Dux Diamonds

Discussion in 'Multihulls' started by catsketcher, Aug 4, 2015.

  1. HydroNick
    Joined: Apr 2010
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    Location: British Columbia

    HydroNick Nick S

    Phil:

    Photo showing shrouds is attached, it is the best shot I have..I should take some photos of some of the soft rigging bits. The shroud has a Colligo Distributor (black) on the bottom of its main section (I believe it was a Colligo Terminator 7-9 mm Open, Black; CSS71-O) and then two Precourt (now out of business) fittings at the bottom for adjusting/ lashing to the chainplate. Colligo has, I believe similar fittings. The lower ~metre of the shroud is doubled and this was a function of me doing the final splice of the Precourt fitting to the shroud myself. The shroud tensioner is attached to the lanyard also from the distributor (John Franta indicated the Distributor was OK for this 3-way pull) and the tensioner is shown cranked up with a significant dog leg in the shroud which is warned against by Farrier when under load...so the tensioners get slacked off when sailing so that the shroud is essentially straight. The large difference in shroud tensioner tension between sailing and resting is a result of my inability to fold the boat properly if the shrouds have been adjusted close to straight (i.e. the tensioner in that case is almost redundant) when the floats are extended (any advice or comment on this would be appreciated). The top of the shroud is a thimble that attaches to the jesus shackle (I love that name). As noted by someone else on BoatDesign.net. ...possibly in the soft rigging thread,...the thimbles have to be thimbles designed for synthetic line as the thimbles for wire will compromise the strength of the Dyneema. I am not sure that I would trust Antal rings for this, certainly not against the ss shackle...though I do love Antal rings.

    The forestay (no photos I am afraid) has thimbles at each end and uses a Colligo Chainplate Distributor for Sprint-Forestay, 3/8", Black; CSS94.5 lashed to the lower thimble.

    If any one is interested, in my basement I have many pounds of almost new ss F-25c rigging, courtesy the previous owner!

    Regards

    Nick
     

    Attached Files:

    Last edited: Aug 10, 2015
  2. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    I'm trying to understand why you need 'adjustment" in the forward portion of the shroud termination at the ama hull?

    I also wonder about why Farrier warned of a problem with a dog leg in the shroud??

    I utilized a split shroud on the Firefly trimaran to take the loads directly to the aka beams rather then the ama hulls, and to provide an side-to-side stabilizing force to the mast when hoisting it during a trailer launching. I had only one block/tackle arrangement on the aft strand of the split shroud to tension everything up.
    Firefly 26.jpg
    Dick Newick had utilized a similar arrangement on one of his small tris.
     
  3. HydroNick
    Joined: Apr 2010
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    Location: British Columbia

    HydroNick Nick S

    Brian: From the Farrier sailing manual

    When initially setting up, stays with [shroud] tensioners must be adjusted to be just long enough to reach chainplate. There will then only be a small deflection when the tensioners are applied. Avoid the shrouds being too long as the resulting large deflection will put too much load on the tensioners, and this could put the mast at risk

    I will admit this doesn't completely answer your question...but there it is. I thought I also read that if the shrouds are too deflected the force on the chainplate is in the wrong direction but I am afraid I could not readily find that quote

    Regards

    Nick
     
  4. paxfish
    Joined: Dec 2014
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    paxfish Junior Member

    Groper - What type of whipping do you have on there? Just regular polyester?

    I need to do something like that because I often use my shrouds a handhold, and they are showing a bit of wear....
     
  5. brian eiland
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    brian eiland Senior Member

    Perhaps his concern was about the block and tackle being utilized to provide the tension,...as to whether it was up to spec of taking the load. Or perhaps the jamming mechanism of that block/tackle?

    I know I was very concerned that the jamming cleat was PROPERLY engaged, and protected from accidental disengagement,...resulting in the mast going overboard due to lose of all shroud tension. I was NOT concerned with the larger 'deflection from straight' angles of the split rigging.
     
  6. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    Mine do not use whipping or twine as chafe protection but a pre manufactured braided sleeve which slips over the shroud. Same stuff is also used over the seagull striker where the dux contacts the aluminium etc. I don't have good photos which show it, but you can see it in the previous video I posted earlier in this thread. The braided sleeve is black in colour...
     
  7. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    With the tensioners you really only want a small deflection of the load in BOTH of the lower parts of the load gets greater really quickly.

    If you draw right angle triangles with the vertical part being the full load of the sidestay being taken by the vertical part (above the tensioner) then if you make the triangle small on the base then the hypotenuse will be very similar in length (and therefore load) to the vertical part. So the "bent" part of the stay, tensioner and lower stay. are pretty similar in tension to the rest of the stay. The load the tensioner has to apply sideways, being shown by the length of the base is also very low.

    Broaden the base of the triangle and things get bigger. A 45 degree angle increases the loads by 1.4, getting down to 30 degrees and the loads get to double. The loads on the tensioner are now larger than that on the rest of the stay above the bend. These angles are why a seagull striker wire is always so stout.

    To get around this it may be possible to change your chainplate position to the inside of the float so that it reduces the length of the stay as the float is folded.

    In Brian's case it is trivial to make a bridle like in a seagull striker but few would want one part of the bridle to be an adjustable block and tackle so I can understand Farrier's request for deflection to be kept low.

    cheers

    Phil
     
  8. brian eiland
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    brian eiland Senior Member

    Several of Newick's
     

    Attached Files:

  9. HydroNick
    Joined: Apr 2010
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    Location: British Columbia

    HydroNick Nick S

    Thanks Phil: I did eventually find the tips document...on my computer at work. No idea how it would have got there.

    The additional comment from Farrier was that if you put high tension on the tensioners (which only cleats) then if the cleat lets go under high load chances of losing the mast are good.

    Nick
     
  10. brian eiland
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    brian eiland Senior Member

    ..slightly modified wording from previous posting, but expressing same reasoning...

     

  11. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    By T-balls I assume you are talking items like this?
    T-ball Termination1.jpg

    T-ball Termination2.jpg
    I know these are widely used in the rigging world, but I was never a fan of them. I just don't care for the loading on such an off-center, 'cocked' fitting.
     
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