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  #1  
Old 06-10-2015, 11:19 AM
digitalis digitalis is offline
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Interested in Buying or Renting 56 Copenhagen Ship Curves

Hello,

This is my first posting. I'm not so sure this is exactly on topic but please indulge me this once. I was interested in manual drafting since high school 30 years ago and I'm finally acquiring equipment. I have a new Mayline Futurmatic drafting table with a 43.5" x 60" board with a Vemco track drafting machine and a few dozen scales. I have a roll of vinyl drafting board covering material that I will be applying with contact cement and I will be trimming the excess with a router flush trim bit. You get the idea. I'm really serious about getting the right tools which I admit are obsolete. That is my problem. It is hard to get good tools so I search ebay, etsy, etc. I would really like to acquire a complete set of 56 Copenhagen ship curves. If one is not available to buy, I ask if I could rent a set so that I could trace the curves on paper and digitize them so that I can have a set made in acrylic by a local CNC router service. Also, it is my intention to have a box made to contain them. I know trust is an issue so maybe we could work something out so that the lender will not need to worry about his property. I respect tools and you can be sure that I would treat the curves well and promptly return them undamaged. Please email me with an offer. Perhaps I can have more than one set made and I could offer them for sale for someone else interested. Again, I apologize for being a little off topic but this will allow me to work on boat design which is the subject of this forum. I hope to share ideas and communicate with others here on this forum in the future. Thank you, Chris Redding
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  #2  
Old 06-10-2015, 10:16 PM
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gonzo gonzo is offline
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There is no mystery about Copenhagen curves. They are one of many types of sets. You could get French curves and work just as well. Also, it is very common to use objects that have the proper curve. I use splines more than curves.
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Old 06-11-2015, 03:45 AM
TANSL TANSL is offline
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Digitalis is asking for "Copenhagen" curves not French curves.
I gather that what digitalis needs is to draw curves on paper therefore splines (splines what kind?) is not very useful. When you are drawing to scale, for example 1/50, you can not use splines (what kind of splines?, there are several) in many cases, so you need templates curves. This is known by any apprentice draftsman.
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Old 06-11-2015, 04:27 PM
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philSweet philSweet is offline
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They sell a decent set of 6 plastic ship curves at most art and graphics shops. About $15.

Most boats only use one or two curves - that's kind of the whole point. It gives the boat style, and different curves get out different types of boats. Always label the drawing with the curves you used. (But delete this if you publish the lines)
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Old 06-11-2015, 10:33 PM
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gonzo gonzo is offline
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Most draftsmen make their own splines. I still use wood at times, but fiberglass is easily available and works great. Tapered small sail battens are really good for spiral curves.
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Old 06-12-2015, 04:16 AM
TANSL TANSL is offline
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Quote:
Originally Posted by gonzo View Post
Most draftsmen make their own splines.
From WolframMathWorld (http://mathworld.wolfram.com/Spline.html) : “SPLINE a piecewise polynomial function that can have a locally very simple form, yet at the same time be globally flexible and smooth. Splines are very useful for modeling arbitrary functions, and are used extensively in computer graphics.
Cubic splines are implemented in the Wolfram Language as BSplineCurve[pts, SplineDegree -> 3], Bézier curves as BezierCurve[pts], and B-splines as BSplineCurve[pts]. “

I believe, therefore, that it is difficult for any draftsman to make their own splines (by many mathematical background he possesses). Perhaps we are talking about very different things.
I've always had great interest in the work of loftmen and I do not understand this sentence: “Tapered small sail battens”. You could, Gonzo, give any further explanation, please?. Many thanks.
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Old 06-12-2015, 04:18 AM
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Eric Sponberg Eric Sponberg is offline
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Digitalis, Welcome to the forum.

I am retiring at the end of this year, and I have a set of 20 ships curves that I bought when I was a student studying naval architecture at the University of Michigan back in the late 1960s. I'd be happy to sell them to you. It is not a complete set, but these were the essential ones recommended by the Dept. of Naval Architecture at UofM. I also have 2 plastic and 2 wood splines each about 48" long, along with 16 dolphin weights. I also have a quality 48" long stainless steel drafting straight edge, which is more accurate than the Mayline straight edge for drawing grid lines for lines plans. There are other triangles and templates in the drawer. You are welcome to the lot for a reasonable price. You can send me a private message and I can give you more information.

