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yard design and construction

  • 31 Aug 2012 09:56
    Quote
    Reply # 1061416 on 1061250
    Deleted user
    Graham Cox wrote:Arion now has a new yard, a 4m x 100 x 3mm alloy tube.  I have attached the halyard with a three point span spread out over the middle third of the spar, to spread the load, with a shackle between the lower halyard block and the span to increase articulation.  I have just taken it out for a short test sail and it twists off very nicely.  It remains to be seen if I bend this yard in a hard blow but I feel reasonably confident that I wont.  I have added a photo of it to my member gallery, along with some photos of Arion sailing taken by my friend, Richard Herring on his yacht, San Serif.

    Graham, I am very interested in your halyard attachment arrangement as i am about to rig the sail on Malliemac and have yet to fit a yard sling plate. Do you have a close up photograph of your new system?
  • 31 Aug 2012 04:09
    Quote
    Reply # 1061250 on 1054878
    Anonymous member
    Arion now has a new yard, a 4m x 100 x 3mm alloy tube.  I have attached the halyard with a three point span spread out over the middle third of the spar, to spread the load, with a shackle between the lower halyard block and the span to increase articulation.  I have just taken it out for a short test sail and it twists off very nicely.  It remains to be seen if I bend this yard in a hard blow but I feel reasonably confident that I wont.  I have added a photo of it to my member gallery, along with some photos of Arion sailing taken by my friend, Richard Herring on his yacht, San Serif.
  • 26 Aug 2012 22:52
    Quote
    Reply # 1057113 on 1054878
    Anonymous member (Administrator)

                                                                            Stavanger, Sunday

                       The strength of the PJR wooden yard

    I just looked up PJR Fig. 10.1 to find how the rectangular section of Hasler and Mcleod’s wooden yard is. The width is 65% of the height which, if my maths don’t fail me, means that the sideways breaking strength of that yard is 65% of its breaking strength in the vertical plane. If Hasler and McLeod had been of the opinion that the bending load was about the same on a yard in both panes, they would have designed it with a box-shaped section.

    When I made a braced yard for Johanna, in 2003, it was not just to keep it from breaking, but also to make it stiffer in the vertical plane and thus not bend and pull out the little camber there was in the top panel. I realise that I under-estimated the lateral load.

    Then, when we planned to make another braced yard with a beefed up main tube for Edmond Dantes, the upper tube was again mainly meant for keeping the yard straight. The lashed-up version was just a quick way (Plan B) to get us out sailing with the material we had since we couldn’t have it welded. After that it now has proven to work so well, I see little need to alter it. Pragmatic attitude for sure, but that suits me fine; I would go for anything that is cheap, available and good enough.

    Arne

    PS: I bet a round tube could easily be cold-milled to an oval, but it would be too expensive to have only one made.

    Last modified: 18 Mar 2013 12:12 | Anonymous member (Administrator)
  • 26 Aug 2012 21:21
    Quote
    Reply # 1057081 on 1056811
    Anonymous member
    Graham Cox wrote:Arne, a thoughtful well illustrated contribution and good lateral thinking, as always.  If my new yard shows and sign of bending I will try this.  Perhaps a similar tube lashed on the side of your yard would cure your lateral flexing in strong winds?
    ... and yet, if the yard is flexing, the best answer is a bigger single tube. A single tube is always the best way to put all the material in the place where it will do the most good. I will concede that a slight ovality in a single tube might be useful ( see the earlier topic on yards, following the bending of Annie's yard), but I can never agree that any construction involving two tubes is the best way to go, though it might be the pragmatic way to go with the materials and methods that are available at the time.

