Boat Building Projects Underway

Discussion in 'Boatbuilding' started by Manie B, Sep 29, 2009.

  1. amariner
    Joined: Mar 2011
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    Location: ukraine

    amariner Junior Member

    Ray, Of course, you have to make stability calculation if you are going to use sails. Do you have any boat drawings and mass calculation? WHere to are you going to put the ballast?
     
  2. RayThackeray
    Joined: Apr 2011
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    Location: Alameda, CA, USA

    RayThackeray Senior Member

    Ballast

    As mentioned in my original posting, my keel is still empty. There are two sections I can add ballast, they average about 30 inches wide by 6 feet long and 5 feet deep, so room for many tons.
     
  3. amariner
    Joined: Mar 2011
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    Location: ukraine

    amariner Junior Member

    what is your boat present displacement?
     
  4. RayThackeray
    Joined: Apr 2011
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    Location: Alameda, CA, USA

    RayThackeray Senior Member

    Displacement

    Still to be determined. I even spoke to the Yard owner, apparently no record though he thinks about 50 US Tons. She was splashed once to test welds and write the waterline, which is marked and she looks light, I'm happy to put a lot more weight aboard and bring the line down another 4" or so, however that would get down to the midships port and starboard scupper output pipes, which are an inch proud.

    How should I take it from here? I have no plans and understand it may be difficult to contact the previous owner/builder though of course will try! I plan to model her in Google SketchUp which looks fantastic - would that be useful to a marine architect?
     
  5. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    To establish real stability figures a naval architect will have to model the hull and deck in a hydrostatic program.....FreeShip+ is a start and it's available for free download.....beyond the hull model you will also need to establish a vertical center of gravity (which requires a weight study or wait until she's launched to do an inclining) and working displacement.......none of this is simply explained in a short post....see my posts in this thread.....http://www.boatdesign.net/forums/stability/swain-bs_36-stability-curve-37070.html
     
  6. RayThackeray
    Joined: Apr 2011
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    Location: Alameda, CA, USA

    RayThackeray Senior Member

    An Inclining

    Hi Tad, many thanks, you confirm things I already suspected, this is my first time through with a new boat. Thanks also for the pointer to FreeShip +, I'll have a look, perhaps I can do some preliminary stuff myself.

    I'm suspecting that most likely testing will need to be done when she's in the water, as she's a custom design with no plans (not that I've found so far anyway...!)

    Could anyone explain what happens in an "Inclining"?

    Here's a rough picture of what she should look like with a reaching rig from SketchUp touched up with Photoshop.

    Cheers,

    Ray

    T2 Starboard RigPainted.jpg
     
  7. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Ray: I've not done this but it should work in theory.

    Run tape of contrasting color along the centerline and waterline. Apply more tape vertically at the stations in 11 or so equispaced locations from midships to stem and stern. Measure the station spacing. Add short pieces of tape across the station tape, a pair to each station, precisely 1 foot apart or whatever is convenient for later scaling.

    Now take photos from ahead and astern. Print the photos measure the distance between the 1 foot markers on each station and scale a copy for each station so the marker spacing on that station are spaced conveniently for scaling, say 1 inch; use the largest possible scale for accuracy.

    Now for each station you can measure from the waterline and centerline to establish XYZ offsets. use digital calipers if you have them. Placed into a properly formatted table, these can be input directly into FreeShip, which will provide displacement, metacentric height and cross curves. The data will not be exact but should be close enough for the purposes of establishing the optimum working displacement and ballasting, aproximate CoG location and suitable rig size.

    If you have a laser level with a line output you may be able to use it instead of tape, taking a photo at each station, but you will need something on known length in each picture for scaling and the waterline should still be taped to provide a horizontal datum. You may have to work at night or around dusk, it will need some experimenting to refine the method. Don't see why it wouldn't work though.

    Also read Eric Sponberg's papers at http://www.boatdesign.net/forums/bo...ulation-implications-30857-18.html#post353422
     
  8. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Google Sketchup is a complete waste of time if you have to do curves like boat hulls - its great for buildings and angular projects like trailers etc.

