Flat, hinged or cambered?

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  • 12 Nov 2010 21:17
    Message # 461931
    Deleted user
    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 | Deleted user
    Moved from GENERAL FORUM: 19 Aug 2018 19:02
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