    Can anyone think of a way to "ovalise" a round tube? Cold working would increase the strength of a soft tube.
  • 26 Aug 2012 11:01
    Quote
    Reply # 1056811 on 1054878
    Anonymous member
    Arne, a thoughtful well illustrated contribution and good lateral thinking, as always.  If my new yard shows and sign of bending I will try this.  Perhaps a similar tube lashed on the side of your yard would cure your lateral flexing in strong winds?
  • 25 Aug 2012 15:23
    Quote
    Reply # 1056317 on 1054878
    Anonymous member (Administrator)

                                                               Stavanger, Sat. 25.8.2012

             Johanna's yards and Edmond Dantes' new yard

    When I fitted my 29’/3ton Johanna with a 48sqm JR in 2002, the  first yard was just an up-scaled version of the 23’/1.4ton Malena’s spruce yard, taken from the PJR, Fig 10.1. However, due to the cube factor of scaling up things, this yard turned out to bee too heavy for me. I then designed and had a workshop weld up a braced aluminium yard, cutting the weight at least with 50%. The main tube was 65mm x 3.5mm and the bracing tube was 25mm x 3.0mm. This has held up well except when a badly executed weld broke in an early, wild shake-down sail. This yard (5.8m+) is plenty strong in the vertical plane, but I can see that it is struggling a bit sideways when I press the rig at full sail. The short drift between the halyard blocks could, as Graham suggests, be a reason for this, as the yard appears to cope well with the sail reefed, even in strong winds.

    When we were to re-rig the 31’/4ton Emond Dantes with a near-copy of Johanna’s sail this year, we decided to beef up the main tube of the yard from 65mm to 80mm. This was unfortunately just before summer holidays so the workshop could not do the needed welding. We then decided to make a temporary yard by just lashing, gluing and bolting the two tubes together. See here and here. This yard has proven so good that I bet the owner will keep it as it is after having painted it to protect the epoxy (see caption under photos). On both Johanna and on ED the head of the sail is just laced to the yard. The corners (peak and throat) have been firmly lashed while along the head the load on the ties is very light. As protection against chafe, an old climbing rope has been lashed onto the yard. Not pretty, but it works.

    ED’s sail have seen quite some sailing this summer, and both the sail (48sqm / 9% camber) and its yard have held up perfectly well.

    A special asset of the lashed yard over the welded, braced version is that one can use tempered, and thus stronger, tubes. Still, ED’s yard is not of tempered alloy.

    Arne

    Last modified: 04 Jun 2017 11:29 | Anonymous member (Administrator)
  • 25 Aug 2012 14:34
    Quote
    Reply # 1056296 on 1054878
    Anonymous member
    Bruce, my yard failed 200 mm forward of the halyard attachment point.  The lower halyard block was lashed to the spar with spectra line that passed through riveted saddles either side of the yard which allowed the attachment to twist a bit.  This worked well but I really like David's idea of using a span and think I will try that this time.  The point of failure was exactly where the inner doubling sleeve ended.  I was a bit surprised to discover the sleeve did not extend further forward.  If it had extended another 500mm further forward I think the yard would not have failed, but there is no doubt that the yard was too light, being 60mm dia with a wall thickness of 1.5mm except where doubled.  I mistakenly thought I would see it flexing before it broke but it just suddenly snapped.  This yard had sailed the length of the Queensland coast on JRA member Don Halliwell's boat, supporting a flat sail of about 60% of Arion's sail area and Arion had sailed in 20 knots of wind a couple of times using the same sail with a bonnet attached bringing the sail area up to 90% of my cambered sail's area.  I am of the opinion that cambered sails do need stronger yards than flat sails.  My top panel is fairly flat but does have some camber and about 2% rounding in the head (as per David's design specs and yes, it sets very nicely even in fresh winds).  I also think the fuller lower panels may allow more vertical forces to be transmitted to the yard.

    However, I don't think there is any difficulty in building a yard that is strong enough.  It can be either carbon fibre (lightest), braced alloy like Arne and Ketil's (next lightest), or (heaviest) large sectioned, heavy walled tube, or timber.  Robert Groves uses 75 x 6mm tube and has survived some extreme weather (although his sail is not cambered).  I intend to use a 100 x 3 mm tube at this stage - if it bends I will weld a brace to it later.  The simpler, heavier yards may be harder to hoist but they come down nicely.  I made a great mistake in taking my 100 x 3mm yard off last year after damaging the throat of my sail when furling the sail.  I had forgotten to rig a fixed yard parrell and lost control of the running yard parrell when a breaking wave knocked me off my feet just as I was slacking the halyard.  The yard surged wildly and the sail could not cope with the stresses imposed.  I felt a bit intimidated by the size of this yard but realise now that a fixed yard parrell would have restrained it.  Whatever one chooses however, there is no doubt, particularly for an offshore boat, that the strength of the yard needs to be beyond doubt.
  • 25 Aug 2012 06:22
    Quote
    Reply # 1056044 on 1054878
    Anonymous member
    I recognise the phenomenon that Ketil describes - the sail I used from 2001 to 2004 had a slug slide fastened to the throat with webbing, and eventually, it showed signs of very heavy wear. That's part of the reason that I'm now using and recommending a throat hauling parrel that passes through a single block attached to the yard, so that the load from the throat hauling parrel bypasses the attachment of the sail to the yard.

