CE and large roach

Discussion in 'Boat Design' started by Guest, Oct 15, 2004.

  1. Guest

    Guest Guest

    when calculating the CE of the sailplan would you include the roach of the mainsail? my current project has a fairly large roach and I was wondering how others deal with this type of situation.
    I don't want to put the mast in the wrong place now do I !!

    Sam
     
  2. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Sam

    The CoE by this method is allways a ballpark figure and you may have to allow some adjustment anyway such as varying mast rake or playing with a bowsprit length. If you are working your design from a similar vessel and she has been balanced then just copy their CoE. Otherwise look for similar vessels.

    Anyway to answer your question. I always take the main as designed with full roach and the full fore triangle area.
     
  3. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Our sailboat has a Cutter rig with mast stepped 50% LWL aft of the bow.

    The roach of the 1975 fully battened main extends about 2 ft BEYOND the backstay.

    By using "pulltruded" FG battens we have never broken a batten.

    The main is great as it takes a shape from the battens at very low wind speeds giving a nice setting sail.Also great is the ability of the sail to stand and not flap it self to death when not loaded.

    Sailing out an anchor , or motorsailing in a river frequently require luffing , which the sail does with no damage.



    FAST FRED
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Typically, no, you don't count the area in the roach.
     
  5. Guest

    Guest Guest

    Thanks for the replies.
    I see we have conflicting views!!
    anyone else have an opinion? the score is 1 all!!

    Sam
     
  6. Doug Lord

    Doug Lord Guest

    voodoo?

    Definitely count the roach on a fully roached and/or square head type main. If you don't your calculations for many things will be in the mystical realm-or just plain wrong.
     
  7. Chris Krumm
    Joined: Aug 2003
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    Chris Krumm Junior Member

    I presume this is in relation to finding relationship of lead of CE over CLR, so finding the corresponding "rules of thumb" for finding corresponding underwater profile area is in order too.

    Check out the earlier "Center of Lateral Resistance " thread in the Sailboats forum. SailDesign mentioned in one reply he typically uses mainsail area with full roach with full rudder (+keel area + canoe body profile area); or no roach with 50% rudder (+keel + canoe body profile area).

    Chris Krumm
     
  8. Dutch Peter
    Joined: Aug 2004
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    Dutch Peter Senior Member

    PAR,

    Not that I doubt your expertise, but I don't understand!
    To find CE, you combine the projected areas of your sails. Excluding the roach means discounting it's effect. If the effect is so small you can discount it, leaves me with the question: why is it there?

    Regards,
     

  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I use no roach and actual head sail area for CE and 50% rudder (approx. depending on rudder design) + underwater profile (body and appendage separate) for CLP.

    Some folks use different values. Some the fore triangle area + main including roach (wise if much round) I've seen as little as 10% the rudder area and as much as 100% of the rudder area included in the CLP figures.

    People for years have been trying to increase the angle and width of the head on mains. It makes getting the most out of the height, but in machines where the last 10% of a knot must be squeezed out of the craft to be competitive, not necessarily so in more conventional designs. I was speaking of more conventional designs, which you may not have.

    If you have a big roached main, include the area in the calculations. How have you changed the rig, requiring the refiguring of your sail area?
     
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