An attempt to draw a J Class

DELFTship forum Hull modeling An attempt to draw a J Class

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    • #36894
      giorgio zuppin
      Participant

      Let’s try again: My previous post about it was a bit disconcerting in the title – Skipper got an EPIRB… – my fault.
      I use to write with less drama and more fun.
      Anyway, the topic is about a Great sailing boat class design and the attempts to re- create, -invent, -interpretate it.
      I must admitt with a sense of frustration, that the task is difficult, the sheer abundance of 3D curves swelling up, down and sideways of that mighty boat’s hull is unnerving.
      Compared to a contemporary design of a VOR racer, it’s like a snakeprint V/S an armchair…

      As you can see I’m keeping on but, please, Any suggestion and/or useful tip from someone who as tried the same task yet
      ( I refuse even to think, nobody had… ) will be very helpful; best tips could be how to evaluate – remaining in DS – the progresses on small hull refinements and the leaned hull attitude.
      Again, many thanks.
      Jurgen.

    • #36909
      giorgio zuppin
      Participant

      Last developement:

      Underwater lines in profile, similar to British design of 1934, the approach to keel lines is more radical than contemporary designs.
      I try to reduce drag leaving round lines at the beam.
      Any comment and/or suggestion warmly welcomed.
      Cheers, Jurgen.

    • #36912
      giorgio zuppin
      Participant

      Hey! No, its’ not stalking, please.
      I just realized that most of you maybe do not know what I’m talking about,so here is a useful link:

      http://www.youtube.com/watch?v=irmfc3uDGTs

      Enjoy, and maybe you’ll understand my obsession.
      Jurgen.

    • #36913
      giorgio zuppin
      Participant

      And here’s another specially for our dutch webfans:

      http://www.youtube.com/watch?v=If35AoCDt80

      again, enjoy it.
      Jurgen.

    • #37336
      James Sawle
      Participant

      Can I please ask where you got the line drawings from for the J-Class’s, I have been looking for a reasonable sized jpeg just for this reason but not had much hope, I ordered a set from Cormwall Model Boats, but this came as an A0 Sheet, and I have tried with little success to scan the drawing and stitch them together, but it is not working!

      Great work by the way

      James

      PS. I have sailed on Valsheda 3 times now.

    • #37339
      Robert Holme
      Participant

      Hi James and Jurgen,

      My approach to this is labourious but works. Take measurements with a ruler and transfer the body plan into cad.. From there it is a fairly easy process to create a bmp/jpg. The attachement was done from an AO and an A3 blueprint.

      Hope this helps.

      Best Regards
      Bob

      Attachments:
    • #37343
      giorgio zuppin
      Participant

      From the official J class site you can purchase them and carefully searching the web there are fragments of The Book itself.
      Thank you but looking carefully it’s a mess…
      YOU LUCKY XXXXXXX !!! You mean ON BOARD… Envy, envy, envy…
      An angry salute, Jurgen.

    • #37347
      Robert Holme
      Participant

      Attached is a Freebee I found on the net of replica Intrepid.

      Best Regards
      Bob

    • #37348
      James Sawle
      Participant

      Thanks for that Maryak, much appreciated, though the hull design is a lot different to that I know, but it will be a good starting point to see if I can create a hull from.

      Thanks for the good find…

      James

    • #37349
      giorgio zuppin
      Participant

      Here it is Mr.James, in .pdf for better resolution – .jpeg in DS lose some bytes –
      A batch of images of pre-war boats: plans are easy to export as background.
      I want a pic of you shinin’ the brass on Velsheda!
      Bye, Jurgen.

    • #37350
      James Sawle
      Participant

      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

    • #37460
      Peter Edmonds
      Participant

      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

    • #37470
      Robert Holme
      Participant

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

      Best Regards
      Bob

      Attachments:
    • #37471
      giorgio zuppin
      Participant

      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:

      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.

    • #37472
      Peter Edmonds
      Participant

      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

    • #37473
      giorgio zuppin
      Participant

      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?

    • #38876
      Josh Peck
      Participant

      Hello Maryak,

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

      Thanks,
      Josh

    • #38877
      Robert Holme
      Participant

      Josh,

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

      Regards
      Maryak

    • #38982
      James Sawle
      Participant

      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

    • #39018
      James Sawle
      Participant

      Managed to get my files off my Hard Drive by sending it to a lab in Ireland, so for anyone interested here are some files on the J Class Hull design that you may find useful.

      https://rg.to/file/ac7866c8f8e305324dfae5a8b3c0b242/J_Class.zip.html

      James

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