    But I don't think the throat is more heavily loaded than the peak, in the direction perpendicular to the yard. If there were just a bolt rope at each end, no sailcloth, then clearly if the halyard and yard hauling parrel are in the centre of the yard, there must be equal perpendicular forces on the yard at either end, for equilibrium. Add a flat-cut top panel, and under light loads, there must be an approximately even distribution of perpendicular forces along the yard. Under higher loads, the yard must flex, the leech and luff tending to slacken, and the load must become more concentrated in the centre, limiting the load on the yard. This all results in an excruciatingly badly setting top panel. That's why I add some rounding to the head, 1 - 2%. Then  the loading changes to something between uniform loading and two equal end loads, and yes, a cambered top panel does need a stiffer, stronger yard than a flat top panel - but it's too hard to calculate exactly how much stiffer and stronger. Two equal end loads stress the yard twice as much as a uniformly distributed load, but an intermediate case is virtually incalculable.

    I think we tend to think that the peak is more heavily loaded, and fasten it more strongly, but that the throat is not so heavily loaded, and fasten it not strongly enough. 
    I think both should be equally strongly fastened to the yard.

    If a span is used, and tied to a thimble that is shackled to the halyard block, it effectively does the job of the drift between the two halyard blocks. It twists as the sail is squared off, so that the blocks themselves and the parts of the halyard between them do not have to twist. I hoist my halyard "two-blocks" under full sail, and am not seeing any adverse effects, because I have a span which is one third of the yard's length. Excessive twisting of the parts of the halyard destroys the halyard blocks and the halyard; it doesn't have any effect on the yard.

  • 24 Aug 2012 23:44
    Quote
    Reply # 1055613 on 1054878
    Deleted user
    Graham, Ketil,

    An excellent idea to gather information specific to this challenge in one place.

    I was rather caught by Ketil's impression about where the forces on the yard were concentrated as I had speculated that the forces of a cambered sail 'concentrated' more than a conventional flat sail. Are we designing our yards on an assumption that flat and cambered sail forces are identical? Is this, in fact, the case?

    (At moments like these I wish I had paid more attention in MechEng 101.)

    Graham, where along the yard did the failure occur? You mentioned the lack of a sleeve at that point I think; my speculation is that there was a concentration of force leading to a point failure. A speculation, I must add, quite intuitive and without experiential basis.

    Perhaps a gathering of specific data about failure will lead to improvement. (As an aside, is this newbie's impression that batten failure is a recurrent problem worth a new thread?)

    Bruce W
  • 24 Aug 2012 21:39
    Quote
    Reply # 1055561 on 1054878
    Anonymous member

    Hi,

    Marie G sports an old mast section braced with a 35x 3mm brace, 1000 mm in from both ends, with a plate, 5x 100x 400mm at the sling point. Sling point quite variable along the 400mm. The Mast profile is 65x50x3mm, varied up to 5mm wall thickness. I tried without a bracing stay on Edmond Dantes with 49 sqm sail, and it bent the yard downwards from the sling point, so I figured that the bracing was a necessity on Marie G s 55sqm sail. It seems to work OK, but I have not been out in a real blow yet. I was lucky to find 3 mast sections abandoned, so they didnt cost me a lot. I believe the masts belonged to the Olympic Yngling class. The masts have a groove for slides or boltrope, and the boltrope tends to be torn out of the slide at the front of the yard, so I believe that the greatests forces imposed on the rig, must be there. The sail is of Arnes design with a high peaked yard.

    Regards

    Ketil
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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