Designing about 4.5m long trimaran

Discussion in 'Multihulls' started by TTTP, Feb 17, 2008.

  1. TTTP
    Joined: Feb 2008
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    TTTP Junior Member

    Impressive building speed. Are you going to paint it?
    Sounds good. Because of size and design compromises my boat would never sail extremely fast anyway.
    I have thought about spruce core with fiberglass skins.

    Here is a draft. I lenghtened the main hull to 5m. On light winds the boat would have most of the weight on it anyway. The top and bottom side of the floats would be like mirror images so that I could make all four hull panels in a single mold. The resulting shape would also give much volume for minimum surface area.
     

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  2. kerosene
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    kerosene Senior Member

    Hi TTTP,

    You mention kayaking - would you consider something that would be more of a touring kayak with floats? You should check Triak if for nothing else just for inspiration.

    About books - I think elements of boat strength has been criticized for its "rule of thumb" style equations for scantlings that end up being fairly inaccurate.

    One book you should definitely check is the gougeon brothers on boat building. Good reference book about working with epoxies and there are some interesting techniques. One method that you might want to look into is the "tortured" or "compound" plywood frames. They have made amas for big tris like this - you need to work your design with a scale model as its hard to predict what you can actually do with the method (ie. cad is out of question)

    Finnish birch plywood is quite cheap material back there and while birch is not the most rot resistant with a epoxy capsulation and if the boat is stored of the water it would work fine (I think...)

    I'll try to find pictures of the tortured plywood technique.

    Heikki (thats right - I am from up there though live in California these days)



    Triak:
    http://www.triaksports.com/design/

    I think this is interesting technique - compound bottom piece is joined to plywood topsides . Unfortunately there is no reference to the method used for the bilge part.
    http://home.earthlink.net/~ritakend/sitebuildercontent/sitebuilderpictures/float_pan_bond.jpg
     
  3. kerosene
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    kerosene Senior Member

  4. Chris Ostlind

    Chris Ostlind Previous Member

    TTTP,

    I like where you have gone with your design. It is clean, simple and to the point.

    Couple of things about tris of this size:

    1. Try to get as much ama volume well forward, as you can. If this means lengthening the ama, then do it. These boats, especially with assy spinnakers for offwind work, will really want to get tossed over their leeward ama bow. Having the ama volume so far aft will enhance that characteristic.

    Secondarily to this topic, the bow of the vaka, as pictured, is probably not going to give the needed buoyancy up front, if you wish to push this boat beyond casual sailing.

    2. Crew weight and placement while sailing are critical as the weight of one adult is very nearly the total weight of the boat itself when ready to sail. Make sure that there is plenty of room to move about the boat while sailing. This will give a huge amount of flexibility for the skipper as to how the boat trims when underway in differing wind and sea state conditions.
     
  5. oldsailor7
    Joined: May 2008
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    oldsailor7 Senior Member

    TTTP.
    You have had a wealth of information on the thread so far, and most of it is excellent. But I am wondering if it is too advanced for you.
    We do not know how much sailing experience you have,and you say your BUILDING experience is zilch.

    Perhaps you should start to walk before you can run and keep this whole first project simple.

    Like a Piver "Frolic" 5M, for instance. You can still get the plans. It is built from sheet ply using the wood/epoxy technique, and would give you a rapid learning curve in both boatbuilding and multihull sailing.

    With it's self tacking jib and excellent turn of speed it would enable you to get the experience you need and then move on-- without costing you an arm and a leg. :eek:
     
  6. Capn Mud
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    Capn Mud Junior Member

  7. Capn Mud
    Joined: Apr 2008
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    Capn Mud Junior Member

    NACA Profiles

    Chris,

    Where can I find the coordinates for these. My searches of this site and web in general have not succeeded this far.

    Thanks,
    Andrew
     
  8. oldsailor7
    Joined: May 2008
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    oldsailor7 Senior Member

    Chris said--"NACA 0000 profiles are very good all-around foil sections and are pretty easy for home builders to complete. For a daggerboard/centerboard on a boat such as this one, I suggest a NACA 0009 section. For the rudder a NACA 0012 is a very good solution. Neither of these foils are going to give you that last knot or two in high speed use, but they will function extremely well in low-to-mid speed work."

    I couldn't agree more for a cruising boat which isn't going to be pushed.

    However for a boat which I am going to be using for racing as well as cruising--- I use NACA 0008 for the daggerboards/centreboard and 0009 for the rudder(s).
     
  9. Capn Mud
    Joined: Apr 2008
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    Capn Mud Junior Member

    NACA Profiles

    Oldsailor,

    Hmmm OK - but where can I find the profiles themselves (or am I being particularly dim in asking)?
     
  10. deepsix
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    deepsix Senior Member

  11. Capn Mud
    Joined: Apr 2008
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    Capn Mud Junior Member

    Thanks a bundle...... Took me awhile to realise that you get different NACA numbers by varying the thickness parameter..... Am I slow or what!! :-(
     

  12. Chris Ostlind

    Chris Ostlind Previous Member

    This page has, specifically, those two sections (0009 and 0012) as downloadable .gif images. They are already sized for different chord dimensions and you can simply print them out. If you wish to get really creative, take the printed page to a nearby copying machine and scale them accordingly. Images below.

    http://www.my-town.com/sailing/foils/rudder.htm

    I typically make a set of plywood templates to aid in the shaping of the core. I enlarge or reduce the section drawing to suit the chord at 4-6" intervals along the immersed blade, depending on length of the foil you are making. I do not like to use plywood for the cores, even though the revealed laminates make for really nice guides for sanding to a constant angle. Instead, I prefer to use red cedar or, if you can get it, Sitka Spruce, laid-up from many pieces with the grain alternating from head to tip. I glue-up the core with resourcinol, or epoxy.

    Foils are fun to make as there is a degree of sculpture involved in the shaping if you do it by hand.

    Chris
     

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