Flat, hinged or cambered?

  • 29 Jun 2021 21:50
    Reply # 10712002 on 461931
    Anonymous member (Administrator)

    Martin,
    I regret now that I was so slow with finishing the Chapter 7 about rigging the sail. That chapter was only uploaded in September last year....

    Are you still thinking of changing to hinged battens ?

    Arne

    Last modified: 29 Jun 2021 22:49 | Anonymous member (Administrator)
  • 29 Jun 2021 19:19
    Reply # 10711600 on 10707443
    Anonymous wrote:
    Anonymous wrote:

    As for Martin Simmons(?) and his Taiko, I have no idea. I don’t know his boat and have never been contacted by Martin.

    Arne


     At some point it would seem Martin found your notes Arne.

    "I can say now that If I had read all of Arne Kverneland's published files from the outset it would have saved me much angst." - Martin Simmons

    Quote lifted from his blog here.

    I downloaded, printed and perused most conscientiously The Cambered Panel Junk Rig.

    I then set about building cambered sails of the same dimensions as our flat sails in order to use the same battens and yards. What I did not appreciate was that the loads on the yards would be so great and that aTHP, under enormous tension, would be necessary. Arne’s files that would have saved me angst were his later additions of fixes and improvements. The same could be said of Paul Faye’s account of changing to cambered panels. I remain unhappy with the tension in the upper sections of the sails, though Paul Thompson’s idea of creating drift by moving the standing part of the halyards aft, has ameliorated the problem. It must be said that Taiko is sailing well under her current rig, she is no slouch if she is able to cover a thousand miles in  one week of SE trade wind sailing. Furthermore, there have been no problems with the sails themselves, only running rigging and mast chafing and yard failure.

    More will be written about our experience on our eventual return to NZ.

    Last modified: 29 Jun 2021 19:41 | Anonymous member
  • 29 Jun 2021 13:39
    Reply # 10710714 on 461931

    Mark,

    Yes, you're broadly correct.

    • AR: higher for Weaverbird, a nippy little cruiser/racer; lower for FanShi, a comfortable cruising home.
    • Sending battens from UK to NZ, the maximum length is 3m. Annie needed 5m, so for best economy, for both buying tube and the shipping cost, I elected to send 3m and 2m pieces. Because there is a lot of balance, for ease of handling, the hinge has to be aft rather than forward. What I should have done is bitten the bullet, accepted some wastage and sent all as 2.5m lengths. That would have been better in all respects. Weaverbird has hinges at halfway and further forward, because there is very little balance, the mast needing to be well forward to suit the internal layout. 
    • Don't read too much into the shapes of the upper panels. But the principle factor in the decision making is evening out the changes of direction in the leech, so as to share out the compression evenly.
    • Both luffs are designed straight, however they may look in the photos.
  • 29 Jun 2021 11:16
    Reply # 10710375 on 461931

    …of course I need to buy another boat and stop being an armchair sailor.  Nearly did in the autumn, but then Covid stepped in.  Since been too occupied with renovating a house in the Highlands, making the most of what was left of the skiing, then training hard for the Ben Nevis Ultra in September.  So autumn before I start seriously looking, and always the best time for a bargain. 

  • 29 Jun 2021 11:08
    Reply # 10710359 on 461931

    David,

    Comparing your mk1 Weaverbird rig to Annie’s I see that there are quite a few subtle differences.  (Please correct me if I am not right.)

    • Higher aspect ratio.
    • Hinge point.  Annie’s seems a long way aft.  Though I recall you may have had two hinges.
    • Tapered panels.  Yours don’t change that much from the ones below.  Annie’s much more so.  
    • The hinge point on Annie’s top panel is proportionally further aft.
    • Annie has a concave luff, yours looks straight.

    It would be good to hear your comments, and of course Annie’s. 

    My uneducated thought, would it help if the top panels were not tapered, just shorter?  Accepted it would not look so pretty.

    (Should this be a separate thread?)

    2 files
  • 29 Jun 2021 01:53
    Reply # 10709137 on 10707084
    Anonymous wrote:

    Interesting Paul.

    It would seem to me that the amount of 'drift' from centre of the anchor point would relate directly to the desired yard angle.
    Do you have the numbers on that relationship if it is indeed the case?

    x 'drift' = y yard angle.


