The Weaverbird planform: scaling up, or down

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  • 09 Feb 2017 23:40
    Reply # 4601383 on 4601328
    Arne Kverneland wrote:
    David Tyler wrote: The fit of the sail to the battens has to be snug enough that the hinges don't try to separate. Last year, I overdid it and put on too much tension, which I think is what Erik is seeing - horizontal creases, not vertical wrinkles due to slackness. This year, I've not tensioned the sail so much, and we'll see whether there are less creases - when the weather warms up enough to rig the sail and try it out.

    David,
    would it be possible to drill a hole through the hinges to let a line through? These days, with very strong Dyneema rope, the hole should not need to be  more than 2-3mm wide. When I used hinges, I found that internal line to be extremely useful, in several ways (JRA NL 24):

    • It kept the battens together, without any need to tension the sail along them.
    • It ensured that no bits would fall over board when installing and retrieving.
    • It let one store a folded spare batten in a locker or under a berth, ready to be erected and passed into the batten pocket.
    Arne
    Yes, I do exactly that, but at present, I confine it to the two hinges and the middle piece of the batten - it makes it easier to assemble a batten, and avoids dropping pieces overboard if a batten has to come out at sea. It's a difficult machining job to drill along the axis, but easy to drill across the hinge through the central flange. The hole needs to be 5mm diameter to accept a 3mm cord, and Dyneema isn't necessary, polyester is good enough.

    Again, I put on too much tension last year, because I was nervous about separation, but this year, I will go for no tension, no slackness - just a neutral fit that should produce minimum wrinkles and creases.

  • 09 Feb 2017 22:34
    Reply # 4601328 on 4598653
    Anonymous member (Administrator)
    David Tyler wrote: The fit of the sail to the battens has to be snug enough that the hinges don't try to separate. Last year, I overdid it and put on too much tension, which I think is what Erik is seeing - horizontal creases, not vertical wrinkles due to slackness. This year, I've not tensioned the sail so much, and we'll see whether there are less creases - when the weather warms up enough to rig the sail and try it out.

    David,
    would it be possible to drill a hole through the hinges to let a line through? These days, with very strong Dyneema rope, the hole should not need to be  more than 2-3mm wide. When I used hinges, I found that internal line to be extremely useful, in several ways (JRA NL 24):

    • It kept the battens together, without any need to tension the sail along them.
    • It ensured that no bits would fall over board when installing and retieving.
    • It let one store a folded spare batten in a locker or under a berth, ready to be erected and passed into the batten pocket.
    Arne
    Last modified: 09 Feb 2017 22:42 | Anonymous member (Administrator)
  • 09 Feb 2017 22:22
    Reply # 4601314 on 4464371

    Actually, both sheets go down to the cockpit sole, where the block for the bermudan mainsail sheet was secured. I have an Easy Marine block which permits the tails of two sheets to exit parallel, and close to each other, through a double jammer. The lower sheet is a single part, connected to the lower span. The upper sheet is a 3:1, with its bitter end connected to the middle span, from where it leads through the cross sheave on the Easy Marine block, up to a block on the upper span, then down to the final sheave and out through the jammer.

  • 09 Feb 2017 22:05
    Reply # 4601291 on 4464371

    David I'm not quite understanding your sheeting arrangement, the uploaded photos aren't clear (probably will be in retrospect). The drawing seems unusual, with one sheet set blocked to the transom and the lower span seeming to go to the center of the cockpit. If I recall correctly you prefer 2 separate sheets for your main. In the photos it looks like they all go to the aft end of the cabin roof? 

    I'm walking myself through the photos as I write this: Upper span 2 part ( sheetlet to battens 2,3), center span single part (to batten 4 only, no sheetlets), lower span single part (sheetlet to 5,6 ).

    Love to see a bit more photo detail on the sheeting arrangement in your cockpit. 

    Good luck with the rudder rebuild, I'm still hoping to write up my rudder rebuild from last year styled after Arne's ideas and LaChica's rebuild, very successful improvement to performance. 

  • 08 Feb 2017 20:02
    Reply # 4598653 on 4598092
    Phil Brown wrote:
    David Tyler wrote:

    The wrinkles in Weaverbird's sail are mainly due to the fact that I thought that I could use 2D barrel camber as the amount of rounding was small. I will never again use plain, flat barrel camber.

    Does having tension in the panel along a batten adversely affect hinged battens? Slightly stretching the 2D barrel cut panels along the battens on Brenda B seems to eliminate large wrinkles with only a minimal affect on camber, I believe. 

    These pics from my album were taken on one of my first outings with the new sail while still making adjustments to sheeting etc. The telltale on p6 would be flying, except that I stitched it to to the leech's webbing. 

       

    The fit of the sail to the battens has to be snug enough that the hinges don't try to separate. Last year, I overdid it and put on too much tension, which I think is what Erik is seeing - horizontal creases, not vertical wrinkles due to slackness. This year, I've not tensioned the sail so much, and we'll see whether there are less creases - when the weather warms up enough to rig the sail and try it out.
  • 08 Feb 2017 16:32
    Reply # 4598092 on 4597266
    David Tyler wrote:

    The wrinkles in Weaverbird's sail are mainly due to the fact that I thought that I could use 2D barrel camber as the amount of rounding was small. I will never again use plain, flat barrel camber.

    Does having tension in the panel along a batten adversely affect hinged battens? Slightly stretching the 2D barrel cut panels along the battens on Brenda B seems to eliminate large wrinkles with only a minimal affect on camber, I believe. 

    These pics from my album were taken on one of my first outings with the new sail while still making adjustments to sheeting etc. The telltale on p6 would be flying, except that I stitched it to to the leech's webbing. 

