Flat, hinged or cambered?

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  • 14 Nov 2010 07:11
    Reply # 462643 on 461931
    Having just come to the conclusion that I'd fit a cambered sail to Arion, I read Arne's comments about negative batten stagger in cambered sails (see Arne's pages) and feel less happy.  True, he found some solutions but I find myself thinking about hinged battens again, or maybe even a flat sail (Maybe I'll join the flat earth society!).  Presumably with hinged battens the sail will still behave like a flat sail.  That predictable, "fully automatic" behaviour (To use Hasler's term) means more to me than windward performance.  I have sailed the Pacific on an engineless gaff schooner with baggy, hand-sewn canvas sails and that boat did not go to windward, I can tell you!  I have sailed unweatherly, engineless boats much of my life, sidling up to harbours like a square-rigger - it requires patience and forethought but is perfectly doable.  It would be nice to have some lively performance but not if the price is too high, and I'm not talking dollars.  I wonder though, perhaps David has something to say here, if the use of multiple luff hauling parrels on a cambered sail will let you force the battens aft, assuming you drop the sail panel by panel, tensioning the parrels as you go?  And I also wonder, is my assumption that a flat sail with hinged battens will still behave like a standard flat sail correct?  Some days I feel like a kid on his first day at school with this junk rig business! 
  • 13 Nov 2010 12:15
    Reply # 462208 on 461931
    Anonymous member (Administrator)

    Stavanger, Saturday.

    Brian,

    As you soon will understand, I and David have a bit different view on some of your questions:

    About the need for camber David and I fully agree.

    The same goes for controlling the yard with a combination of running yard parrel and luff parrel.

    However, we have different view on the Hong Kong parrels. I find them to be fully adequate in restoring the diagonal stiffness in the cambered batten panels. It takes a bit fiddling to get them right after rigging the sail, but after that I mainly forget about them. Maybe David’s use of luff hauling parrels will ensure even better setting, but as long as the Hong Kong parrels prevent big, diagonal, camber-robbing creases to develop, I am happy.

    I use only 4 running lines in my sails; sheet, halyard, yard h. parrel and one (upper) luff hauling parrel. If I were to fit another one, I would either fit one or two light down-hauls to let the lowest luff set better (see private photos with comments under my profile), or I would fit a yard fan-up preventer for offshore use.

    As for what is the right camber, 4, 6, 8 or 10%, I feel that there is no "right " number; it depends on the boat type. I would give a heavy, under-rigged boat much camber, say 8-12%, while on a light flyer, say a trimaran I might aim for 4 – 6%.

    Of course, the top panels must be made flatter than the lower panels.

    If you look at the photo review from the Norwegian JRA rally in Stavanger this year, you will find that all the parallelogram panels shown are around 8% with the exception of Samson’s foresail which is 10%. Samson performs exceptionally well considering her low SA/disp of only 13.2.

    I suggest you go to YouTube and search for "Norwegian Junk Rig Rally". There you will see them live.

    Conclusion.

    Rig your boat with cambered panel sails. Then try it with both the multiple luff hauling parrel method and then with Hong Kong parrels. Finally report back to us!

    Good luck!

    Arne

    Last modified: 13 Nov 2010 12:15 | Anonymous member (Administrator)
  • 13 Nov 2010 04:58
    Reply # 462115 on 461931
    Brian Kerslake wrote:


    I fancy cambered, but there are some questions:




