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  • 29 Sep 2017 11:51
    Quote
    Reply # 5287243 on 5283141
    Anonymous member
    Kurt Jon Ulmer wrote:
    Quite right. You'd hardly need battens at all, once rid of that pesky yard...

    But Richard! You've practically reinvented the Bermudan rig, right here at the JRA! Your courage does you credit... nobody's ever dared that before!

    Don't worry they are busy coming the other way. What do they call the spar at the top I wonder.
  • 28 Sep 2017 07:10
    Quote
    Reply # 5283532 on 5280481
    Anonymous member
    Arne Kverneland wrote:
    Richard Brooksby wrote:

    ...

    Most of the replies here are (I think) discussing horizontal failures. I am curious to analyze the forces.

    ...

    My braced yard on Johanna bent  vertically at the sling point when a weld between the brace and the main tube broke. Later, it held without taking any permanent bend to any sides. I like to think that this is because the side-forces are lighter than the vertical forces, since there was no bracing sideways on that yard.

    ...

    Arne


    My best guess is that the weakness (brittleness) of welded aluminium was at fault. The same amount of slight deflection that caused that break, in my guess, had probably been happening in other planes too - it's just that there was nothing to break, and the yard could spring back.

    The damaging force was less than the yield (permanent bend) threshold of unwelded tube, but just greater than what was needed to break a weld, one which may already have suffered fatigue from the small deflections all around it.

    A welded brace (or any local weld) creates a discontinuity which concentrates strains at... the weld.

    Bend, yield, break - the tendency of a weld is to stand firm, or break.

    Kurt
  • 27 Sep 2017 21:38
    Quote
    Reply # 5283141 on 5281897
    Anonymous member
    Richard Brooksby wrote:
    Kurt Jon Ulmer wrote:Some people are using shorter yards these days. That might be a good idea, if the next batten down can handle it...
    You are anticipating me again, Kurt. My next thought experiment to write about was this: imagine a sail where the battens get shorter towards the top. Then imagine one where the yard has zero length. Presumably the forces are distributed among the battens.

    Quite right. You'd hardly need battens at all, once rid of that pesky yard...

    But Richard! You've practically reinvented the Bermudan rig, right here at the JRA! Your courage does you credit... nobody's ever dared that before!

    (Well, I suppose Paul McKay...  on his way laterally to the AeroJunk. Thanks, Paul!)

    Cheers, Kurt
  • 27 Sep 2017 09:37
    Quote
    Reply # 5281935 on 5280481
    Anonymous member
    Arne Kverneland wrote:
    Richard Brooksby wrote:

    I think I have been somewhat mislead by looking at the bridge-like yards on Amiina, Emmelène, an Johanna into imagining that the main strain on the yard is vertical. My own wooden yard (straight out of PJR) is only tapered in the vertical direction. Most of the replies here are (I think) discussing horizontal failures. I am curious to analyze the forces.

    Actually, I think PJR got their wooden yard quite right. The width-to-height ratio at the sling point is 65%, and it is 70% at the ends. Their yard surely is tapered in both directions.

    You are right! See PJR figure 10.1 and chapter 10 which says “…the dimensions of a solid spruce yard whose underside is straight and whose depth and thickness are tapered from the sling plate towards either end.”  I don't think mine is, so that's a deviation. I'll double check this when I'm next aboard.

    This means that the yard is 65-70% as strong sideways as in the vertical plane. Btw, since the load on the yard is highest in both directions at, or near (at the mast) the sligpoint, so there would be no help in not tapering the yard.

    Exactly.
  • 27 Sep 2017 09:31
    Quote
    Reply # 5281933 on 5280864
    Deleted user
    Kurt Jon Ulmer wrote:

    Some people are using shorter yards these days. That might be a good idea, if the next batten down can handle it...

