advice sought on sailing rig for mini-cruising catamaran

Discussion in 'Multihulls' started by massandspace, Nov 11, 2017.

  1. massandspace
    Joined: Sep 2017
    Posts: 17
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    Location: Salt Chuck

    massandspace Junior Member

    Hello:

    I am looking for advice on a sailing rig I am designing for a custom catamaran. The boat is a 27' long by 14.5' wide cruising cat....not high performance....but would like to see speeds around 9-10 knots if possible. It is a foam/epoxy build....so pretty light and stiff, although it was not vacuum bagged and the like so not super light either. I think the final weight of the boat will be about 4,500 lbs.

    I have attached a screenshot of the front end of the boat from the Rhino file that I have drawn. Also willing to share that 3D file if anyone has a computer program that can read it (.3dm and I can save it as others as well).

    My main question is would it be OK to build the bowsprit and have that be the terminus for the jib...so it would have to be for UPWIND work as well...only one jib is way I want....I have heard/read that sprited sails only really work for cross or downwind, but in my opinion if the sprit is built strong enough why can't it be used for upwind as well?

    The boat will be a full pilothouse mini cruiser, so the pilothouse makes it hard to design a sailplan with a large enough jib. The sprit seems to solve that by giving me more area, and also will lower the center of area of the sails....and this is important as my beam is only slightly more than 50% of my length and I want to keep the center of the sailing plan as low as possible...not sure if that is the right term.

    Thanks for you attempt to help.

    David
     

    Attached Files:

    Last edited: Nov 11, 2017
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    That, probably, is not the correct term because, in general, the righting moment (righting arm) is intended to be as large as possible.
     
  3. hump101
    Joined: Oct 2004
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    Location: Brittany, France

    hump101 Senior Member

    Putting the jib on a sprit is not a problem as long as the sprit is strong enough to maintain enough luff tension AND the resulting centre of effort (CoE) of the rig matches the centre of lateral resistance (CLR) of the hull and appendages. If the hull is already built, then this CLR position may not be easily adjusted, and hence the CoE needs to match it.
     
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Some say that, for mono hulls, between the CoE and the CLR there must be a lag that can be between 10% -12% of the boat's length. Maybe for catamarans it's different.
     

  5. guzzis3
    Joined: Nov 2009
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    Location: Brisbane

    guzzis3 Senior Member

    Yes, it's much lower. Obviously for each boat it is different but it's close to 0, maybe 5% at most. The reason is cats only heel 5 degrees normally before bits start getting airborn. Monos are often sailing at signifigant heel.

    Sprited jibs have been done, as said if it's strong enough that won't be the problem. Lee helm will be the problem. You may have to lengthen your main sail aft.

    Have you considered instead just living with smaller jib and having a bigger main ? I assume you are going to have about 31 sq meters of sail on that boat and about a 10 meter mast ? stepped about 3.5 meters from the bow ?
     
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