Advice sought on mast tangs for fractional rig

Discussion in 'Sailboats' started by massandspace, Nov 14, 2017.

  1. massandspace
    Joined: Sep 2017
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    Location: Salt Chuck

    massandspace Junior Member

    I will soon be buying and rigging a mast for a small (27') sailing cat. The rig will have only 3 (three) stays...a forestay and 2 side stays. All terminate about 7/8ths up the mast.

    My question is the fittings. It seems to me that a typical "internal tang" stemball type fitting, especially for the front, will not be strong enough. I understand these are used for "normal" masts, but the last boat I owned had 8 stays total....so of course the load was spread out much (almost 3) times more.

    So, is it OK to just use the same type of tang fittings as seen on a monohull, or is there some type of "beefier" tang used in this situation?
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    You first need to calculate the forces before designing the hardware.
     
  3. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Calculating the forces is quite complicated and, without a sophisticated software I do not recommend it. It is much simpler to follow the following procedure adopted, for example, by the NBS : "In order to dimension the mast, the loading is based on the righting moment at 30 degrees of heel".
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Junior Member


    Talk to a rigger!
    Once the loads are calculated, the proper sized wire can be selected. The manufacturers of wire rope terminals match their strength to slightly exceed the strength of mating wire. Any available terminal (ball-toggle, fork, eye or turnbuckle) available for a particular wire will be appropriately sized regardless of intended end use. Wither it be monohull, multihull or architectural railing.

    But without knowing the loads involved, nothing can be decided. So talk to a rigger.
     
  5. gonzo
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    Location: Milwaukee, WI

    gonzo Senior Member

    How do you know the righting moment without calculating the forces?
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    If you know a little, just a little, of naval architecture, you can calculate the heeling moment to any list of the ship. Known this one, there are several procedures to calculate the forces that are applied to the mast. That is all.
     
  7. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Junior Member

    Part of my response did not make the upload. Continuing...

    Most masts need to be reinforced where the stays are attached. Talk to a rigger as to how this is done.

    I am most consermed about the amount of unsupported lower mast I envision from your OP. I see three scenarios.
    1. Mast so short it can't vary enough sail to drive boat.
    2. The proverbial telephone pole which will be to heavy for boat to achieve full speed.
    3. The lower portion of the mast buckling and the rig falling. Ruining the day of anyone catching it.

    Talk to a rigger as to why all those extra wires need to be.
     
  8. massandspace
    Joined: Sep 2017
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    Location: Salt Chuck

    massandspace Junior Member

    Not sure if the "contact a rigger advice " is serious or a joke.

    Of course I have already tried this. Five different riggers in fact in my local area.

    Awhile ago this type of open-minded questioning strategy worked, but now I get replies such as "Not interested", "Sure, I can help you next summer at the very earliest; seriously backlogged!", "I only do new mast consulting/fabrication and that type of rig will cost you tens of thousands of dollars", or "Why are you asking these types of questions".

    If I had the money, of course, I would not be posting on this site....would just pay and be on my watery way.

    My question again to anyone who may either own or have direct experience with an actual, in the water "relatively normal" boat with a THREE STAY ONLY fractional rig:

    "What type of tang fitting is at the upper terminus of the forestay on the front of the mast?
     
  9. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The information you provide is not enough. The mast could be 25 feet or 35 feet tall. What is the section and alloy of the mast? What is the angle of the stays? What is the beam of the boat? What is the righting moment of the boat? Etc.
    Only one forestay and two shrouds is only found in very low aspect sails with relatively thick sections. It seems like an odd choice for a multihull.
     

  10. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Junior Member

    I suspect that some of the riggers you contacted were technician rather than engineer. You were blown off because they didn't know how to properly engineer you new rig. There are people on this forum who can and will assist you, but you need to give much more details if they are to be helpful.
    Gonzo asked for more info.
    Tansl and commity already ran a bunch of numbers on your hull performance. We want to help. We love off the wall outside the box projects. Our suggestions must be based on sound engineering.

    I have owned four 3-stay boats. Each used a different attachment mechanism. In my teens I shared two Hobie cats with my three brothers. Their rigs used different attachments. At risk of being misquoted: the hardware is immaterial. Engineer first- hardware will fallow.
     
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