Flat, hinged or cambered?

  • 20 Aug 2018 17:48
    Reply # 6584297 on 461931

    Flat? Yes (the sailcloth).  Hinged? No.  Cambered? Yes

    Being just from a fjord sailing guy, my words have limited weight, but I just feel tempted to jump into the thread and mention one way to make a cambered sail where I combine the advantage of a “flat sewn” sailcloth with the advantage of no hinges in the battens.

    Instead of using hinges I have curved (bent) my battens permanently, thus the batten provides camber while being in one piece structurally.  The battens flip a half turn “around themselves” when I tack.  However, to make this work, I have made “swivels” at each batten end and also a swivel at the aft end of the batten parrel.  With these in place, the canvas does not wind up on the batten and also the batten parrel does not get wound up on the batten when the batten rotates the half turn.  You may well say that this isn’t simpler than hinges as I have made those other moving parts instead, but on the positive side the swivels are “low stress” parts compared to the hinges.  

    So what makes the battens turn?  Simply the wind force on the sail, but they need a little help when there is almost no wind. I am thinking of making a video showing how the battens rotate the half turn when I tack, but I now have an ugly tarp sailcloth and would like to make a new and nicer sailcloth first, so it will maybe happen next year.

    Cheers 

    Nils

    Last modified: 20 Aug 2018 18:02 | Anonymous member
  • 17 Aug 2018 09:57
    Reply # 6579244 on 461931
    Anonymous member (Administrator)

    Annie,

    The sail of Fantail is quite different from Johanna’s and Ingeborg’s sails. It looks more like the original all-fanned sails in Hong Kong. These were an extreme case of low aspect ratio and un-balanced sails. However, they managed by making the battens really stout, and relying mostly(?) on the highly loaded HK-parrels for making the sails set well. This let them set the biggest possible sail on the shortest (cheapest) mast.

    This is not needed on the HM-sails, where the majority of panels are parallel. As said, with ample mast height, (and by increasing the sail’s balance a bit) the geometries can be made to ease the forces on the THP and YHP. I still keep the HKP, but the load on these is not nearly enough to bend any batten.

    I guess a most important factor here is that the THP and YHP need no adjustment during sailing, except when reefing and un-reefing. I don't expect to be able to harden in the YHP while sailing fully close-hauled at full speed. With light forces, I mean either when off the wind or with the sheet slack.

    Arne



    Last modified: 17 Aug 2018 16:54 | Anonymous member (Administrator)
  • 17 Aug 2018 09:25
    Reply # 6579208 on 461931
    Anonymous member (Administrator)

    You could well be right, David, but I am not convinced. As for looks  -  the hinges don’t look bad inside batten pockets. Besides, I was talking of all-aluminium hinges (better make the plug in the middle of aluminium too). My battens and hinges on Malena were round, so could swing in any directions. No hinge pins needed. After 2-3 seasons of use, there were no signs at all that the sharp edges (which had been rounded with a file) on the battens and hinges had chewed on each other. This came as a surprise to me. I don’t have x-ray eyes so cannot tell if the batten pockets were worn inside, but I doubt it, since the hinges didn’t move around.

    Now I see Annie is bringing in the word ‘Fiji’ here. That makes a big difference from the coastal cruising I was thinking of. Even better reason for dropping the hinges entirely. There should be no reason why her planned sail could not be made with conventional camber. Hinges are simply not needed.

    Arne


  • 17 Aug 2018 09:18
    Reply # 6579207 on 461931
    Well, my entry into this discussion came before you mentioned the fact that by moving the sling point and the YHP, you now have very light loadings on your lines, Arne.  I absolutely hated the amount of force I needed on my LHP on Fantail.  And I've felt the same watching David on Footprints and Alan on Zebedee.  I just don't want to go there again, and I am looking for a way around it.  Yes, just camber would be fine, but only if I can be sure that the lines will need no more than a slight pull to set the sail nicely.

    I am not good at experimenting with setting a sail: I don't have the sort of mind that can see that if I move this line to here and then attach that line there, then this will happen, so i need to follow other people's leads on this.  I want a sail that will perform well so that I don't need to motor.  I may not go to Fiji - I need a big dose of self-confidence first - but I'm trying to build the boat capable of so-doing, so therefore the sail needs to be up to it, too.

