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Cambered panel sails on Wild Fox

  • 15 Dec 2011 03:44
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    Reply # 773759 on 770677
    Anonymous member
    A very good read Arne, thank you.
  • 14 Dec 2011 20:44
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    Reply # 773407 on 773391
    Anonymous member
    Arne Kverneland wrote:

    Stavanger, Wednesday

    I’ve tried to sort out my thoughts on what may cause the stressed

    battens when using cambered panels. Here is a little write-up I just put

    together:

    http://dl.dropbox.com/u/49284570/Arne%20Kverneland

    %27s%20Junk%20Rig%20Files/20111214%20Peaking%20up

    %20the%20junk%20sail%2C%20ver%2020111214b.pdf

    I hope some of it makes sense

    Arne

    Good work, Arne!
    That's a very clear explanation of the forces at work, and I agree with all that you say.
    Last modified: 14 Dec 2011 20:45 | Anonymous member
  • 14 Dec 2011 20:19
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    Reply # 773391 on 770677
    Anonymous member (Administrator)

    Stavanger, Wednesday

    I’ve tried to sort out my thoughts on what may cause the stressed

    battens when using cambered panels. Here is a little write-up I just put

    together

    I just put it in my Dropbox folder first, where it easy to update.

    Later (..when I re-learn how...) I will put it under Arne K...’s Files

    in the public section of this site.

    I hope some of it makes sense

    Arne

    PS: Thanks to Annie  Hill and David Tyler for feedback on my draft.

    Last modified: 01 Feb 2015 11:14 | Anonymous member (Administrator)
  • 12 Dec 2011 12:01
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    Reply # 771610 on 770930
    Anonymous member
    Gary King wrote:I wonder what kind of battens on Wild Fox. Great looking boat btw.

    We will still go for cambered sails, (our boat is definitely going offshore). Probably 50mm diameter aluminium battens on the 30sqm & 22sqm sails.

    edit added:
    Appears that with flat panels, the sail fabric takes much of the load to maintain shape. Cambered panels move all the load to the battens, so maybe the battens need a doubling in strength in such a case (?).
    The original battens were laminated sitka spruce and things of great beauty.  Pity they didn't work.  The new battens are fibre glass and a much smaller section.  They are horrible to look at but as they are in the sail cannot be seen...
  • 12 Dec 2011 09:30
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    Reply # 771572 on 770677
    Anonymous member

    Looking at the photo of Wild Fox and the one of Badger two rows below and you may notice that Badger seems to have two similar chord sails on the two masts, whereas Wild Fox has a smaller foresail and much larger and wider chord sail aft. The centre of area of the two rigs will be very different if the masts are in the same positions.

    Looking at the shape of the shelf foot panels in the aft sail on Wild Fox and it would appear that the camber has been carried quite far aft in the sail unlike Badger where David has a flat run from about the mid point and this would also suggest that the 'Fox will have more weather helm.

    Assuming Badger is nicely balanced then these two observations alone would suggest that 'Fox would be hard mouthed. If I am right about these two points then the easiest fix might be to put a nice split rig on the foremast. OK, I know, I'm biased.

    Cheers, Slieve.
  • 12 Dec 2011 00:26
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    Reply # 771208 on 771185
    Anonymous member
    Slieve McGalliard wrote:

    David, when I click on Arne's sketch I get the Access Denied message just the same as when I click on View Profile. There's something funny going on.

    I find this thread about cambered sails not being suitable for offshore sails rather worrying amd think that it is wrong to push opinions based on a couple of individual cases. There seems to be evidence that rigs are being built with high stress areas and without adequate structural strength to accomodate the stresses. The choice is to either beef up the structure or reduce the stresses, or a combination of both. When I modelled my rig I made it as stress free as possible and arranged the curved luffs to balanced the curved leeches. 

    There is no reason why a cambered sail should not be used offshore.

    Cheers, Slieve.

