Bow Sprit Length & Rise above horizontal?

Discussion in 'Multihulls' started by Seann N Me, Dec 16, 2010.

  1. Seann N Me
    Joined: Dec 2007
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    Location: New Port Richey, FL

    Seann N Me New Member

    I have just had a 6' bow sprit added to my 45' Voyage Catamaran. My question is how much above horizontal should the sprit be if any at all. The sail maker has installed it with to much rise in my opinion (better than 1.5ft above horizontal), due to the fact when it gets loaded up it pushes downward on the cross bar. I have 1000sqft sail, Mylar scrim Base Material - Dimension PM 10 Taffeta Polyester w/ Aramid Tapes and light weight Sun Cover, useing with Harken CO-2 furler. Sail designed for light wind, I try to keep it at 15 knts apparent wind. At 15knts apparent I am getting downward deflection. I believe if I lower the tip of the pole my deflection will be less? Any help or ideas?

    E. J.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    It depends on the shape and rigging of the cross bar. If you are adding a load, a strut and stays should be adde to counteract the force. If it pushes back the deflection will be the same but in a different direction. The reason for a raised bowsprit is to prevent it from getting under water when the seas are big.
     
  3. Seann N Me
    Joined: Dec 2007
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    Location: New Port Richey, FL

    Seann N Me New Member

    There are stays running to the inside of the hulls at water line, voyage has double struts running from the cross beam to the bridge deck suporting a teak walk way between tramps. I understand the concept of raising the sprit to limit going in the water. But as you raise the tip the load shifts more in a downward fource on the beam as well as inward. Dipping in the water is not a huge issue of concern, looking for some insite on horizontal..If dipping in the water is not a major issue, would dipping down the tip of the sprit slightly fource the load up and in? Which is the natural fource of the headstay on a catamaran? That is the purpose of the A frame support on the cross beam. All input is welcome.
     

  4. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member

    Pin jointed vectors

    If - and I suspect it is - your prodder is mounted on a hinge then it is easy to work out the vectors from the prodder pole - they are in line with the prodder. (There could be some moment if the pole was hard mounted)

    So get the pole exactly horizontal and it will not put any upward or downward vector on your fore beam. The amount of compression on your catwalk stuts (or whatever you have to stop the forebeam pulling aft in the middle) will rise slightly but it will be insignificant.

    In Aus almost all prodders are horizontal. Unless your boat is low freeboard it should be fine to go flat. Although I am surprised you can see deflection. Code 0s do pull a huge luff load - thinking about it my forestay does go a bit slack when I am close reaching in 15 knots. I have seen a couple explode at the prodder to forebeam connection - be careful here.

    cheers

    Phil
     
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