Galley Hull Desgin

Discussion in 'Sailboats' started by barbarian, Aug 20, 2012.

  1. barbarian
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    barbarian Junior Member

    I dont know much about boats trying to learn. Im pretty skilled in cad and drafting. Can someone explain me how boat builders draft up the hull of the boat. I know they use a specific method for creating the curves of the hull. Im trying to make an accurate scale model of a galley ship in Alias. How do I model and accurate hull.

    [​IMG]
     
  2. gggGuest
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    gggGuest ...

    That drawing has to be at the least very highly speculative, not to mention controversial.

    Available evidence is extremely scant. The best reference for ancient oared ships is "The Athenian Trireme: The History and Reconstruction of an Ancient Greek Warship" J. S. Morrison/J. F. Coates/ N. B. Rankov (Author), but their reconstruction has been challenged too.
     
  3. barbarian
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    barbarian Junior Member

    I have seen the reconstruction that the greeks did its way off. Can someone show me the method of drawing hull of a normal boat then I will see what I can do about the galley
     
  4. MalSmith
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    MalSmith Boat designing looney

  5. capt vimes
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    capt vimes Senior Member

    software

    another option would be freeship!
    download: http://www.softpedia.com/get/Science-CAD/Freeship-Plus.shtml

    it is freeware and there are several threads on this forum with tutorials to download and such...
    search the forum here and you will get lots of results like:
    http://www.boatdesign.net/forums/design-software/freeship-question-42863.html

    you can actual upload images to the 3 planviews, if you have, and model the hull using the background images for a guidline...
    beware: the images might only be showing the max beam/length and not the interesting parts at the bow or stern... unless you have a full linesplan. ;)
     
  6. DCockey
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    DCockey Senior Member

    Barbarian, some background information about you would be helpful.
    - What is your level of knowledge about boat design and boatbuilding?
    - How much experience do you have with Alias? Have you built other 3D models with it? Have you used spline curves before?

    The illustration you included in your post does not have much information about the hull. I can only determine the profiles in three views from it. Anyone developing a hull model based on that illustration will need to use their own ideas for the rest of the shape of the hull.
     
  7. barbarian
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    barbarian Junior Member

    Ok. I have a Bachelors in Industrial Design Technology, skilled in hand sketching, mechanical drafting and illustrations. Technical expertise , Proficient Photoshop, Illustrator, AutoCad, Rhino 3d, Alias, Solidworks and some understanding of 3d max and vray. Now I have done some studying of classical architecture and and have some know how about engineering but unfortunately I know nothing about boats or boat design or fluid mechanics. I was hoping to do a hand drafting first of the hull then work with it on the computer. As far splines and NURB modeling im proficient can create Automotive Surfaces Class A and do have an extensive understanding of how NURBS and splines work and are crated in CAD programs. A few years ago I went to boat museum and guy there gave me a hand out which explained how the hull of the boat was drafted, the method they use on the three views to create the hull curves but I dont remember any of that. so thats what I want to understand how can I hand draft the hull of the ship, the grid method thats used and how the curves are created. I got a few ebooks on boat building bu they dont explain nothing they are more of a construction related. Based on the three views of the galley how do I draw the splines of the hull?

    [​IMG]

    This is a roughly 1:1 scale 44 meters

    [​IMG]
    [​IMG]
    [​IMG]
     
  8. DCockey
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    DCockey Senior Member

  9. capt vimes
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    capt vimes Senior Member

    i do not quite get it...
    by splines you mean the stations in the bodyplan view - right?
    either you draw them as you feel them fit or you derive them from the plan view where you have drawn the waterlines already...

    either way - you have to start at some point... be it the plan, profile or bodyplan view.
    from there you get all the other lines... check them for fairness and correct if necessary - and then you project those iterations onto the other plans/lines - check them for fairness and correct...
    you said, you have a technical background - see these lines as sections which show up in all three views... the stations now are straight lines in the plan and profile view while curved in the bodyplan view.
    waterlines show curvature only in the plan view and buttocks are curved only in profile view...
    now you get the position of each point on the line by measuring the coordinates from the other views and mark them in the 3rd - draw a line through each of the marked points - check for fairness and correct...

    in the attached image you have an example bodyplan... all horizontal lines are waterlines, the vertical lines are buttocks and the 45° lines are diagonals (which are curved in plan and profile view)...
     

    Attached Files:

  10. sharpii2
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    sharpii2 Senior Member

    OK. Let's start out simple.

    When water, like any fluid, moves around an object, it doesn't like sharp turns. Imagine driving a motorcycle down a road as fast as it can go. Now, suddenly, you encounter a sharp turn. What are you going to have to do? Slow down. That's just what water does when it hits a sharp turn. Actually. it breaks off in eddies, kind of like your motorcycle going off the road, if it can't make the sharp turn. So, you want gradual turns for the water to go around, as it goes past the hull, especially at the bow. At the stern, you can be a bit tighter.

    The reason for this, is because much of the water flow, because of the friction of the hull, is breaking up into eddies, especially if the side of the boat, along it's length, is pretty much a straight line. To have less of these eddies, designers have learned to have a constant curve along the length of the boat, rather than just a pointed bow and stern. This curve pushes the water aside, as the water passes, creating pressure which limits eddies, kind of like a bank in a turn on the road. the tilt of the road keeps your motorcycle on it, because the motorcycle has to go up hill to go off the road. Once the water flow has passed the widest part of the boat, it experiences what would be like a reverse bank in a turn, which tends to help push the motorcycle off the road. But, because this turn is very gradual, the eddies are further minimized.

    Now we don't see very many ships in the harbor with curved sides along their length. This is because the width (Beam) of a ship is limited by practical concerns, such as getting into and getting out of channels, docking, and getting through locks.

    The ship must have enough under water volume to support itself, it's machinery, and it's cargo, so the curve along it's side must be compromised to get adequate under water volume (Displacement). This is one of the very first trade offs in ship design.
     
  11. barbarian
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    barbarian Junior Member

  12. barbarian
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    barbarian Junior Member

    A little bummer . Now how do I blend the buttock lines with the little nudge on the front of the ship

    [​IMG]
     
  13. capt vimes
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    capt vimes Senior Member

    you have to place more points in that area...
    but check your lines - they show now a V-bottom and not the S-bend shape you want to have...
     
  14. capt vimes
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    capt vimes Senior Member

    i attached an image of an example container hull linesplan and the according dxf file... (i hope you can import that)
    although it has not your desired s-bend shape but - as container ships go - a box-shaped hull, it might still give you an idea... ;)
     

    Attached Files:


  15. DCockey
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    DCockey Senior Member

    A buttock is at constant beam. By carrying all the buttock lines to the stern the beam is constant to the stern.

    In planview find the points of the hull edges at the width of each buttock. The corresponding buttock line should pass through that point.

    Sketching sections might be better than buttocks. Decide on the station locations where the sections will be located. Then find the hull edge curve locations at each station. Sketch a set of sections which go through the corresponding points on the edge curves.

    Practice with some simplier hull shapes first.
     
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