    I'm sure there is a relationship but I've never bothered to work it out because many more factors than just yard angle come into play. The drift in general needs to be somewhere between 5% and 10% of the sails chord/yard length. You very quickly find it out empirically when you start to rig the boat.

    You could in fact move the whole slingpoint aft (as I believe Arne does) but I've found that one gets better results by just moving the standing part of the halyard.

    Last modified: 29 Jun 2021 01:55 | Anonymous member
  • 28 Jun 2021 22:03
    Reply # 10708647 on 461931
    Anonymous member (Administrator)

    Discussion in a circle...

    This sort of discussion around the cambered panel sails seems to erupt on irregular basis since the first JRA rally in Stavanger, back in 2004 (See JRA Mag #44). It mostly goes in ring: The cambered Stavanger sails started with being regarded as very baggy (8%)  -  and probably unfit for offshore work. Later, when they started up in New Zealand, and Paul Thompson rigged his La Chica with 10 and 12% camber, the camber of my sails suddenly moved back to being normal and even ‘moderate’ (“Hooray, I am normal!”). Now my sails again seem to move up in the very baggy league  -  still with the same 8% camber.

    Stress in the sailcloth of a cambered panel sail.
    I like to think of the sailcloth I use as being very weak, just as the original Chinese cloth. Instead of beefing it up in the corners, as western sailmakers tend to do, I let the stiff battens, the boltrope, and the Hong Kong parrels act as a stiff frame. This frees the sailcloth from doing any other job than catching the wind and transferring the force from each panel to the surrounding battens and boltropes. Job done. My baggy sails, with no patches anywhere, have proved to work well and last well.

    Stress in the yard, battens and boom.
    When shifting from a flat to a cambered sail in Malena (See NL30), I didn’t anticipate the increased load on the yard, but it proved to be strong enough anyway. Later, with bigger sails, I had to make that yard stronger, in particular in the vertical plane. The longer batten 2 (from top) on Johanna also needed to be made stronger than the others. In Johanna’s rig the THP and YHP also was under quite some load. This has been solved on my last two rigs (Frøken Sørensen and Ingeborg), by increasing halyard drift, shifting the halyard 5% aft of the middle of the yard, and the YHP 2/3 up the yard. Small, simple changes resulting in much reduced tension in the THP and YHP.

    The flat-topped, high-balance sails that many use now, have most probably even lighter loads on the control lines than mine, in particular the SJR. Slieve’s alternative to HK parrels are his very clever batten parrels cum downhauls  -  a real Columbie Egg. Still, my THP and YHP are not anywhere near needing a winch or extra purchase these days, just a moderate tug. In addition, I don’t touch them when under way.

    I wish I could bust this myth about the high stress in the ‘high-peaked’ Johanna sails. Anyway, I stick to it, as it gives the tallest sail on the shortest mast. Handling the stress  -  both in the mast and in the moving bits  -  is a simple matter of engineering.

    Arne

    Last modified: 28 Jun 2021 22:44 | Anonymous member (Administrator)
  • 28 Jun 2021 21:05
    Reply # 10708484 on 461931

    Oh dear, now I have to come back and correct some misleading information! 

    I first used low angled yards and hinges in 1995 on Ivory Gull. Not so very recent (when did Poppy get her first SJR?) 
    I don't think those hinges have given trouble, in ownerships subsequent to mine, and I certainly didn't treat them gently. And no, I do not and have not "heavily criticised" SJR. That's just nonsense. Any design must be able stand up to robust criticism, which is not quite the same thing.  I have let my misgivings about certain aspects of it be known, certainly. I have asked for evidence of successful use on long rough passages (not so far forthcoming), certainly. 

    I sailed Tystie from Canada to NZ with hinges. Those hinges gave no trouble, in a tall sail with a low angled yard. I believe they are still in use.

    I am currently sailing around with hinged battens, well engineered from CFRP and nylon, I do not treat them gently, and they do not give trouble.

    As I have already made clear, I should have made Fanshi's top sheeted batten a size larger, to cope with the greater stress in that position. And now that Annie has made clear where the break was, it is also now clear that I didn't extend the kevlar reinforcement far enough on that batten section. My fault.

    As with all rigs, the design and construction has to be got right. It isn't, quite, on Fanshi, but it can be easily corrected. Arne has agreed that a larger size of batten is generally necessary at the top of the sail. That's really all there is to it.

