Mast heights, boom lengths and aspect ratios

Discussion in 'Sailboats' started by Allan Jennings, Nov 21, 2005.

  1. Allan Jennings
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    Allan Jennings Junior Member

    I am building my boat 53 foot Roberts, the design the end of the boom ends up over the steering wheel. If I lengthen the boom there will be bending moment introduced into the boom and spare length not used. What happens if I increase the length of the foot and shorten the mast to maintian sail area,- do I lose performance? It is not a racing boat so would it really matter? At the moment the aspect ratio of the mainsail is 3:1. With an extended boom it comes down to 2.5:1. Either that or any ideas on the main sheet as i do not want it in the cock pit?
     
  2. D'ARTOIS
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    D'ARTOIS Senior Member

    Why do you want to lengthen the boom? What is the issue?
     
  3. Allan Jennings
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    Allan Jennings Junior Member

    I need to connect the mainsheet to the boom. The traveller has to go either behind the cock pit in which case the boom isn't long enough or on the coach roof where it is going to be too close to the mast.
     
  4. panthablue
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    panthablue Junior Member

    Boom length

    I had the same dilemma when I built my boat. In the end I opted to have a long boom with the mainsheet traveller at the stern of the cockpit. it works perfectly.

    Dissadvanteges - weight of increased length of boom
    Advantages
    mainsheet traveller is out of the way
    Mainsheet can be adjusted by the helmaman just like dinghy sailing
    the mainsheet fittings can be lighter because the load is less due to the longer boom length. (force x distance)

    Good luck with it
     
  5. TimClark
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    TimClark Senior Member

    You should be able to put a traveler bar right infront of the wheel that is seat height. That's how it's like on most of the J Boats. Good Luck.

    Tim
     
  6. Vega
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    Vega Senior Member

  7. panthablue
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    panthablue Junior Member

  8. FAST FRED
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    FAST FRED Senior Member

    From an aerodynamic point you don't figgure aspect ratio by simply dividing boom legnth into sail hoist.

    Span (hoist)squared divided by area , with an optimum for a cruiser at 6-1 seems to work well.

    The formula works for jibs too.

    FAST FRED
     
  9. MikeJohns
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    MikeJohns Senior Member

    What about a combination boom gallows and main sheet track above the cockpit ? With a longer boom you might need a tripping reef in the main to keep the boom end away from the waves in boisterous seas.
     
  10. Allan Jennings
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    Allan Jennings Junior Member

    What's a tripping reef?
     
  11. MikeJohns
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    MikeJohns Senior Member

    A tripping reef is a reef line that extends from the tack to a point several feet above the clew on the leech. Its purpose is to raise the boom end.
     
  12. HeloDriver
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    HeloDriver Junior Member

    ' tripping reef

    More commonly called a 'flattening reef'?

    ____________
    HD
     
  13. julleras
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    julleras Junior Member

    Allan:
    I would check that by lengthening the boom (and the mainsail, I suppose) you do not diminish too much the lead of the Center of Effort vs the Center of Lateral Plane. You could end up with a LOT of weatherhelm.

    Check with the designer.
    There's a good discussion in http://boatdesign.net/forums/showthread.php?t=1898&page=
     
  14. Allan Jennings
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    Allan Jennings Junior Member

    OK So I will keep the original sail plan and just make the boom a little bit longer so the mainsheet drops behind the cock pit seat and fit a tripping reef so that the boom is lifted when heeling in strong winds to stop the boom from dipping in the sea.

    The only thing to work out is how much longer do I have to make the boom, does the mainsheet need to drop vertically from the end of the boom when the boom lies on the centre line of the boat or can it be inclined parallel to the topping lift?
     

  15. sharpii2
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    sharpii2 Senior Member

    The more perpendiculer (vertical) it is the more effective it will be. 10 to 20deg off is not too bad though (98 to 94% effectiveness, respectively).

    Bob
     
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