       

  • 08 Feb 2017 08:23
    Reply # 4597266 on 4464371

    Erik: 

    Light(er) battens and cloth: My new battens are a little heavier, and a lot stronger and stiffer. Still, I will be using spanned downhauls - a downhaul for battens 2 and 3, a downhaul for battens 4 and 5. I was using short batten parrels last year, and these did inhibit free fall when the halyard was eased. This year, I will have semi-short batten parrels in the lower sail, but still a short batten parrel for the top batten, in an effort to avoid the need for a LHP. I'll report back when I've had a sailing trial. I suspect that a larger version of this sail should use a LHP, to keep friction within reasonable limits.

    The wrinkles in Weaverbird's sail are mainly due to the fact that I thought that I could use 2D barrel camber as the amount of rounding was small. I will never again use plain, flat barrel camber. It's well worth taking an extra half an hour to put in some tucks or broad seam to make a 3D shape - and that applies to unhinged battens as well as hinged battens. This isn't a question of it being easier for an unskilled sailmaker to make 2D barrel camber, it's a question of putting in a little extra time and effort to make a sail that sets well.

    Scale factor: Who knows? I don't. 

    Hinges: one important lesson I learned from my attempts at wingsails is that constraining hinges to less than equal articulation in all directions is a disaster. The batten simply rotates about its axis so that it can articulate in the direction it finds easiest.

  • 08 Feb 2017 06:23
    Reply # 4597169 on 4464371

    David:  Thanks for the points to ponder.

    Light(er) battens and cloth - is there a risk, as the weight of the cloth and battens get lighter, that the sail will not set with the proper luff tension or reef by itself.  I seem to recall some people using the equivalent of a cunningham (smart pig?) to put tension on the lower panels and help the sail drop.  You are moving to stiffer battens but are they lighter?

    Weaverbird - I've studied the pictures of Weaverbird under sail and as we had previously discussed, there were some wrinkles in the panels that may be due to low tension along the batten pockets.  I noticed that the wrinkles are along the upper edge of the panels only and more confined to the area of the hinges, i.e where the most "sag" may be expected.  The back back half of the sail has little to no wrinkles and in this area the sailcloth cut is flat.  

    Asymmetric panel edges - I've then tried to think through what would happen if the curve on the upper edge of the panel is made flatter - this may take out the excess cloth when the winds are light, and reduce the camber along the lower edge of the panel above as it does if both edges are symmetrical.  And when the wind increase, the rise of the batten would flatted sail along the upper edge the lower panel and increase the camber along the lower edge of the upper panel. Net zero sum?  Maybe an OK characteristic or is leaving/living with the wrinkles better?  No answer expected :)


    Scale - A concern I have is what happens when the sail is scaled up and the battens are heavier and more cloth is used for the camber.  The expectation is that the total deflection of the battens "sag" gets larger, but is it effectively the same as for a smaller sail and will the battens "lift" in similar conditions, or is there a amplification of that occurs as the sail is made larger?


    Hinges - If the hinges are constrained to articulate  within the horizontal plane only... is that a bad idea?

    Erik


  • 07 Feb 2017 08:21
    Reply # 4595548 on 4464371

    You're right, of course, Erik. There must be some tendency to sag in light airs, as the battens must weigh something. Equally, deeply cambered panels can look very saggy and unsightly in light airs. In both cases, the less the weight, the less breeze it will take to lift the sail into shape. I don't see a problem if the wind is over 5 knots, and below that, I tend to the view that an infernal combustion engine will do a better job of moving the boat along, much as I dislike them.

    I do use light tubes for the battens, though my sailcloth is rather heavier than it needs to be. Much will depend on the weights of each that you choose. 

    There may be an argument for using a different curvature on the upper and lower edges on the panels, but if so, I haven't thought through which edge should be more curved. Should the lower edge be curved less, so as to support the batten better, or curved more, so as to let the batten sag to its fullest extent and still have enough cloth to put in the camber? Should the upper edge be curved less, to avoid an excess of material in the top of the panel as the batten sags? I don't know.

    I'd better come clean here, and admit that I've been upgrading my battens over the winter. Last year, they were 30mm diameter GRP, except for the top sheeted batten, which was 38mm GRP. They seemed to be strong enough, but rather more flexible than I liked. I've invested in some 38mm carbon fibre tubes, using them for the middle and after sections of all battens and re-using the existing 38mm GRP tubes for the forward sections, where the greater weight is not too harmful, and will help the sail to come down readily. The 38mm carbon is only marginally heavier than the 30mm GRP, and of course much stronger and stiffer. I don't suggest that carbon is necessary to make successful hinged battens, only that lighter, stiffer, stronger battens must be better than the reverse.

  • 07 Feb 2017 07:20
    Reply # 4595460 on 4464371

    David - as I am designing the rig for our Freedom 40 -  really copying yours- I've come to give the hinges some thought.  It occurred to me that I don't fully understand how they work in combination with the camber in the sail...

    On a junk sail that only uses the hinged battens for inducing camber, the battens are supported along their entire length by the taut cloth.  And if the design relies on the cut of the sailcloth for camber, the battens themselves are not hinged and therefore self-supporting.  Since there is "extra" cloth in each panel, the battens are only loaded at the ends and not really loaded (therefore supported) between the ends.  And admittedly that may only apply during light to no wind conditions since as the wind increases the loads along the length of the battens increases.   

    The question then is - and esp. if the hinges allow for the battens to articulate in all planes - what keeps the hinged battens in combination with camber cut into the sailcloth from "sagging" in light conditions since there is relatively little support along their length?

    Erik

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