Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. pbmaise
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    pbmaise Senior Member

    Concur. Mother nature, g forces, and a possible faulty ANSI 54-3 conspired to cut the dyneema back stay on my aft mast rig.

    I ended up with a cut dyneema line, and shorter mast to work with. So I did.



    Here is what my new rig looks like.

    My mainsail dropped weight. It was 66 kg and is now 33 kg.

    The gaff pole helps extend the area of the mainsail. It slides up and down the same mast track as my sail.

    I like my new rig since the sails are smaller, easier to handle, and I have no concerns about reefing. I have learned to be a more conservative and slower sailor. The result is more sailing and less stress for all. Yes a passage takes longer, but used my money to buy a water maker so have no problem as long as the sun comes up to power it.
     

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  2. brian eiland
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    brian eiland Senior Member

    WOW. you really did go the conservative route. :!::D

    I think it is almost too small of a sail area myself. But I can understand about lessening the apprehensions with age ;):D
     
  3. brian eiland
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    brian eiland Senior Member

    I would have to agree there about the forces imparted to that backstay.

    Does seem as though it has stood the test of some time, ...but I have not been successful in finding out any more details on this design. Another of the Finnish participants on the forum supposedly made contact with the designer/owner and ask him to contribute, but nothing else has occurred,...it is a 'modern look' at the concept.
     
  4. pbmaise
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    pbmaise Senior Member

    Now that I have a working rig again, I am more willing to share why my aft-mast rig failed. Failure of the ANSI 54-3 occurred at a load far less than rated capacity.

    I have been employing ANSI 54-3 ceramic strain insulators for several reasons:

    They provide a separation between the Dyneema rigging and steel chain plate that is rounded and glass smooth.

    They can never rust.

    They are UV proof.

    Inexpensive.

    A pair of them with wraps eliminates the need for turnbuckles.

    Millions are employed around the world to hold up utility poles.

    ........

    The downside is they can shatter. When they shatter they are sharp and will cut Dyneema line.

    It is my belief the shattering occurred owing to them being either faulty or prestressed.

    The ANSI 54-3 that shattered was purchased in the Philippines and all other blocks purchased in Malaysia were fine.

    Therefore, besides buying good ceramic insulators, the best advice I can give is try and avoid prestressing.

    Prestressing occurs when bending large stiff wire rope around the block. You have to use multiple wire clips to hold the wire, and these also help bend the wire.

    The problem is bending the wire creates a high compression force on the block.

    Therefore, after bending the rope around the block, and moving the upper most wire clip as high as possible, unboot the upper wire clip and move it away from the block by about 1.5 cm.
     

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  5. DennisRB
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    DennisRB Senior Member

    Nice job. I think the only real way to quantify that is if you raced in a fleet of one design Nirvanas, then again after the mods to see how you compare. Just going by the feel of it could lead to the placebo effect and confirmation bias giving optimistic results. Clearly this rig does not appear often (or at all) in competitive racing of RC yachts. You could clean up if its really faster.
     
  6. DennisRB
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    DennisRB Senior Member

    Pb, Doesn't the Philippines have light wind much of the time though?

    That's an innovative use for those insulation blocks. What is the working load? Seems breaking is 20,000 lbs. Does cumulative damage occur at a lower load?
     
  7. brian eiland
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    brian eiland Senior Member

    Tony, I would submit that your mainsail should be doing a little more duty than what you have offered. It should provide constructive flow to the headsail, and could well provide additional lift of the vessel to windward via becoming a 'flap' to the rig as a whole system.

    Legitimize the Jib/Mainsail Interaction
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/sail-aerodynamics-457-22.html#post223476

    Some discussions on 'flaps'
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/sail-aerodynamics-457-39.html

    Remember this vessel did not do so well (can't find it at the moment)
     
  8. brian eiland
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    brian eiland Senior Member

    I was looking back thru some files on my older laptop and found a number of posted photos you made when you were first trying to re-rig your vessel primarily utilizing SS thimbles,...you experienced lots of problems then with these cutting into your synthetic rigging. And now you document some problems you had with ceramic insulators. Appears you were seeking some alternative 'fixtures' to the recommended marine ones.

    So it might be said that the failures you experienced with the aft-mast rig concept was more related to rigging pieces failures that the concept itself??
    There was another small trimaran that experienced such a problem as well,...the failure of a backstay fitting,...(addressed earlier in this subject thread)

    Perhaps you should have just purchased proven ones from these folks?
    http://www.colligomarine.com/

    A rig is only as strong as its weakest link.

    I am interested in some of these experiences with synthetic rigging as I have suggested the possible use of it with my aft-mast design, particularly where it might wrap around the mast tube in a 'continuous manner', rather than breaking it up into separate lines with multiple end terminations,

    ...or maybe even something like this
    [​IMG]



    BTW, it appears as though they have lots of non-stainless thimbles that work

    [​IMG]
     
  9. pbmaise
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    pbmaise Senior Member

    Well we have light winds sometimes and huge winds other. I am ready to sail now except there is a typhoon possible.

    The description is Tensile Strength:
    ANSI 54-1 is 10,000lbs,
    ANSI 54-2 is 12,000lbs,
    ANSI 54-3 is 20,000lbs.

    My Dyneema line has a lower breaking strength so that is why I concluded failure occurred far below 20,000 lbs.

    I had no canvas up. However, had short chop on beam. I could feel the sudden shifting of vessel as each small wave hit the three different hulls.

    So I concluded g forces were root cause of high load. Then load itself was likely lower than rated tensile strength.

