Wings for Bi-Plane Catamaran

Discussion in 'Boat Design' started by Cat2Fold, May 20, 2014.

  1. Cat2Fold
    Joined: May 2012
    Posts: 56
    Likes: 1, Points: 0, Legacy Rep: 13
    Location: Felt, Idaho

    Cat2Fold Junior Member

    Hi everyone,
    So, my beloved Cat2Fold needs new sails this year.
    I'm trying to decide what to do...
    Buy expensive new sails ($$$)? (I got a quote from North for $16,500 for two new 3di mains)... Ain't happening unless I win a lottery or something.
    Buy cheap new sails that I'll be unhappy with in relatively short time...($$)?
    Or...if I were to try and build my own...
    Build reefable, two sided, double element soft wing sails ($)? (Possibly cheap, flat fabric construction (Tyvek?), I'd still need a sewing machine (or maybe just Tyvek tape?) and the time to learn to use it, battens built from ply/glass at hinges, and small carbon rods...???
    Something like this blue DIY blue tarp soft wing... (See image below)
    Or, when I think about my skills and tools I already have, building some high aspect, fixed wings with tail flap controls is VERY appealing!
    No sewing machine or sewing skills needed.
    Should last longer.
    Easier to use.
    Probably ALOT harder to step/unstep (crane needed?)...
    I already have freestanding carbon masts that weigh in at 100 lbs....
    So, I'm looking for some feedback on which way to go.
    I'm leaning toward 8' chorded, rigid, single element wingsail with tail control and counterweight.
    Single element, and 8' chord throughout the 31' height, is for easy build and K.I.S.S...
    8' chord allows legal trailering width...
    See here...
    http://www.ivorbittle.co.uk/Article... sailer/The wing-sailed yacht for the web.htm

    I could build the tail control and the counter weight so they are relatively easy to remove for those once-in-a-blue-moon times that C2F needs to be parked in a Marina.

    My current sails are about 14'9" in the foot. 31' luff...
    Any thoughts?
    Would two (single element) wings at ~250 square feet perform as well, better, or worse than my current Marconi rig of nearly 300 square feet? I imagine downwind would need some spinnaker help, but pointing and reaching?
    I hope this post is understandable and in the right place.
    Thanks for any and all advice!

    ...and yes, I do understand fixed wings can't be reefed.
    I am a bit crazy, and tend to do things differently than most!:D
    ...oh yeah, and I'm broke, but I've got mad tinkering and building skills!
     

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  2. Skyak
    Joined: Jul 2012
    Posts: 1,194
    Likes: 25, Points: 38, Legacy Rep: 152
    Location: United States

    Skyak Senior Member

    3di or tyvec? I think you need to consider materials that are not not top end or below the bottom end. On a boat the size of yours, nothing worth doing is worth doing in tyvec.

    Hard wings? Really? You are not thinking about the continuous care and handling. Hard wings are the perfect way to make your boat sit and gather dust.

    Your boat has fairly easily driven hulls so higher performance sails pay. Your boat doesn't heel so don't pay too much for light weight. I like the idea of soft wing sails because the shape is in the battens -you don't need to be an expert to cut and sew them. Lots of battens will keep stresses low in the fabric so they will last longer than conventional sails in the same fabric. The double sided forward end could be lighter woven polyester for easy furling since it is low stress. And the single sided leach can be stiffer material. It can be very flat without performance penalty.
     
  3. Cat2Fold
    Joined: May 2012
    Posts: 56
    Likes: 1, Points: 0, Legacy Rep: 13
    Location: Felt, Idaho

    Cat2Fold Junior Member

    Thanks for the response Skyak...
    Yup, I'm all over the place with my thoughts.
    If I were to try and build a double element soft sail, I still have some questions...
    What foil shape would be best for the leading element on my boat?
    How about the aft element? Single skin only? Another double skinned foil?
    Hinged battens?
    What percent chord should the elements be? 50/50? 60/40? 70/30???
    How big should I make it? I have right around 17' between the masts (center to center).
    With my current sail being a low aspect 14'9" foot, 31' luff sail, should I try and match the sail area?
    How much of element one should protrude out forward of the mast?
    Should I build the sail as a simple rectangle with the head and the foot both the same length? Or, should I taper the sail from bottom to top.
    Obviously, a rectangle using the same size battens all the way up would be easier to build, but that isn't the only priority.
    I imagine higher aspect ratio would be nice, but I don't want to lose sail area.
    I'd prefer speeding the boat up rather than slowing her down.
    I appreciate your comments about not using Tyvek on my beautiful boat...I'm just budget challenged at the moment...
    Is Sunbrella an example of a light woven polyester that you mention?
    Thanks for your responses, I REALLY appreciate it!!!
     
  4. tevake118
    Joined: Jan 2013
    Posts: 19
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: Goodland, Fl.

    tevake118 Junior Member

    hi: have you read the thread on this site "design of soft-wing sails for cruising"? Also, Bernard Fercot's Grand PHA is currently on the way to Tahiti after he has extensively documented the development of his bimast wishbone junk sail catamaran on"Wharram Builder's Forum". You are aware of this, right?
     

  5. Skyak
    Joined: Jul 2012
    Posts: 1,194
    Likes: 25, Points: 38, Legacy Rep: 152
    Location: United States

    Skyak Senior Member

    You have been on "design of soft-wing sails for cruising" forum. I find all of his choices fine in theory and beyond my knowledge base in practical use. Use his design for guidance, particularly his batten design. As far as proportion of the two elements 50/50 would be fine. I would consider as little as 30/70 based on the 2D analysis I have seen. I am considering making a similar soft wing for my laser for fun. The reason I don't favor a larger forward element is that it is harder to reef and set -the big downside to soft wing. As far as size goes I see no reason to go smaller because upper size is limited by drag which is smaller on the soft wing. I would have a constant length at the bottom and taper toward the top with an elipse shape as my guide. I think Sunbrella is an woven acrylic. Polyester is cheaper and available in low stretch.

    As far as profiles go I think a fairly tame NACA profile forward is all that is needed. The only thing I would watch for is to be sure that laminar flow does not reach past the front element to the second one. That could make a sail with finicky laminar separation. The one difference I would expect between your profile and the one on the cruising mono is that yours would not be as thick. Your masts are skinnier and your boat is faster so I would expect less camber.
     
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