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Author Topic: drawing a 'flat' shape from a 'curved' original.......how???  (Read 3807 times)

carlmt

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drawing a 'flat' shape from a 'curved' original.......how???
« on: January 10, 2011, 02:14:47 PM »

Can anyone help with this conumdrum?

Trying to create a 'flat' shape from a plan and side view of a curved superstructure element. Not only is it curved from beam to beam around the stern of the boat, but it also slopes from a lower deck to an upper one.

I know the total length of wall line at each deck level and the overall height along the slope of the panel. What I need to work out is the true shape of the top and bottom of the panel along the deck edges.

If i draw a flat length with parallel sides representing the deck edges, when it is curved from beam to beam the centre of the panel lifts from the deck. Therefore, the panel needs a curve along its bottom and top edges so that it sits squarely on the deck (am I making sense?)

The panel I am trying to draw is the rear curved one in the photo below - the one with small windows in it.

Anyone have a graphical or mathematical way of doing this?
Cheers

Carl

Pat Matthews

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #1 on: January 10, 2011, 02:39:43 PM »

There are certainly techniques in manual drafting and in CAD to develop such flat patterns. But the easiest way for a modeler is to build the two decks, then just wrap some paper around the edges, and trace the edge with a pencil. This also eliminates any error developed by the actual model shape varying from the perfect plan...

Depending on the situation, you might be able to wrap a single sheet around... or you may need to tape together many scraps of paper...
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carlmt

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #2 on: January 10, 2011, 02:45:22 PM »

Cheers Pat - that is exactly the advice given me this morning by an architectural illustrator freind of mine!!!!

I just maybe thought that there might have been a method or two used by some on here when designing from scratch.......

will probably do as you suggested........
Carl

BarryM

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #3 on: January 10, 2011, 03:17:23 PM »

Carl,

When I have done this I have mocked-up the superstructure using scrap polystyrene packaging. If you can't find a bit thick enough, stick a few bits together. Carve and sand it to shape and then lay a piece of thin card across it and trace the edges as suggested, to get the shape. 

Hope this helps.

Barry M
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kiwi

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #4 on: January 10, 2011, 05:51:14 PM »

Hi,
There is indeed a method of developing curved surfaces, but in your case, much easier to do as advised, and wrap a sheet around and mark.
Basically, for a curved surface similar to the one in the photo, the development needs to be done perpendicular to the wall on the elevation. This will give you the top & bottom curves, assuming the angle to the vertical is constant.Developing curved surfaces manually is a real art, especially if the slope angle changes. If you want to persist drawing it manually, I suggest getting a suitable book on the subject and practice for a day or two.
However, you could build a fair amount of boat in a day or two using the paper wrap method.
cheers
kiwi
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Umi_Ryuzuki

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #5 on: January 10, 2011, 07:40:56 PM »

You want to draw a conical section, there is math to that, and formulas.
I keep a book around with all those formula, but it may be easier to use an app.

http://www.rocketreviews.com/tool_shroud.shtml

The issue then becomes, how do you draw the large arcs you will need, as
no compass typically can be expanded so large. Maybe a meter stick with a couple of pencil attached?

Paper and pencils held and drawn in place are the quick solution.

 O0
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hollowhornbear

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #6 on: January 10, 2011, 08:26:41 PM »

From a plan view (i.e from above) and a side elevation, assuming the curve is constant and angle constant then the parallel line method of pattern development can be used, if the angle changes which i suspect it will, then you need to us triangulation, to plot the various heights in relation to chord points on the curves, bet you wish you hadn't asked now.  :-)
so to put it simply use the card and pencil method.  :-)) :-))
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carlmt

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #7 on: January 10, 2011, 09:16:57 PM »

Thank you all for your excellent suggestions....

Umi - size of drawing is not a problem for me as I use AutoCAD on a laptop and draw at 1:1 (full size) then plot to the required scale (1:96). The calculator works well, but only for true cones - the rear structure in question has a constantly changing curve at each deck level......unfortunately!!!!!

My use of CAD is restricted to 2D only and not 3D......

Having given it some considerable thought today I maybe think I have found a way...........but I will still check it out by the 'paper wrap' method...

Hollowhornbear - I think this diagram is close to what you are trying to explain?

Carl

The Loftsman

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #8 on: November 16, 2011, 10:38:05 PM »

Hi Carl,
Seen this post and had to reply, what you are trying to do is known as Lofting, a task that used to be carried out by a Loftsman, and it is a little bit more involved than you may think as you would be dealing with true expanded lenghts and trying to develope this shape, across a camber and perhaps with sheer fore and aft as well, it is way too involved to go into here and dont think it is something you could crack in a couple of days, should you go to the trouble of trying to find a decent book on Lofting, or "The Geometry of Shipbuilding" you would be able to do it in CAD, but would have to agree that wrapping a sheet of thin plastic (Mylar) if you can find it and in effect creating a template from your model may well be the best way for you to go.
Take a look at my website at www.leithshipyards.com  and you will be able to find out more.

Good luck

The Loftsman
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Shipmate60

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #9 on: November 16, 2011, 10:49:45 PM »

Can you get the "Shell Expansion" drawing for her and all the shape of the plates are drawn as flat.

Bob
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carlmt

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #10 on: November 16, 2011, 11:40:55 PM »

The Loftsman - thankyou for your considered and helpful advice, I will most certainly look out for those books you suggested as I am very keen to try and expand my knowledge and skill in this dicipline. It may well take years, but it is something I want to do........I am fed up with drawing buildings - too regular!!!!!  I have bookmarked your website also for an enjoyable read this weekend when I have a bit more time.  In the sort term, I have resorted to building 1:48 scale mock-up models of the areas of superstructure in question an doing as you suggested, albeit with card, and forming a template of the part needed. This template is then scanned into the computer, scaled within AutoCAD, and then inserted into the master drawing of the ship. It seems to work so far!!!!

Shipmate - unfortunately, the shell expansion drawings for Free Enterprise V are long gone......... The only accurate drawings I could get hold of were the latest General Arrangement drawings prepared by a firm of naval architects in Scotland for the classification society. Luckily, they were prepared on CAD!!

Carl

The Loftsman

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #11 on: February 18, 2012, 12:36:13 AM »

Thanks for your interest in the site Carl,
Bye the way the "Shell Expansion" drawing would do you no good as this was just a pure roll of the lenght around the frame stations and not the expanded lenghts, this has to be developed out.
Good luck with your model and if you get it finished send some pics to the www.leithshipyards.com website and we would be pleased to show them on the site.

Cheers
 
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David 48

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Re: drawing a 'flat' shape from a 'curved' original.......how???
« Reply #12 on: February 18, 2012, 09:26:16 AM »

There isDelftship have you seen this  it might be of help . I have tried it it is good understand how lofting works and you can play around and alter ships lines .
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