    I reported this to the group before. The difference is now I am reporting it was possible installation error that contributed to the failure. Other than recommendations on the number and distance of wire clips to employ, I have found no recommendations of relief of prestresses like I now advocate.

    One further topic is reducing shock forces. I advocate adding a spring into the standing rigging. To do this I have pulled or plucked rigging lines with a near horizontal line with a spring in the line. This allows some give in the main back stays. I found without this spring I was constantly having to adjust the Dyneema lines owing to stretching. After the incorporation of the spring line, the Dyneema line no longer stretched.
     
  10. brian eiland
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    brian eiland Senior Member

    I don't think adding 'springs' into a rig design is a workable solution in most cases. You don't see any springs in those rigs of the big multihulls racing around the world, and often in extreme conditions.

    I think the problems you experienced was the utilization of some very 'brittle' materials in your rigging system. Ordinary glass material is very strong, but there are certainly a number of places you would not use it,..it will shatter upon impact.
     
  11. pbmaise
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    pbmaise Senior Member

    Brian,
    Certainly individual rigging components were the source of much of my problems.

    I first went with stainless thimbles which crushed like a tin can under the load.
    A machine shop in Thailand welded in a brace in stainless thimbles and these proceeded to cut the line like a knife owing to the narrow turning radius.

    "Non-Stainless thimbles appear to work" ....agreed if for a rig my size you shop at Benedicto Hardware in Cebu. They have been supplying rigging since the 1800's and have sold me some very large galvanized thimbles. These provide both the larger turning radius and cannot crush. This is what I now use on the forestay. I have to watch for corrosion since once they begin to corrode they become abrasive.

    It is clear from the photo you posted the synthetic thimbles are not on a mast 80 ft tall sitting on a platform 40 ft wide that doesn't heeel.

    Rally Tasker helped unwittingly contribute to my problems by selling me such heavy sail cloth. It was rather late in my experiments that I was adding a roller furler to my rig. Without the ability to simply roll the sail up onto the forestay, my big foresail was simply too big to manage and stow/ fold on deck. The ANSI 54-3 broke before I competed installation of a furler.

    I have concluded without a roller furler the aft-mast is not feasible for a rig.

    You may recall one key objective I had was usimg a lateen foresail.

    It did work fine during sea trial. However, two issues arose. Instead of using two spars to form a crab claw sail like shape I was only using one. That spar proved to be both heavy and bendy when made in fiberglass. It was not feasble to wrap that spar up to the forestay.

    Therefore, I believe now a loose footed Gunter style lateen sail would have been a better option.
     

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  12. pbmaise
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    pbmaise Senior Member

    Above you see my sail at Tasker and Thames barge with a loose footed Gunter and small foresail. Notice the shape of the Gunter and foresail matches the single sail I had made (I still have the larger of the two made in storage).

    What I see when I look at that Thames vessel is a great sail for an aft-mast rig.

    True there would no longer be a spirit sail, however the biggest driving force remains and is available to power a cruising sailor at an adequate speed.

    The beauty of that loose footed Gunter is no spar in the foot. To shape the sail foot requires several lines connected along the foot.

    To let out and bring in a sail of this size will require a lot of played out line for termonation points close to the clue. Very small play for lines attached near the foot.

    I have devised a method that allows a single sheet line to control multiple lines that play out varying amounts. It is only in the idea stage and involves multiple blocks so a small motion of the master control line plays out line based on number of blocks used.

    I have yet to proceed down this path and for now am content with my new smaller rig. Yes, my vessel no longer goes over 20 knots under sail, however that is for now fine by me.

    Overall, I no lomger see the biggest problem with aft-mast being backstay tension. Instead, for a big rig I see the real problem is the massive load caused by conventional jibs which are attached to one point at the clue. Sail shape on massive saiks requires massive loads at that point.

    With a loose footed lateen. load is spread out to multiple lines. Further no spar in the foot means the entire sail will wrap more easily onto the forestay.
     
  13. brian eiland
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    brian eiland Senior Member

    I must admit to not knowing the capabilities/properties of these newer synthetic rigging materials and fittings. I can only imagine there are sizes available for larger loads, as much of the world's racing fleets must be using them.

    I would imagine this is so, particularly when short-handed on a good size vessel. I know my stamina is no where close to what it use to be. And it seems like I have lost a lot of it only in the last 15 years (I'm turning 74 in a few days).

    Wonder what they make some of those fittings from,...besides alum?
    Making Your Own Deadeyes

    I just don't know enough about the details of these new rigging materials,...just they exist, and are light weight and extremely strong.
     
    Last edited: Feb 6, 2017
  14. tgtony52
    Joined: Aug 2015
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    Location: Tea Gardens, Australia

    tgtony52 ...

    Very keen on the lateen sail. In fact I have just finished building a 12' dinghy where I have used the old jib from my 24' gaff cutter ( see www.aftmastgaffcutter.com) as a lateen rig. It is the closest thing I could use that resembles an aft mast rig.

    Also while researching lateen, I came across an interesting design for a catamaran motor boat which converts it to a motor sailer. The design comes from Jeff Gilbert and info can be found in the Duckworks website (http://www.duckworksmagazine.com/07/columns/gilbert/index2.htm)
     

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  15. schakel
    Joined: Jul 2008
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    schakel environmental project Msc

    Probably already said somewhere before in this grand forum thread:
    The famed sailboat aerodynamics researcher C. A. Marchaj published this startling graph in his research paper Planform Effect of a Number of Rigs on Sail Power.
    crab_claw.gif
    Source: http://proafile.com/multihull-boats/article/proa-rig-options-crab-claw
    One can find the same rigs in the modern dhows in Arabic Emirates.
    Dhow-racing.jpg
     
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