Eric
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Old 06-12-2015, 05:00 AM
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waikikin waikikin is offline
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Quote:
Originally Posted by TANSL View Post
From WolframMathWorld (http://mathworld.wolfram.com/Spline.html) : “SPLINE a piecewise polynomial function that can have a locally very simple form, yet at the same time be globally flexible and smooth. Splines are very useful for modeling arbitrary functions, and are used extensively in computer graphics.
Cubic splines are implemented in the Wolfram Language as BSplineCurve[pts, SplineDegree -> 3], Bézier curves as BezierCurve[pts], and B-splines as BSplineCurve[pts]. “

I believe, therefore, that it is difficult for any draftsman to make their own splines (by many mathematical background he possesses). Perhaps we are talking about very different things.
I've always had great interest in the work of loftmen and I do not understand this sentence: “Tapered small sail battens”. You could, Gonzo, give any further explanation, please?. Many thanks.
Tansl,
Wow, looks like your splines are very complex mathematical modern adaptations of battens that simply tangent through wanted points in a fair fashion. We use/d french curves, paint tins, plastic lids with a squeeze also but splines can be as fine as you need them & would taper slivers of acrylic & wet & dry very smooth.... sometimes we tilt the pencil to interpolate, that is a special skill where the technician communicates the desired line via symbiosis of eye to mind to hand

All the best from Jeff.
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Old 06-12-2015, 05:23 AM
TANSL TANSL is offline
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Regardless of the meaning that can be given to the word spline, for me a spline is a polynomial (second or third degree) and what the loftman uses is a "batten".
Now I understand why a tappered batten is used, I guess to have a variable flexibility.
Certainly a third-degree spline not only ensures that the tangent vectors are the same in each segment linking points, but the curvature in them should be the same. This is the mathematical concept for the term "smoothed" curve.
Indeed, as rightly says TheLoftman, a distinguished member of this forum: "Fairline" A line That is pleasing to the eye !. I think all former professionals will like this definition, which is not as mathematical as mine.
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Old 06-12-2015, 07:28 AM
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waikikin waikikin is offline
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Quote:
Originally Posted by TANSL View Post
Regardless of the meaning that can be given to the word spline, for me a spline is a polynomial (second or third degree) and what the loftman uses is a "batten".
Now I understand why a tappered batten is used, I guess to have a variable flexibility.
Certainly a third-degree spline not only ensures that the tangent vectors are the same in each segment linking points, but the curvature in them should be the same. This is the mathematical concept for the term "smoothed" curve.
Indeed, as rightly says TheLoftman, a distinguished member of this forum: "Fairline" A line That is pleasing to the eye !. I think all former professionals will like this definition, which is not as mathematical as mine.
Well,

Looks like Digitalis/Chris has been offered a very "Fairline" by Eric.... puts him well ahead if he takes it up.
J.
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Old 06-12-2015, 09:34 AM
DCockey DCockey is offline
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Quote:
Originally Posted by TANSL View Post
Regardless of the meaning that can be given to the word spline, for me a spline is a polynomial (second or third degree) and what the loftman uses is a "batten".

.....
In some parts of the world "spline" is the name used for a long, narrow and flexible strip which is used for drawing curves, particularly when used in boat and ship design.

My guess is the mathematical use of "spline" was derived from the use of "spline" described above.
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Old 06-12-2015, 11:08 AM
TANSL TANSL is offline
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It seems that in many parts of the world is assimilated the curve with the object that lets draw it. It sounds good but my opinion is this : In some parts of the world "spline" is the name of the curve drawn with a batten for lines in a boat, a car or anything else, for example, in a vase.
In many parts of the world loftmen have worked many years without using the term spline that was first used when the first CAD / CAM programs emerged.
When someone tried to get the mathematical equations of the curves on the hull of a boat, it was thought initially to use polynomials that define interpolating (interpolation, not approximation) among various points of the line. At first a single equation for the entire line was sought, which led to huge polynomials. Then someone thought it was much more manageable to use many sections of polynomials, linked one to the others, with certain conditions of continuity. A breakthrough was achieved when trying to mimic the operation of the loftmen with battens. Someone thought that a batten was similar to beam subjected to simple bending where loads (the forces applied by the "ducks") were applied. As the deflected beam is a third order polynomial, they decided to use polynomials of the third order with the following conditions:
  • For every two points only would a polynomial.
  • The end point of a polynomial coincide with the start point of the next.
  • The final tangent of a polynomial would be the same as the initial tangent of the following. The initial tangents of the first and the final tangent of the latter define the user at will.
  • The curvature of the two curves coincide at the same point would be the same.
All this allowed to calculate the coefficients of each and every one of the polynomials. The curves thus obtained, I do not know why, were called splines (third grade). As is known, the integral between two points of a cubic polynomial is easy to calculate and therefore allowed a computer calculations were very simple.
Sorry by the "discourse" I've released. It is a subject that I like and where, because of my hobby programming calculations, I had to dig deeper. If this has been of interest to someone, I feel very satisfied.

