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Fabricated aluminium alloy yards

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  • 04 Apr 2012 19:33
    Quote
    Reply # 881853 on 881548
    Anonymous member
    Mark Thomasson wrote:

    Especially with high-peaked yards, the yard forms a significant leading edge to the sail.  Is it worth while sleeving the sail around the yard?  (as in a Laser dinghy sail / mast)

    Stopping it rubbing is going to be more of a problem.   

    It would also allow for a larger and thinner wall section, so lighter yard.  And weight high up up is best reduced.

    One step further would be to make the whole as a wing section (Carbon on a foam core?).  As it is lowered with the sail, windage, the bane of wing mast, is avoided.  (David, how about it for Tystie's new rig?)

    Mark,
    Both Footprints' and Tystie's new sails have been made with sleeved yards. May I suggest that you look back through postings in the "New sail for Footprints" and "New sail for Tystie" topics in this forum to catch up on our progress. 
  • 04 Apr 2012 14:05
    Quote
    Reply # 881548 on 868877
    Anonymous member

    Especially with high-peaked yards, the yard forms a significant leading edge to the sail.  Is it worth while sleeving the sail around the yard?  (as in a Laser dinghy sail / mast)

    Stopping it rubbing is going to be more of a problem.   

    It would also allow for a larger and thinner wall section, so lighter yard.  And weight high up up is best reduced.

    One step further would be to make the whole as a wing section (Carbon on a foam core?).  As it is lowered with the sail, windage, the bane of wing mast, is avoided.  (David, how about it for Tystie's new rig?)

    Last modified: 04 Apr 2012 14:08 | Anonymous member
  • 04 Apr 2012 08:03
    Quote
    Reply # 881438 on 868877
    Anonymous member
    One point not mentioned:

    Annie's alloy yard didn't break. 

    Yield strength, such as metals have and timber and carbon fibres don't, is what saved our young heroine from the drama of torn sails, flailing broken spars, and the loss of pretty much all ability to raise sail. All that happened was a curve, and those are good.

    I'm not going to suggest that a ferro-cement yard, which might have cracked and failed and showered Annie with rocks and pebbles, but hung together on its metal reinforcement, would be any better. 

    Practical yards, to my mind, would include timber and alloy and composites, but not that.

    Cheers,
    Kurt
    Last modified: 04 Apr 2012 08:04 | Anonymous member
  • 02 Apr 2012 05:45
    Quote
    Reply # 874221 on 868877
    Anonymous member
    Yep, David, that's fair enough. 

    I'd add that if we could predict that the forces will be highest up-and-down and sideways, but not so high in other directions, a rectangle would be the best choice. Since we can't, I like a fat oval.

    Kurt
  • 02 Apr 2012 00:24
    Quote
    Reply # 874055 on 874007
    Anonymous member
    Kurt Jon Ulmer wrote:

    ... seems to devalue ovals wrongly, while criticising ellipses (if narrow) and rectangles (especially if narrow) quite rightly. (I hope that's clear.)

    The x-s shapes that make most sense to me are fat oval and circular. The fat oval is a concession to the routine weight-bearing direction of bend, and I think that's reasonable. Fat rectangular timber yards are easier to build, but their corners will be weaker than the smooth surface of an oval of sufficient size. Our timber yards are, needless to say, fat ovals, and I based their shape on the principles we're talking about. 

    Cheers,
    Kurt
    Kurt,
    I didn't mean to devalue fat ovals. Can we say that fat ovals and fat rectangles with a depth/width ratio of 1.5:1 or less have proved to be fully satisfactory in service, where  those with a greater depth/width ratio are suspect?
  • 01 Apr 2012 22:08
    Quote
    Reply # 874007 on 868877
    Anonymous member
    David Tyler wrote:
    ...
    I specified a round tube for Footprint's new yard. A round tube has equal stiffness and strength in all planes and is clearly not prone to instability. 
    A square tube has equal stiffness when a load is applied in line with its faces or across its diagonal - but, counter-intuitively, when a load is applied across its diagonal, it has only 71% of the strength that it has when a load is applied in line with its edges. So even here, there is a possibility of unexpected failure.
    The situation gets worse when the cross section is oval, elliptical or rectangular; but as I said above, a ratio of 1.54:1 has proved acceptable. At any greater ratio - well, I think the risk is unacceptable. 
    ...