    To say that a batten is in compression only and can be considered only as a column is, to say the least, misleading. A batten is equally heavily loaded on a broad reach and dead run, when compression due to LHP acting against a component of sheet tension is very much secondary to wind pressure,  as the source of bending loads. I have broken battens under this loading condition. Annie made it clear that the failure occurred the first time she sailed hard to windward, with the HP attached to that batten. So clearly there was some compression in play, and sideways wind loading was secondary at that time. But failure could equally well have occurred on the first hard run.

  • 28 Jun 2021 19:59
    Reply # 10708305 on 461931

    Oh dear, it is not desirable to get involved in these rig design discussions but when misleading information is being offered then it seems a good idea to try to correct a few points.

    This all started because Annie reported a structural failure in her rig in what would appear to be in relatively benign conditions and on a fairly low stressed point of sail which should not raise problems in a well found rig.

    Looking at the posts so far Arne has made the point that by taking some elements of his cambered rig design but not following all the elements then it is probably that the resultant rig will not replicate the consistent performance that his rig achieves. David Tyler states, “The SJR also offers high performance with low stress. It gets it in a different way, but there is still this commonality with my rig: low yard angle, no HPs, just downhauls, and panels that are not so extremely baggy as yours”. This would appear to be suggesting that the SJR is copying from his rig. The expression, “Cart before the horse” comes to mind as initially DT heavily criticized the SJR and it is only in recent years that he has started to adopt the low yard angle downhaul features, but as Arne has commented above, David has not included all the features required to make it a low stress rig.

    In the article 'Some Thoughts' I pointed out that to reduce the stresses in a rig any taper or change of angle of the leeches between panels should be balanced by an equivalent change of angle between the luffs panels. As drawn for Annie's SibLim, the rig has a straight luff from Yard to bottom batten/ boom but has taper in the chord of the top three panels. This means that luff haul parrels are required to push the top battens back against the forward thrust of the leech which places the battens under compression even before there is any wind pressure in the sail. The rig does not simply hang stress free in shape from the halyard as the SJR does.

    Marconi found it necessary to provide stays and spreaders to keep his tall masts in column to prevent bending under the gravitational compression loads, but with battens we do not have that luxury. To withstand compression loads the battens should ideally be kept dead straight and be of a stiff light material. The SibLim rig has hinges in the battens which A) allow the battens to get out of column over their length and therefore suffer bending loads, and B) concentrates these bending loads at high stress points such as the ends of the tubes at the hinges, or the ends of the joining cones in the hinges.

    Unless particularly strongly engineered the battens in the tapered panels with the enforced straight luff are vulnerable to failure, and it would appear that that is what has happened in Annie's case. Hinges battens will always have this weakness when under compression loads, and it is easy to see why Arne stopped using them as soon as he had found another method of introducing the camber required to get respectable performance out of a junk rig.

    A structurally sound junk rig with a torn sail can continue to sail, but a sound sail with a broken structure could be a death trap.

    Voyages have been successfully made with hinges battens, but that does not make them safe. It does not make sense to push your luck and set out with a rig with known weak structural features when the same or better performance can be obtained from rigs with simpler and stronger setups.

    Thank goodness that Annie is an experienced sailor, but even so she found it desirable to resort to engine assistance to get into a safe haven. A less experienced sailor might have made bad press for the JRA if presented with the same situation.

    By the way, the SJR may be thought to be less 'baggy' than Arne's rig, but aerodynamically it is probably more baggy.

    Cheers, Slieve.

  • 28 Jun 2021 19:34
    Reply # 10708251 on 10707491
    Hans-Erik wrote:
    David wrote:

    Martin having succesfully cruised Tystie (flat hinged main, cambered panel mizzen) from NZ to New Caledonia; and now having cruised Taiko (baggy panels) from Mexico to Nuku Hiva and not having enjoyed the rig one little bit, to the extent of talking of scrapping it (new sails, old yards and battens) and asking me what I would make to replace it, to get away from the problems that he's had. And my answer is lower angled yards, hinges, a little bit of barrel camber forward of the hinges, flat sail aft of the hinges.

    By all means check with him first David but it would be great if we could all read the specific issues Martin had with the Arne type sails on Taiko during their Pacific crossing.


    I expect that there's a blog post in preparation detailing the passage and the rig problems reported to me. To avoid any chance of misunderstandings and misinterpretations, I'd rather leave it to Martin to tell it like it is in his own words.

       " ...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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