Bezier Curve Chine

Discussion in 'Boat Design' started by thesecondwind, Apr 20, 2010.

  1. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    Amen....

    Daniel, it is actually very easy to build a fair hull. My boats built bear testament to that and can be seen in my gallery - should actually update it with more photos.

    A well designed and built radius chine can mimic a round bilge hull and a very well known designer, now residing in NZ once complimented Dudley Dix on his round bilge design in Cape Town many years ago and was flabbergasted when he was told it is in fact a radius chine hull.

    On all the radius chine hulls I had built the radius was constant from bow to stern and only the upper and lower tangents got smaller towards the bow.
     
  2. dreamer
    Joined: Nov 2004
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    dreamer Soñadora

    it makes me think of Bondo. Remember that stuff? I had a friend in high school who bought an old Pontiac Bonnevile with a 'perfect' body and new paint. A few weeks after bying it, he slammed the door shut and a 4" disk of Bondo fell off the door panel.

    Fairing compound is ok in very thin, small doses. I don't think it would work well in this case. I could be wrong. I've never used "boat fairing compound". But somehow I'm imagining a ton of work and after making those small bends on a press, I'd be pretty tired of metalwork at that point.

    But there are guys who are way more committed to hard work than I am. Like the guy making a Colin Archer out of aluminum lapstrake.

    But damn if he isn't almost done with that hull! And it looks awesome.
     
  3. Joe Petrich
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    Joe Petrich Designer

    Wynand, Very nice job on that Dix 43, especially without fairing compound.

    Dskira, I understand and appreciate your commitment to honesty in design and construction.

    In my experience with large custom yacht hulls, (125-240 ft) in steel, aluminum, and fiberglass, there is no way to avoid using fairing compound. If your product doesn't shine like a new Ferrari on launch day, you are not going to sell many. Every top builder in this part of the business uses fairing compound.
     
  4. dskira

    dskira Previous Member

    You are right, and will say, you are unfortunately right :D
    I find a perfect and shiny hull quite wrong, but this my view.
    I want to see the quality of the builder, the character of the boat. the so call defect is part of the real vessel.
    They looks like plastic toy, you even don't know what material they use!
    I am not interested of the performance of Awl Grip and the painters.
    But as I said, it is a very personal view.
    Daniel
     
  5. dreamer
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    dreamer Soñadora

    Joe, I think you are 100% correct (despite my smart alecky comments) with regards to looking extremely smooth. And without question you are more of an authority on boatbuilding than you let on.

    Would this build method require an inordinate amount of faring compound? Have there been accounts of fairing compound failure?

    I met a guy who was building a steel Dix 43. When I met him, he was just finishing the fairing. How long did it take to fair? 2 years. :eek: He had to grind it all off and start over a couple of times.

    I think this whole 'fairing' business is what separates a professional from 'just some guy'. Maybe I'm wrong, but in my mind the most forgiving material fairing-wise to home-build in would be wood (or if you're crazy like Zeyang, substitue aluminum 'planks' for wood).
     
  6. dskira

    dskira Previous Member

    What separate the professional to the amateur is: the professional knows how to weld without distortion, built fair, and keep the hull fair all along.
    The heavy fairing is for yard with lousy workers, who cut corner during the construction, by negligence or ignorance, and please the client for six months.
    I am talking of steel and aluminum building of course. I don't talk about plastic. Which for me is not a marine material, it is a toy material.
    (Please everybody, don't shoot me all at the same time, thanks!)
    Daniel
     
  7. LyndonJ
    Joined: May 2008
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    LyndonJ Senior Member

    Then there are many metal boats that don't need fairing.

    It really comes down to the length of time you can take and the expertise,

    professional buildrers by necessity make trade-offs but a skilled boilermaker with time on their hands or a penchant for perfection can produce hulls like this.
    Note that it's all fully welded ( all frames to plate) and no filler.
     

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  8. dreamer
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    dreamer Soñadora

    *sigh
     
  9. Brent Swain
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    Brent Swain Member

    I've never used a fairing compond on any of my hulls. They are fair enough without it.
    A freind in San Francisco was quoted $40,000 for one of those fancy paint jobs on his totally fair hull. What a total waste of cruising time.
    When a fibreglass boat broker walked into a pub and told one of my clients "Boy , I just saw a beautiful steel boat. It was so smooth, you couldn't tell it from a fibreglass hull."
    My client said "That's too bad. If my boat looked like that, I'd have to get Kenny to weld some rivets on her, so people wouldn't mistake it for fibreglass and think I ws that stupid."
    The fibreglas boat broker turned beet red, with severe culture shock.
     