    Cheers, Kurt

    The yard on Footprint's sail is quite short, only 5m length for 53 square metre sail. It was almost 7 metres long for the previous HM pattern sail of the same area so I cut a meter off each end of the yard when refurbishing it for use with the new sail. The top batten is carbon tube so is very strong and I have never seen any bend in it, but the original top batten was alloy tube which did develop a bend. The yard on Footprints is quite vertical, and the sail is essentially square topped with the top of the top batten as high as the top of the yard, so all the bending load is from the vertical pull on the top of the yard. That is the bend I see in the yard, and it occurs when Footprints is hard on the wind in a stiff wind. I have never seen any bend in the yard when sailing off the wind.
    Last modified: 27 Sep 2017 19:26 | Deleted user
  • 27 Sep 2017 09:18
    Quote
    Reply # 5281897 on 5280864
    Anonymous member
    Kurt Jon Ulmer wrote:Some people are using shorter yards these days. That might be a good idea, if the next batten down can handle it...
    You are anticipating me again, Kurt. My next thought experiment to write about was this: imagine a sail where the battens get shorter towards the top. Then imagine one where the yard has zero length. Presumably the forces are distributed among the battens.

    Maybe I can build some strain gauges into my next sail's battens.
  • 26 Sep 2017 20:23
    Quote
    Reply # 5280864 on 5276531
    Anonymous member

    mehitabel's yards are fat oval in section, barrel-tapered to the ends, because I couldn't pick any one direction to weaken more than any other. It was clear that there would be a fulcrum near the mast (or parrels, on the starboard tack) and that the sail, attached downward (by sheets, tackline, downhauls, bundle weight) would transmit sailing strains upward to the yard. Thus oval, not circular.

    To properly analyse what can happen to a yard will always be beyond me. If I ever break one, I hope I can figure out roughly why...

    Some people are using shorter yards these days. That might be a good idea, if the next batten down can handle it...

    Cheers, Kurt
  • 26 Sep 2017 18:55
    Quote
    Reply # 5280481 on 5280148
    Anonymous member (Administrator)
    Richard Brooksby wrote:

    I think I have been somewhat mislead by looking at the bridge-like yards on Amiina, Emmelène, an Johanna into imagining that the main strain on the yard is vertical. My own wooden yard (straight out of PJR) is only tapered in the vertical direction. Most of the replies here are (I think) discussing horizontal failures. I am curious to analyze the forces.


    Actually, I think PJR got their wooden yard quite right. The width-to-height ratio at the sling point is 65%, and it is 70% at the ends. Their yard surely is tapered in both directions. 

    This means that the yard is 65-70% as strong sideways as in the vertical plane. Btw, since the load on the yard is highest in both directions at, or near (at the mast) the sligpoint, there would be no help in not tapering the yard.

    My braced yard on Johanna bent  vertically at the sling point when a weld between the brace and the main tube broke. Later, it held without taking any permanent bend to any sides. I like to think that this is because the side-forces are lighter than the vertical forces, since there was no bracing sideways on that yard.

    The yard that Ketil describes, is of the same dimension as Johanna's yard. As said below, we went up a number in size when we made a new yard for Edmond Dantes.

    Arne
    Last modified: 27 Sep 2017 11:21 | Anonymous member (Administrator)
  • 26 Sep 2017 17:35
    Quote
    Reply # 5280336 on 5276531
    Anonymous member

    Most yardbending happens when running With 34+ knots of Wind, full sailarea and surfing 10+ knots. It is also mindbending and quite wet, but I love the speed and thrill. The latset yard is 65mmx 3.5 wall, 6 meters long, and it bent where the Welding for the slingpoint and brazebar is. Welding aluminum weakens it, so I will try With soft slingpoints NeXT year. My sailing is inshore, and the engine Works, so I am not too conserned about it.

    Ketil
  • 26 Sep 2017 16:10
    Quote
    Reply # 5280148 on 5276531
    Anonymous member

    I think I have been somewhat mislead by looking at the bridge-like yards on Amiina, Emmelène, an Johanna into imagining that the main strain on the yard is vertical. My own wooden yard (straight out of PJR) is only tapered in the vertical direction. Most of the replies here are (I think) discussing horizontal failures. I am curious to analyze the forces.

    If the yard were vertical then it would be like a topmast or gunter, and so have forces acting on it like a mast. Lifting forces would be compression forces.

    If it were horizontal, it would have forces acting on it like a square rig yard. Lifting forces would be cantilever bending forces.

    On a run (with the sail acting as drag), both orientations would experience cantilever bending forces.  A vertical yard will experience extra compression forces due to tension in the sail, and a horizontal yard extra downward bending forces.

    Upwind (with the sail acting as a wing), I can't easily visualize the forces caused by the lift.

    Does any of this sound remotely right?

    Why do we not taper our wooden yards horizontally as well (like a double truncated cone)?
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