    Hi David,

    Your discussion of cross-sectional shapes in yards suggests that all directions of bending force should be accommodated, and that it's a mistake to build as if any one direction were predominant. I agree. Fantail thinks so too.

    But the comment I've put in bold above seems to devalue ovals wrongly, while criticising ellipses (if narrow) and rectangles (especially if narrow) quite rightly. (I hope that's clear.)

    The x-s shapes that make most sense to me are fat oval and circular. The fat oval is a concession to the routine weight-bearing direction of bend, and I think that's reasonable. Fat rectangular timber yards are easier to build, but their corners will be weaker than the smooth surface of an oval of sufficient size. Our timber yards are, needless to say, fat ovals, and I based their shape on the principles we're talking about. 

    At any rate, I fail to see a single good reason for aircraft-style lightweight design in yards, especially since we can't predict in which direction nature will try to break them. 

    It's a tough life! Yards press and then bang against the mast, and get gusted around up there unpredictably, and even occasionally get pulled hard against a forgotten sail tie... 

    They need to be bomb-proof if possible, and heavy enough to come down like a stage curtain, to avoid... embarrassments.

    Cheers,
    Kurt
    Last modified: 01 Apr 2012 22:10 | Anonymous member
  • 30 Mar 2012 11:26
    Quote
    Reply # 872331 on 868877
    Deleted user
    The yards on Easy Go are made of 3 inch diameter aluminum tubing with 1/4 inch walls. They have yet to show any tendency to bend in any direction and are both light enough and yet heavy enough to bring down the sail in a blow. Each sail is approximately 30 meters. When I built these yards I felt it was overkill but I have not been let down at all.
  • 29 Mar 2012 10:11
    Quote
    Reply # 871516 on 871192
    Anonymous member (Administrator)
    David wrote:   If such a short yard is used on a HM rig, the whole thing would need to be the subject of experimentation, to see what the side effects were.


    I see the point. I had this possibility in mind when I fitted a new type of lazyjacks to Johanna last summer. Still it should not be difficult to fit a fairly lightweight yard extension in case it turns into a real problem. I notice that it looks as if Annie has kept her two top battens at full length and just let them stick out this way. That makes sense.

    Arne

    Last modified: 29 Mar 2012 10:20 | Anonymous member (Administrator)
  • 29 Mar 2012 01:49
    Quote
    Reply # 871192 on 870482
    Anonymous member
    Arne Kverneland wrote:The use of a shorter yard than the lower battens, as on Fantail’s sail seems to make a lot of sense. I used the same method when designing the rig for the schooner Samson, with HM-style sails. The idea with doing it was to reduce the size of the top panels to keep control of the twist, but a good side-effect was to save weight of the (wooden) yards. On Samson’s main sail the lower battens are 6.7m, the top batten 6.4m and the yard 6.2m. I guess I will make use of this method more often on big sails.

    Arne

    Just one word of warning: the shortest yard that I could achieve for the Fantail geometry of sail is 75% of the batten length. Any less, and there is a risk of getting inside the topping lifts at the aft end, and coming clear of the mast at the forward end.
    This length appears to be OK on the Fantail sail, because of the particular way the battens and yard position themselves as they are furled, provided that:
    • the mast is raked forward, or
    • the sail can move forward as it is lowered, or
    • the yard has a fixed parrel, like a batten parrel, to avoid the risk of it coming clear of the mast
    If such a short yard is used on a HM rig, the whole thing would need to be the subject of experimentation, to see what the side effects were.
  • 28 Mar 2012 18:13
    Quote
    Reply # 870766 on 870482
    Anonymous member
    Arne Kverneland wrote:

    PS, a couple of hours later: I just found a Q-CAD drawing of Fantail’s sail which let me find the length of battens and yard. The yard, at only 3.75m, should come out pretty light, less than ¼ of Johanna’s wooden yard and just over half of the 4.6m yard on Malena’s sail. This kind of shortened yard may call for slightly stronger top battens due to raised compression*, but overall one should still save quite some weight with a yard that is made so much shorter than the boom (4.85m). The more I look at it, the more I like it.

    *This appears to be the case. On Footprints, the cedar/glass battens that were just adequate on a flat HM sail are bending way too much in the top of the sail. David Thatcher has got three lengths of 65 x 1.6 tube to make new top battens.
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