  10. Joe Petrich
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    Joe Petrich Designer

    Cruisers vs racers, power vs sail, steel vs aluminum vs frp; I just don't understand people who say x material is the only material to build from, or sailboats are superior to powerboats (or vice-versa). Each material has it's own merits and problems. I have found that it's not the type of boat or the material a boat is built from but people and their opinions who cause the biggest problems. I really dislike boat bigotry. Edit: Which is not to say there isn't room for disscussion about methods and materials.
     
    Last edited: May 2, 2010
  11. ancient kayaker
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    ancient kayaker aka Terry Haines

    I use BCs a lot in design, my graphic software handles them nicely, as well as curves based on mathematical formulae. In (wood) construction I sometimes take advantage of the variation of stiffness with thickness of a batten to replicate a formula-based curve, tapering the batten to reduce the number of weights (ducks) required and to get a fairer curve.

    2nd-wind: is that analogous to what you are suggesting? The other alternative that occurs to me is the use of rolling conics to produce complex-looking 3-dimensional shapes with 2-dimensional developments. Other than saddle shapes, neither method is any help for creating true 3 dimensional convex or concave shapes.
     
  12. Brent Swain
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    Brent Swain Member

    Fortunately one can easily design and build a good lookign hull using simple conic sections, which will do any job you want ,without the need for any compound curve. Thus compound curves in a steel hull are more of a gimick or artistic challenge, than functional.
     
  13. dskira

    dskira Previous Member

    Brent you are so dogmatic, you are worth than the one you dislike.
    You are are a pompus *** (do not take that as an insult, it is a way to tell you how narrow minded and opiniated you are)
    When a designer make an opinion, he give a reason of his opinion. You allways make a statement, just a lithanie of complaints and how good you are.
    You say:
    Are you for real? No designer or naval architect will say that, because Brent the compound and reverse curve has a fonction. But you don't know that.
    Or you play the ignorant or you just come from the moon.
    Please wake up, and stop your dogma against things you don't understand.
    Daniel
     

  14. thesecondwind
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    thesecondwind Junior Member

    Ancient Kayaker and to whom it may concern,

    Is it bezier or not bezier, it seems to be a matter of opinion. I think it is close enough to name the construction method.

    Anyway here is the basic design method from the web site.

    In aluminum boat design Bézier curves are used routinely in both traditional hand drafted or computer aided methods. In computer graphics however, Bézier curves are calculated mathematically to connect separate control points to form smooth free-formed curves or surfaces. The advantage of using Bézier curves in computer aided drafting is that they need only a few points to define a large variety of shapes.

    Those who have engineering experience, know that Bézier Curve is the common name used for "free-formed curve." Mathematically they are derived from B-Spline, C-Spline, and Nurb curves. B-Splines and Nurb curves are similar in that the curve itself does not go through any of the interior control points. In C-Splines the curve goes through all control points. All of these curves and splines are useful in boat design.

    There are four curves used to define the hull along its length as shown in Detail A. The top is the Sheer line: the next down is the upper longitudinal line; followed by the lower longitudinal line; the last line is the fairbody line. All of these lines are C-Curves. This means that the curve goes through its control points. These lines define true Bézier Curves

    The upper and lower longitudinal lines in this aluminum boat design are placed at predetermined locations in the hulls longitudinal framing system. They are located at the point of tangency where a smooth transition takes place between the upper developable surface and the true round section of the hull. This is also true of the transition between the true round section and the lower developable surface. Between the upper and lower longitudinal curved lines are seven B-curves used to control the shape of hull between the developable surfaces.

    Picking any one of the B-curves for reference, see (Detail A1,) notice they have three (3) control points each. The top and bottom points are locked to longitudinal curve on which they lie, while also controlling the shape of the longitudinal curve itself. The middle control point of the B-curve is placed to maintain a tangency between the upper and lower developable surfaces.

    These seven Type 2, B-curves used in this aluminum boat design to support a C-lofted surface, between the upper and lower developable surfaces. With the C-lofted surface being non-developable, a series of developable sub-surfaces are superimposed or layered over it.

    To create developable sub-surfaces, magnets are used, which are required to lie on their assigned C-lofted surface. By placing the magnet entities, the designer defines the size and location of the developable sub-surfaces.

    With the magnet point entities in place snake curve entities, which also required to lie on their assigned surface, can be created using the magnets as support. Two adjacent snake curves provide support for the developable sub-surfaces.

    A total of thirty-five snakes are used, dividing up the length of the surface at the turn of the chine into thirty-four developable sub surfaces.

    Detail-B shows a developable surface, (in blue), overlayed over the host C-lofted surface.

    In Detail-C below we can see all the entities. The type 2 B-spline curves which support the C-lofted surface, the magnets assigned to the C-lofted surface, the snake curve entities, and the developable sub-surface.

    All the sub-surfaces are then developed to create a flat pattern, to be cut from sheet material. After which the metal patterns are formed in a press break back to a three dimensional hull plating section. They fit seamless to the hull framework. Resulting in a true round hull.

    Dennis
     
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