    Hello Brian,
        Welcome to the website, and thanks for putting Paradox on the map - I wish more people would. One question - you've put her into HM Prison on Portland!! have you taken up residence there as well? She just needs dragging northwards a bit into the marina.
       Thanks for posting all these interesting questions. Where do I start?
       On all junk rigs, the yard is trying to rotate so as to lower the peak and push the throat forward, tending to crease the panels diagonally. This is true in the upper panels of a flat, Hasler sail, but it is easily remedied with tension on the luff parrel. It is equally true on a sail with cambered panels, but it shows up more if it is not remedied. It shows up more further down the sail, because each panel does not have the diagonal stability of a flat panel. The problem gets worse, the higher-peaked the design of the sail - a Van Loan sail is easy to deal with, since applying a little luff tension will readily pull down the throat. A very high-peaked sail cannot be controlled by luff tension, since luff tension has little effect on controlling the rotation of the yard.
       The essential thing is to have a yard parrel and upper luff parrel that effectively work together to peak up the yard. If the yard parrel is attached to the yard, not at the halyard attachment point, but further up, as near to the masthead as possible; and if the end of the upper luff parrel is attached, not to a batten, but to the heel of the yard, then you are getting the best possible control over the angle of the yard.
       I have never liked Hong Kong parrels. You can only get them absolutely right for one set of circumstances, and they are at best a compromise at other times. I much prefer to use a second luff parrel to control the middle of the sail. It pulls the sail down, into the mast and aft all at the same time, and after some experimentation in how to rig it, can provide effective control over diagonal creasing in the middle panels. I go further, and say that a lower batten parrel, to the lowest battens, is similarly effective. With three batten parrels, you have lines that can act as downhauls for all battens, as well as acting as sail shaping aids.
       To give an example: I made cambered panel sails for Badger in 2006, but left to go voyaging before they were rigged. A week ago, I visited Alan and Gloria Parsons, who told me that Badger's performance was greatly improved compared with that obtained with the old flat sails, and that using upper and middle luff parrels did allow them to shape the sail effectively without diagonal creases; but that they had to work a little more at achieving a good result than they did with flat sails.
       High or low aspect ratio won't have a great deal of influence - it's the control over the yard angle that matters more.
       A mast that bends unduly is what throws the fixed Hong Kong parrels out of kilter most, and there's no answer, except to use an adjustable system - luff parrels.
       Gravity doesn't have much effect on the tubular battens you'll be using, they're too light. The answer? a set of luff parrels.
       All the problems in setting cambered panels well increase with the amount of camber built in. For this reason, I advise those not looking for the ultimate performance not to get too carried away when putting in the camber. 6% is enough to get good performance, without looking excessively droopy when the wind doesn't blow.
       I met a Freedom 39 in Stornaway, years ago, and thought it a nice-looking vessel, but the owner was complaining of lack of windward performance. I suspect that it was because of the large carbon masts in front of the bermudan sails destroying their effectiveness. I don't think you'll notice much loss of performance compared with your present rig if you go for a  good cambered panel rig. You'll do a little more string-pulling than with a flat sail, but not much more. You might actually get to enjoy the feeling of going to windward well!
      
    Last modified: 13 Nov 2010 04:58 | Anonymous member
  • 12 Nov 2010 21:17
    Message # 461931
    The attractions of the junk rig when I first came across it (1980 when I beat round an anchored British destroyer off Episkopi, Cyprus thinking 'there has to be an easier way to get this sail down') were it's simplicity (flat), ease of setting, sheeting and reefing, and its relatively low cost. Three flat junk sails later (Kingfisher 20+ and Sunbird 32 schooner) my wife and I are converting our Freedom 39 schooner to junk, and are wondering what style of junk sails to use. Well that's not quite true as we've asked Sunbird to come up with a design and it looks as if we'll then choose cambered, but there's still time to reconsider.

    As one of my recent email correspondents has pointed out, anyone who can haul up and pull in a flat sail could perhaps achieve 95% of its potential performance, and that could be maintained with little effort or attention. In pursuit of an improvement to windward, however, we now have 'solutions' (cambered and/or hinged and wing) which are more expensive, more complicated, perhaps more difficult to set to achieve their full potential, and perhaps more vulnerable to damage and more difficult to repair. Whatever happened to the KISS principle (Keep It Simple, Stupid)?

    We're discounting hinged battens which we reckon would be OK for coastal work but not for occasional longish offshore passages. My wife fancies flat, because we're used to that and we think they look better than the few cambered sails we've seen for real which, in no-win, no-wind situations, can look like laundry on a line. (I know, we can always drop them.)

    I fancy cambered, but there are some questions:

    It seems there can be problems with creasing. Should the upper panels be cut as close to triangular as possible (like Arne's) in an attempt to minimise the risk of creasing? Are the lower panels best controlled with Hong Kong parrels or with a running luff parrel or parrels?

    Our Freedom 39 has very tall masts (see picture link from the location map, taken in Brighton marina's inner harbour). If we go for cambered, will working to keep the aspect ratio low-ish (e.g. by hanging the sails low or arranging 'false mast-tops' a bit down from the top of each mast, not by chopping them), help make it easier to set the sails and keep them set?

    Is a taut luff - tight tackline to the deck, opposing the halliard - essential to form the datum for the luff of the rectangle of the lower panels, and if so how do we preserve that? Given a steady boat on a steady course and heel and a steady wind, I've seen that each panel can be made to give a close approximation to an aeroplane's wing; however, the boat, course, heel and wind are not steady, so when one or more of those alters, as it/they will, the carefully achieved setting of the panels may be lost.

    There's also the problem of flexible carbon fibre masts on our Freedom.  I don't yet know how much they bend, but when the wind changes they will bend more and so the tension in the luff could be lost and hence the set of the panels. Would (hypothetical, this) non-tapered masts give a better result with cambered panels? And if so, how do we get round that - Hong Kong parrels again?

    Finally, there can be no tension (other than that induced by gravity) in the luff when the sails are reefed, even by one panel, unless we add down-hauls. We don't really want to do that, being used to the simple controls of flat sails. So is gravity enough?

    All ideas/thoughts/comments welcome.

    Congratulations on a great new site!


    Last modified: 12 Nov 2010 21:17 | Anonymous member
    Moved from GENERAL FORUM: 19 Aug 2018 19:02
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