    But it's only 1,000 miles to Fiji - and if I decided to sail to Stewart I at the bottom end of NZ, I'd be sailing the same distance, so it's relevant, anyway.


  • 17 Aug 2018 09:05
    Reply # 6579203 on 461931

    The hinges in Weaverbird's battens, made from nylon 66 - simple, robust, do not chafe the sail or fret the batten tubes, proven over 3000 miles.

  • 17 Aug 2018 08:25
    Reply # 6579169 on 461931

    No, Arne! Just - no. 

    Annie is doing everything she can to make SibLim a beautiful boat. These hinges just aren't in the right league.

    These are the hinges that eat into the sail, long term. I remember Pete Hill rolling his up in canvas strips before starting the Jester Challenge in Shanti. They made a little more sense with his wooden battens than they do with tubular battens, though there's no getting away from this disadvantage.

    The line contact at the ends of the middle piece is bad engineering. It's the same situation as with Tystie's first set of GRP wingsail battens - long term, the edge chafes and frets a deep groove into the batten tube, due to slight vertical movement. It's one of the reasons that I decided to put these battens into retirement.

    Note that the key words are "long term". Just how many sea miles did you do with these hinges, I wonder?

  • 16 Aug 2018 09:50
    Reply # 6576513 on 461931
    Anonymous member (Administrator)

    Annie

    if you have to use batten hinges (no one has to do that), then I would rather recommend these 'outside hinges (on aluminium battens). They may look crude, but from an engineer's point of view, these will always be stronger than 'inside' hinges. Any one with a hacksaw, a file, a drill and a bit hardwood and glue can make this thing. It is basically a variation of the hinges I made for Malena in '91. They held up well. To avoid black stain from the aluminium, I guess painting in two-pot paint will do the trick.

    Arne 


    Last modified: 16 Aug 2018 11:36 | Anonymous member (Administrator)
  • 16 Aug 2018 09:18
    Reply # 6576504 on 6576377
    David wrote: As the longest piece of batten is only 2.5 metres, it wouldn't be impossible for me to get 38mm high quality GRP tubes from the supplier that I use, make up the battens and hinges, and send them downto NZ.
    'Strewth, what an offer.  I need to think about this.  The darling wee boat has to go very respectably to windward, otherwise everyone will think I've trashed your design.  And I might not get to the islands ...  On the other hand, as you appear to think that Weaverbird sails adequately, then I assume you feel the concept will work on Siblim.

    The fibreglass battens I bought here were bloody useless and I loathe alloy ones, to be honest, but yours from the UK, complete with hinges, sound like an investment worth making. Will you be able to take the time out from making your new wing sail, though?

    (BTW, I did mention that Badger's sails were HAR.)

  • 16 Aug 2018 08:07
    Reply # 6576466 on 6575572
    Anonymous
    David Tyler wrote:
    Arne wrote:

    Webmaster,
    Are you sure this belongs in the General Forum and not in the Technical Forum?

    Arne

    I agree, this is very much a technical topic.

    David and Arne,

    I agree that it could fit into the Technical Forum, within the description of:

    discuss matters to do with improving the junk and related rigs

    But, referring back to the original questions on both topics, I chose to put it in the general forum with reference to:

    request advice on choosing and using a junk rig

    To my (admittedly pedantic) eye, the use of 'a' instead of 'the' suggested this as the best place for what is essentially a discussion of which variety of junk rig to use.

    However, either Forum will work, and if you both still feel it should be in the Technical Forum, I can easily move it across.  As two of our most prolific posters, you have a good 'feel' for what fits where.

    Mark

  • 16 Aug 2018 06:34
    Reply # 6576377 on 6575734
    Annie wrote:
    David wrote:On my mini lathe, I just have enough capacity to turn hinges for 38mm tube.


    Having managed to bend 38mm T6 battens on Fantail, I'm think if I were going for alloy, I'd have to go larger on SibLim.  So that puts the kibosh on that idea.  Back to shelf foot!
    As the longest piece of batten is only 2.5 metres, it wouldn't be impossible for me to get 38mm high quality GRP tubes from the supplier that I use, make up the battens and hinges, and send them downto NZ.
    Last modified: 16 Aug 2018 06:34 | Anonymous member
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