    Nobody is saying that cambered panel sails are unsuitable for offshore use, Slieve. I'm simply reporting the findings of two members who  are dissatisfied, and we are suggesting ways in which their rigs could be improved so that they become satisfied. 
    I myself would choose a cambered panel two-masted rig without hesitation, if I were to have a rush of blood to the head and re-rig Tystie (unless I were to whip the mizzen mast out and put a larger version of Fantail's sail on - but that's another story).  
    But it has to be designed right, built right and rigged right, that's what we're saying.
    I can't see any evidence that rigs are being built with high stress areas - apart from those HK parrels, which do put loadings onto the battens that weren't there before. I can only see evidence that high aspect ratio, cambered panel rigs have been built without arranging the parrels (all the parrels) in such a way as to set the sails well. 
    I agree with you about the curved luff, as I've said before. It's worth incorporating.
  • 12 Dec 2011 00:03
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    Reply # 771186 on 770677
    Anonymous member
    Another note from Anthony:

    My LHP goes through every batten. I have tried different combinations and this seems to work best. I met people who are building a 37.5 for someone else and they are talking to Jay about changing the sail plan to make it more equal. I will be very interested in the results but they will be academic as I am stuck with what I have got. They have a 34 and sail a lot under foresail alone


    From F4 up with the wind behind foresail alone it is otherwise the boat will not self steer. If I put enough bias in the rudder to counteract the weather helm then if the wind eases the boat goes into a gybe. Not good!

    I wonder whether the poor steering that Antony reports is due to having too much weight forward, and being bows down?

    Pete and Annie liked to sail Badger downwind under mainsail, with the foresail amidships, but this could be a simple case of "different folks, different strokes". Also, the Benford dories may well have differing keels, rudders and weight distribution, all of which will affect the steering.

    Just looking at the photo of Wild Fox, I'd want to try a "throat hauling parrel" attached to the yard, then through blocks on the second and third battens down, as my starting point for curing the diagonal creases. But from thousands of miles away, and without having sailed on Wild Fox, that's pure armchair theorising.
  • 12 Dec 2011 00:02
    Quote
    Reply # 771185 on 770677
    Anonymous member

    David, when I click on Arne's sketch I get the Access Denied message just the same as when I click on View Profile. There's something funny going on.

    I find this thread about cambered sails not being suitable for offshore sails rather worrying amd think that it is wrong to push opinions based on a couple of individual cases. There seems to be evidence that rigs are being built with high stress areas and without adequate structural strength to accomodate the stresses. The choice is to either beef up the structure or reduce the stresses, or a combination of both. When I modelled my rig I made it as stress free as possible and arranged the curved luffs to balanced the curved leeches. There is no real stress on the battens other than to keep the luff and leech apart. There is no reason why a similar method should not be used with any other rig. I didn't allow enough for the downward pull of the sheet when close hauled on Poppy's rig, but have been working on a yard peaking halyard/ parrel to balance the sheet loads for some time.

    In October I sent a sketch of a 'yard peaking parrel' to a friend who has built a split rig and should be sailing very soon, and am looking forward to hearing how it works. I don't seem to be able to insert it into this text. It's different to Arne's sketch in that a line runs from the throat of the yard, round the mast and back to the throat, but then I ran the hauling line up the yard to a block on the yard just behind the mast so that the line running down to the deck would not distort the important jib camber. It is only attached to the yard. It should have the same effect as Arne's sketch and should control the yard well in lumpy conditions. The rest of my rig simply hangs from the yard, and is held firmly in place by the downhaul/ batten parrels.

    There is no reason why a cambered sail should not be used offshore.

    Cheers, Slieve.
  • 11 Dec 2011 18:48
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    Reply # 771077 on 770677
    Anonymous member
    The key is to make the upper luff hauling parrel as effective as possible. I, like Arne, tend to think of it as " the line that peaks up the yard" rather than "the line that pulls the luff back", and would agree that "throat hauling parrel" would be a more accurate name for it.
    The ways to make it more effective include:
    • Attaching the upper end of it to the lower yard end
    • Extending the yard downwards by a small amount
    • Extending the batten ends that it controls by a small amount
    • Adopting a planform with a low yard angle (eg, Van Loan) that naturally puts the yard and batten ends further forward from the mast.
    The convex luff (which I'm going to consider as a permanent feature in any future designs that I do, I like it so much) helps in a different way. So long as there is some camber in the panels, luff tension tends to straighten the luff, which tends to pull the battens in the centre of the sail backwards as a middle luff parrel would do - but gently and evenly, unlike the action of a middle luff parrel.  
  • 11 Dec 2011 17:39
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    Reply # 771046 on 770677
    Anonymous member
    All I can say is that Carl Bosteck's Aphrodite which has a cambered schooner rig (van Loan style sails, rig designed and sails made by myself) sails well and balances to near perfection. I used a combination of Hong Kong parrels and LHP's. It's early days for this boat and there is still lot's of room for tweaking and further development but so far so good.

    Aphrodite sets approximately 1300 ft sq on two sails of roughly equal area. The battens are substantial being 50x50x3 square section with well rounded corners, There has been no sign of the battens bending.
    Last modified: 11 Dec 2011 19:55 | Anonymous member
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