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TOPIC: An attempt to draw a J Class

An attempt to draw a J Class 3 years 7 months ago #3858

  • jamessawle
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Thank you so VERY much for this, that PDF is great, looks about the highest res scans I have come across, So VERY much appreciated....

James
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An attempt to draw a J Class 2 years 10 months ago #3952

This topic may well have gone cold over the last year or so. However, I see some general lessons for hull shape re-creation.

Reproducing hull shapes is looming large in my current (and somewhat sporadic) startup with DELFTship.

I would stay away from trying to use AutoCAD or similar for lines fairing from lifted offsets, at least in my present state of knowledge. Get the numbers straight into DELFTship, and use it (a proper hull surface package) for what it is intended to do. A proper hull surface program (as DS) allows ready manipulation of points to control the surface, an propagates all changes automatically.

My first preference in this context is to work off background images. However, reproduction and size (one correspondent quoted an A0 sheet here) can be issues.

If background images are too hard, I suggest markers. I've been using these successfully on recent projects.

For an instance such as a J class I would lift selected offsets to generate curves in both longitudinal (waterlines and buttocks) and transverse (section) directions. Not documented is that marker files can contain multiple lines, crossing and overlapping. I have included 3D lines, with varying x y z point to point (instance a sheer line) as well as the orthogonal lines.

As the Marker facility is generating (undefned) polynomials (I think) between the 3D points, you can place your judgement on the curve interpolations between the data points, and also the fairness/errors in the point values. This latter is significant where you are working from lifted offsets.

I have found the KNUCKLE facility within Markers very useful.

A tip for lifting offsets from a paper sheet. Work to scale.You can do this in at least 2 ways.

The first is to scale the relevant views to one of the industry standard scales (1:10, 1:50 etc, or imperial 1:12, 1:48 etc), and then measure with a scale rule. You scale the prints with a photocopier. It may take you a couple of attempts to get the photocopier scale factor sufficiently close.

The other way is to photocopy your scale rule, and scale the print so it matches the scale of your print.

A great thing about Markers is that if you find your first definition is less than adequate, you can edit your text file (more points, more lines etc), then import the new Markers text file into your DS model.

A strategy I have just hit on for vessels with protuberant keels etc - think small wooden boats, This can sweep up the stem as well.

Model you hull sheer line to rabbet line only; get this right.
Extrude the rabbet line down wards by a nominal amount.
Edit the z values of this new line to generate the keel half siding line.
Extrude this new keel half siding line inwards by a nominal amount.
Edith the y values for this new line to 0 to generate the centre profile line.

If your hull geometry calls for it, you can adjust rabbet line x y z to give a flat surface (no knuckle) at this line - eg up the stem.

This procedure is somewhat idealised, but should give you the gist of the technique. I regard it as a lot more robust (and probably a lot quicker) than creating the x y z for points on the keel half siding and the centre profile lines in the generation of the Markers offsets file.Of course, you wold not need to do this for a J class hull shape.

Peter Edmonds
Naval Architect
Perth, Western Australia
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An attempt to draw a J Class 2 years 10 months ago #3957

  • Maryak
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My J Class modeled in Delfship scale 1:1 from a composite of lines plans downloaded from J Class images site.

Best Regards
Bob
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An attempt to draw a J Class 2 years 9 months ago #3958

  • Jurgen 54
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Hi everybody!
I'm really charmed about this flourish attention on an old topic, even if thoughts on its relative importance never leaved my consciousness.
Now, I'm not interested in pure replicas of old lines nor in mere exibitions of skillness.
What I really meant long ago IS: there is somebody so incoceivably idiot, as me, thinking he can in some way try to REFINE those designes ( please Mr: Dykstra don't laugh SO hard ) jerking with DS on his ridiculous machine and hope to come out with something worth of note???
I let HERE my old file, still untouched by monts, just for start:

Attachment J.fbm not found



So, if you gentlemen are as I expect, get on with: Critics, Proposals, Suggestions, Attachements or Bully me as you want...
Yours, King of Ignorants.
Jurgen.
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An attempt to draw a J Class 2 years 9 months ago #3959

Greetings from Perth, Western Australia

For Jurgen and others, who would like to try to improve on J class boats.

Go for it!

You aren't going to get your design built, given that no-one has been building to J class rules for 80 or so years. Even the much more modest 12 metre has been abandoned by the America's Cup competition.

I hark back to 1990 or 1991 when I was able to sit on on a short Yacht Design course run at University of NSW, primarily for their Naval Architecture students. It was run by Peter Van Oossanen of NSMB fame; at that stage a Sydney resident.

A significant part of our effort went into re-working a Velocity Prediction Program into a flavour of BASIC that we could run.

If you want to design a J class yacht and assess merit, you will have to accept that you will assess merit under a VPP. I have no current information on what is around, but plenty comes up on Google.

You will also need access to the J class rating rules, to be able to determine that your design efforts rate.

One way you could approach this is to design your hypothetical J class yachts as being built in the then contemporary technology - no cheating on weights, CGs, etc.

Another approach would be to design your J class that still rates, but makes use of modern materials, etc. Both approaches could be used.

For this to work you will need to model at least one of the built J class boats. It may be attractive to model at least one of the boats restored and sailing. (I saw them at Cowes, along with the large 12 metre fleet at the America's Cup regatta 2001.) You should be able to get enough from the public domain for a reasonable VPP assessment for at least of one of the current boats.

I await developments and comments.

Peter Edmonds
Perth, Western Australia
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An attempt to draw a J Class 2 years 9 months ago #3960

  • Jurgen 54
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Dear Mr. Peter, thank you for a very encouraging answer...
Better to inform you that my technical skills are devoted to another sector though I was a technical drawer in the age of pencils, china ink and ammonia smelling cyanographies!
All your remarks are indeed of public domaine and I'm aware of the matter ( have a look at the second video posted ).
My goals are a Very small and private: by the time, shrinking a bit here, filing a bit there, still on J class rules, to obtain some models to be tested as a personal satisfaction.
No reboant claims nor immortal fame this time!
But working as a giant rodent, searching every bit of the design for an area of possible improvement, or a chunk of parmesan, maybe...
We'll keep in touch.
Jurgen.
P.S.: Have you solved problems about points and edges?
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An attempt to draw a J Class 5 months 16 hours ago #5194

  • twentytwo
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Hello Maryak,

Your lines look nice! Is the FBM or STL file available anywhere?

Thanks,
Josh
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An attempt to draw a J Class 4 months 4 weeks ago #5195

  • Maryak
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Josh,

I'm sorry but I no longer have the files.

Regards
Maryak
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An attempt to draw a J Class 1 month 4 days ago #5294

  • jamessawle
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Been working on this project now for many months and I have just lost my Hard Drive that had the data on it that Maryak and Jurgan 54 had kindly uploaded, if anyone has any High Res Info on any J-Class Yachts or the FBM to save me recreating this from scratch I would VERY much appreciate someone posting it...

Any help would be greatly appreciated...

James
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