weight of a junk sail. However, it doesn't seem to matter much, in practice. 

    With due respect to James, the method is a bit rough and ready, but it does do the job (for a small sail.) For my next sail, which will be considerably larger, I am planning to use aluminium tube and conventional batten pockets, which is a better way in the long term, I think. Probably more robust, and allows for a little bit of adjustment of tension along the battens.

    Last modified: 29 Jun 2020 23:29 | Anonymous member
  • 29 Jun 2020 16:10
    Reply # 9067567 on 8742744

    A report on my experiences so far.

    Making the battens as proposed was straightforward. But the keder channels hade to be carefully cleaned from excess epoxy before it had cured. I also reamed the channels afterwards using a 10mm drill. (The C.I.Fall company of Eskilstuna Sweden makes a long-hole drill which can be lengthened in 40 cm sections.)

    The picture shows a small prototype section with a 6mm line as filler. I realized that if one uses a single line for both channels of a batten the line forms a loop at the aft end of the batten to be used for fastening sheet blocks. 

    Camber was built into each panel by cutting the sheets to the intended curved shape before attaching the lining. When inserted into the straight keder channels of the battens the panels will have the camber intended.

    Now, when trying to assemble all this into a sail I immediately realized that the sail was quite heavy. The sail area is about 12 sqm, the sailcloth weights 8 kg, and - the battens, made from Swedish pine, weigh totally 16 kg! This makes a sail of 12 sqm area weighing 24 kg. I know that junk rigs are heavier than  other but...

    i have halted the project now for a while to figure out how to proceed. Of course I can  use both a lighter sailcloth and lighter woods. Spruce is lighter that pine but difficult to obtain in knot-free lengths. 

    i would appreciate any comments and suggestions. 

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  • 12 Feb 2020 18:59
    Reply # 8743176 on 8742744

    Nice project. 

    My gunter-rig mainsail of similar size uses this bolt-rope & groove system, I don't think there is any need for the pvc tube, the wooden groove is strong enough. Also, I don't think you need the groove so deep, it can be nearer the surface and your batten will be stronger. I would avoid varnishing or painting the inside of the groove but every season plug the ends and saturate it with linseed oil or a varnish like Le Tonkinois. 

    I'm thinking about a similar system currently but also trying to articulate the battens and get some camber in the sail to keep the experts happy! 



  • 12 Feb 2020 16:20
    Message # 8742744

    Keder, see https://www.jjcarter.com/keder2/what-is-keder is of common use for attaching sails to masts and profiles. I am making a JR for my small swedish open "snipa" (see my profile). The intended sail is a about 11.5 sqm, see "Rigg.pdf".

    The idea is to fasten the panels to battens, boom and yard using keder, see "Lattor.pdf". The battens will be made from two halves of 22 x 45 mm wood (pine) where a 12 mm channel is routed. A 12 x 10 mm GPR tube is glued in this channel. After gluing the two halves together, 2mm saw is used to cut the groove for the keder. All this is simply made using a home shop router and a table saw.

    A prototype panel is shown in the pictures attached.I have not yet found a solution to how to fasten the leech line to the batten ends. I will also make a practical test for the strength of the keder.

    I welcome all comments and suggestions to improvements of this suggested method of making a sail with separate panels. Should i go on?

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