Ketch standing rigging resources

Discussion in 'Boat Design' started by CanuckGuy, May 6, 2016.

  1. CanuckGuy
    Joined: Aug 2008
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    CanuckGuy Junior Member

    Hello all,

    I'm working on a self-design, self build ketch. I have used ISO 12215 and Principles of Yacht design to guide most of the scantling work on the boat, and at times consulted with a naval engineer regarding big pieces (e.g. keel, rudder).

    I've worked out the entire dimensioning for my main mast, however, I'm having difficulty finding good literature on mizzen standing rigging for ketches.

    I have read (and up until now agree with) that triatic stays reduce redundancy and end up taking down the mizzen when the main goes, so I would like to avoid a triatic stay. But then all sketches and schematics I see are that the entire fore-aft staying of the mizzen occurs from lower aft/lower fores, and swept back outer stays.

    Is this really the only common layout? (I actually can't really think of a functional alternative) If so, how do I adapt standard stay calculations (e.g. the ones in PYD) to accommodate for a swept back rig that has no fore/aft staying?

    Details are that the ketch is 42', 9t disp, mizzen mast is deck stepped single spreader. Sail area is 12m^2.

    Thanks for your time.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You're over thinking this. If your boat is in a situation, where the main is knocked down, having the mizzen dragged down with it will be one of the lesser concerns initially. Once you've gathered you wits, the boat has righted, you've checked for leaks, hull damage, cut away the rig so it can't hole the boat, clear the pump inlets from the inescapable clogging they get with the knock down, etc., then you can worry about the choice of mizzen rigging being tied to the main. I don't like the triatic for similar reasons, so I like spit backs on the main with significant rake on the mizzen lowers and cap. If able to fly a good size mule, then runners might be needed, but usually not.
     
  3. FAST FRED
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    FAST FRED Senior Member

    When staying the mizzen be sure the rigging is robust enough to handle a mizzen staysail.

    These are great light weather rigs to help move a ketch.

    The sail will be about the area of the mainsail, perhaps larger , so the mizzen rigging must be substantial.
     

  4. CanuckGuy
    Joined: Aug 2008
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    Location: North America

    CanuckGuy Junior Member

    Thanks for the replies.

    So essentially I should do the dimensioning as though the mizzen was a backstay-less main mast (appropriately sized). The swept backs should factor in enough strength to counter the forestay load of a loaded stay sail.

    And what about the lower forwards? I just assume the load of a backstay (i.e. through PYD method) and use trig to figure out the load as it applies to them?
     
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