    Ancient Kayakers suggestion is a great one - its the best way to start.

    Dont be too disappointed if you find that you just cannot do the conversion - just enjoy the boat. You have a long road ahead to just to the calculations done, and in the end you may find it just not practical. Its like jet pilots - you have to rely on your instruments, you cant go by 'the seat of the pants' feel.
     
  9. McHale
    Joined: May 2011
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    Location: Western AUstralia

    McHale New Member

    Inclining

    An inclining experiment, briefly the purpose is find the ship's vertical centre of gravity in an axial cross section that sits at the longitudinal centre of gravity. Got that? OR it lets you calculate the "side to side" centre of gravity at the ships fore and aft centre of gravity. What happens is large pendulums are set up in an enclosed or semi enclosed area, the draughts are carefully measured, water temperature taken and then the experiment can begin. Known weights are moved from the centreline of the ship an exact distance and the angle of the pendulum is recorded. this is repeated for various combinations of distance and weights. From this the marine architech can calculate your ships centre of gravity (roll point) and thence your stability curves. Of course all this is dependant on the architech having a set of ships plans to assist in calculations! No plans - no stability calcs - no stabilty curves. Oh, and the weather has to be just so, winds below 6 knots and almost a millpond. Now having said all that someone else can come along and correct me.
     
  10. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Sounds perfectly correct except I don't see what part the ship's plans would play in that procedure. If the weight and distance - hence the moment - is known and the angle is measured you have the righting moment at that angle. No more calculations needed. For a sailboat that has a mast of adequate strength and a place to moor the boat at stem and stern a spring gauge and a protractor is enough. There's a thread somewhere in the bowels of the forum where somebody does that in a marina. In my canoe I can just swing the paddle off to one side . . .
     
  11. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    The fundamental stability formula is...... BM = I/V

    B is the center of bouyancy
    M is the Metacenter (about which B is shown to rotate)
    I is Inertia of waterplane
    V is volume (displacement)


    Stability changes with differences in V (displacement) ......your canoe will have slightly different stability depending on whether there is one, two, or three people in the boat......Having the hull lines and floatation measurements you can calculate the displacement at any loading....and record the stability (derived from the inclining) at that load condition.......So the NA can say stability (in GZ feet, metres, righting moment, whatever) is such at this draft and trim.......
     
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  12. themanshed
    Joined: Sep 2009
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    Location: Palm Beach County

    themanshed Senior Member

    I've posted a few times. My project is a Kurt Hughes 20' trimaran that I had Kurt modify and redesign for composite materials of foam and carbon. My website is www.themanshed.net left upper side TMS-20. Few pics over the build...
     

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  13. Nurb
    Joined: Jan 2011
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    Location: IL

    Nurb Junior Member

    Nice documentation of the build and an interesting boat. Will be following with interest.
     
  14. rsimon
    Joined: Jun 2011
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    Location: Land locked Florida

    rsimon Junior Member

    Just signed up to Boatdesign forum site

    "Casa Cayo" has been a real project! I've been doing most everything myself with very little help (except from welders.) It's been 5 years and I thought I'd be further along than I thought I would be. The forum has helped a lot though and look forward to perusing the ongoing boat projects. I'm looking for a good used outboard->Evinrude (HP range 140~200) with an extra-long shaft.
    2 stroke preferable, has to be one that has been maintained properly though.
    Here is my project, a 1969 Marinette Rivercruiser houseboat...every inch aluminum...light weight (approx 7000lbs) and built like a tank. Estim. 28" draft.
    The unexpected surprise of horrible corrosion (as you will see) caused a lot of delay in the project. I post updated pictures regularly, Just yesterday I bolted up the generator enclosure box on that shelf hanging off the stern/transom area (the most recent picture) check it out:
    http://s1216.photobucket.com/albums/dd377/projecthouseboat/
     

  15. rsimon
    Joined: Jun 2011
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    Location: Land locked Florida

    rsimon Junior Member

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