Adding spreaders

Discussion in 'Sailboats' started by swordhors, Dec 18, 2012.

  1. swordhors
    Joined: Dec 2012
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: B.C. Canada

    swordhors New Member

    Hi

    I have a 39 ft ferro ketch double ender. Because the boat is both a double ender and only has an 11 ft beam, the mizzen lower shrouds tend to lean in and cramp the ability to put on a dodger. If I put on even a short dodger over the companion way (on the starboard side) the shrouds don't give enough space for anyone to get by on that side if you have a lifejacket on.

    The current mizzen mast is only 28 ft high and has one spreader.

    I am wondering if there is any reason why I shouldn't/couldn't add a second spreader part way between the existing spreader and deck to straighten up the lower shrouds and give more room for deck-movement options when I add a dodger.
    In this scenario, there would be no lower shrouds.

    If OK, then would it be critical where the spreader went? i.e. is the a lot of calculation required to figure out where it should go?

    I've dug around on the internet a bit but haven't found any answers to this.
    I need to replace shrouds anyway so now it the time to modify.

    Thanks for your input anyone....

    Cheers

    SH
     
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Sort of like a gambrel roof. The upper spreader angle should currently have the same angle relative to the shrouds above and below but the existing spreaders tips will need to be raised to divide the new angle.
    I can't see a problem with the idea except weirdness and complication. Then you'd have to build those spreaders and reinforce the mast at the new spreader base.The height should be high enough to be out of the way. Since extra stiffening isn't necessary, height of the new spreaders could be pretty flexible.
    I guess.
     
  3. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 114, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Without a sketch or picture its difficult to understand your rig geometry and what you are proposing .
     
  4. Paul B

    Paul B Previous Member

    This was done uite often back in the 1970s on IOR racing rigs. On these single spreader rigs a second set of short spreaders were used on the lower shrouds. This allowed the lowers chainplate to be moved inboard and then the mule cold be sheeted beteen the upper and the lower.

    Your idea is a bit different (not moving the chainplate), but basically the same engineering calculations. In fact, your lower shroud would now have a greater angle to the mast (less compression).

    You just need to be sure that your mast is stiff enough in the lower panel to minimize athwartships deflection by the new spreaders.
     
  5. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    On the topic of spreaders:

    Typically, the angle of the spreader will evenly subdivide the angle made by the shroud. This puts the spreader in compression only and does not induce any torque on the spreader.

    What happens if the spreader is not normal to the shroud? Where should the spreader be if I intentionally want the spreader to lift due to the tension of the shroud?
     

  6. frenette
    Joined: May 2011
    Posts: 21
    Likes: 1, Points: 3, Legacy Rep: 13
    Location: Southern California

    frenette Junior Member

    Why don't you change that mast (aft mast right) to a free standing rig?

    I don't know if you have classic wood masts or what so can't say what to build out of.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.