Last edited by TANSL : 06-13-2015 at 03:17 PM.
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  #13  
Old 06-12-2015, 01:15 PM
Jim_Hbar Jim_Hbar is offline
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Quote:
Originally Posted by digitalis View Post
I have a roll of vinyl drafting board covering material that I will be applying with contact cement and I will be trimming the excess with a router flush trim bit.
Chris - we always attached the vinyl sheet to the table with double-sided tape along the top edge only. Makes it easier to change out in the future.
Be sure to unroll the vinyl, and give it some time (a couple days) to lay flat.
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Old 06-12-2015, 06:27 PM
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waikikin waikikin is offline
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Does the spline define the line or does the line define the spline

Quote:
Originally Posted by TANSL View Post
It seems that in many parts of the world is assimilated the curve with the object that lets draw it. It sounds good but my opinion is this : In some parts of the world "spline" is the name of the curve drawn with a batten for lines in a boat, a car or anything else, for example, in a vase.
In many parts of the world loftmen have worked many years without using the term spline that was first used when the first CAD / CAM programs emerged.
When someone tried to get the mathematical equations of the curves on the hull of a boat, it was thought initially to use polynomials that define interpolating (interpolation, not approximation) among various points of the line. At first a single equation for the entire line was sought, which led to huge polynomials. Then someone thought it was much more manageable to use many sections of polynomials, linked one to the others, with certain conditions of continuity. A breakthrough was achieved when trying to mimic the operation of the loftmen with battens. Someone thought that a batten was similar to beam subjected to simple bending where loads (the forces applied by the dolphin weights) were applied. As the deflected beam is a third order polynomial, they decided to use polynomials of the third order with the following conditions:
  • For every two points only would a polynomial.
  • The end point of a polynomial coincide with the start point of the next.
  • The final tangent of a polynomial would be the same as the initial tangent of the following. The initial tangents of the first and the final tangent of the latter define the user at will.
  • The curvature of the two curves coincide at the same point would be the same.
All this allowed to calculate the coefficients of each and every one of the polynomials. The curves thus obtained, I do not know why, were called splines (third grade). As is known, the integral between two points of a cubic polynomial is easy to calculate and therefore allowed a computer calculations were very simple.
Sorry by the "discourse" I've released. It is a subject that I like and where, because of my hobby programming calculations, I had to dig deeper. If this has been of interest to someone, I feel very satisfied.
Interesting viewpoint Tansl,
My view would be that the word usage predates the "software" revolution & that industry has borrowed the term....
"Battens" certainly are used but possibly the spline adopts a finer profile, the term applies to "wedge seams" also in carvel construction, whether the spline is a line or timber/other that follows such is probably just a language adaptation- special on it's own. My research is not extensive but relates to conversational usage with Shipwright tradesmen over decades, some now passed. The fine battens we used in drawing class at Tafe, here known as splines on cedar drawing boards.... much of our theory classes related to drawing & manual calcs as those with talents in that direction encouraged to further studies in the field.
Nice thread drift, Digitalis hasn't been back yet?

Regards from Jeff.
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  #15  
Old 06-13-2015, 02:42 AM
TANSL TANSL is offline
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I guess on all this influence, not only the nuances of each language, but the nuances of each technical language. In addition, many countries have copied Anglo-Saxon terms, without too rigorous translation. So maybe there are differences in the interpretation given to some words.
Although I have never worked as a manual loftman, I have always admired this profession and have studied their procedures, with great interest, to apply them to my work with CAD. I think one have to know how things are done before asking the computer to do them.
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