Do CAD format Boat Plans still require Lofting?

Discussion in 'Boat Design' started by Gerhart, Mar 29, 2013.

  1. pdwiley
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    pdwiley Senior Member

    I agree completely. With steel plate, I'm pretty happy with a tolerance of 1mm on 4mm plate fits, even 2mm is ok. If the plate has a tight butt fit I'm going to relieve it with a grinder anyway to get proper weld penetration.

    Let's not get confused between *machine shop* tolerances - which is what I was taking exception to - and *boat building* tolerances. There's 2 orders or magnitude, maybe 3, difference.

    PDW
     
  2. PAR
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    PAR Yacht Designer/Builder

    You have an extra zero in there Gonzo and yes, 1/5000th (.0002") is way more precise than a hobbyist can expect. 1% of an inch is .01 (1/100th). .002 is 2 thousandths (1/500th). The hobbyist can expect 10 to 20 thousandths (.01" - .02") and a wood worker can dream of these tolerances, but rarely will get them, particularly when plans only offer 1/8" callouts. This is why you have to fair. On a commercial and professional level, these tolerances aren't acceptable, but this is apples and oranges to the majority of members here. Yes, you can find a 20 million dollar machine, to cut jet engine turbines with amazing tolerances, but this isn't what we're talking about is it? Take a good look at a ShopBot's tolerances, as a brand new machine. I just mentioned this machine, as most know what it is (it's a piece of crap BTW). Let the machine run for a few dozen hours and the tolerances will triple. This means every time the tool moves around, starts and stops, you just picked up or laid down more of this tolerance.
     
  3. gonzo
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    gonzo Senior Member

    Topcoat paint thickness will be about 0.003". Then there is sealer and primer under that. The total thickness will be at least 0.005". For someone to say he will become a "wood butcher" if he can't build to tolerances ten times less is preposterous. Even tolerances within the coating thickness is more than required for an excellent finish.
     
  4. claydog
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    claydog Junior Member

    David,

    You've described the process I work with to a T. I do know of a few cases of clay sculptors moonlighting for boat manufactures, I suspect that all the work they did was on cockpit/interior surfaces. I do use 3D/VR simulation occasionally, those tools tend to be a lot more effective for the interior side of the business, and I primarily work on the exterior.
     
  5. troy2000
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    troy2000 Senior Member

    I suspect clay isn't used more often in boat design because the relatively small number of boats built to any particular design doesn't justify the cost. Whereas a mass-produced car model may be sold in the thousands, I'm guessing most mass-produced boats are sold in the dozens or hundreds.

    McGregor's M-25 had a production run of 7000 over 14 years, and that was enough to land it in the American Sailboat Hall of Fame. In contrast, Ford sold over 600,000 Mustangs in 1966 alone...

    But if I made a living designing super-yachts for the super-rich, you better believe clay would be in my sales arsenal. :)
     
  6. DCockey
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    DCockey Senior Member

    The materials and equipment for clay modeling are relatively inexpensive, particularly for smaller models. Whether the cost is justified depends on how important a physical model is, and what the alternatives are.

    The clay used is industrial modeling clay and in the US the major source is Chavant:
    http://www.chavant.com/new_site/files/pdf/Chavan_Catalogue_2012_High_Resolution.pdf
    http://www.chavant.com/new_site/index.htm

    "Clay models" are not solid clay. Rather a thin layer of clay, typically 1/4" thick to 2" thick, is put an armature. The armature has a foam surface supported by a wood and/or metal structure. Clay can also be used to model areas on wood and foam models.

    An oven is needed to heat the clay to around 130F before applying it. Other than temperature control there are no special requirements for the oven. The studios and wind tunnel I was in used restuarant "bun warmers" to keep clay warm for modeling. A large model may need a larger oven.

    The tools used to hand sculpt clay are simple. Room temperature clay is usually sculpted by scraping and carving. If an area needs to be built up additional warm clay is applied and then sculpted as desired.
     
  7. yipster
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    yipster designer

    Clay is nice to work with and did some modeling with it in the past.
    keep it in the pallet. I take it a clay car model nowadays uses a 5 axis foammodel
    that has undergone a few refinement passes like beeing used for boats
    been following this discussion and through the years a few builds
    its the workfloor were a boat is build, sometimes simple and uninformed
    but also with all sorts of cad, cam, 2 and 3d lofts, what you want or have
    than after placing the first plate, whatever it takes to gets that boat of the holy workfloor again
     
  8. wet feet
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    wet feet Senior Member

    I have seen a little clay modelling for cars and it has tended to be directed by the stylists.The character of the car was arrived at by means of pencil sketches or an airbrush image and an outline on the workshop wall,layed out in tape.Having arrived at the first iteration,the engineers got to examine whether all the hardware could be fitted within the envelope and whether it would comply with all the legislation.Any necessary changes were made,often on only one side of the model,and having secured approval the vehicle was digitised.A friend who designs rubber seals for vehicles told me that a variaiton of 0.2-0.3 millimetres can be enough to allow leakage to occur and consequently efforts are made to build cars with less than this amount of variation.
     
  9. DCockey
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    DCockey Senior Member

    Initial concept development starts with sketching, both with paper and on a a computer using software designed for sketching. Some of the sketches are turned into renderings. Then a number of scale "concept" clay models are created based on selected sketches and renderings.

    Next one or two of the scale concept models are selected for further development and refinement. This follows the process I described above in post #70, iterating between clay models, initially scale and then full size, and computer "math" models with increasing emphasis on meeting engineering criteria. A surface would be worked in clay for a while, then scanned. A math model of the surface would be built from the scan, checked against criteria, and modified as needed and desired. The revised surface would be milled into clay for evaluation and further revisions. This iterative process typically would go through many cycles, first in scale then in full size before the surface was released for final refinement on the computer.

    Full size renderings and "tape" side view sometimes end drawings (similar to profile drawings for boats) used to be a major part of the process. (The tape drawings are made with narrow paper and plastic tape most commonly used for creating charts and similar.) By the time I left the industry three and a half years ago the full size tape drawings had been largely superceeded by computer modeling with full size projection of images from the computer models when desired.
     
  10. PAR
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    PAR Yacht Designer/Builder

    David, your description follows what I do. A hand sketch, followed by refinement in Corel Draw, then import into Fast Ship. Of course, I don't bother with clay, but have developed models for various reasons, most often testing.
     
  11. terhohalme
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    terhohalme BEng Boat Technology

  12. troy2000
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    troy2000 Senior Member

    So... let's take a look at what we've learned here.

    1. Some CAD plans need lofting; some don't.

    2. Some builders like to loft anyway; some don't.

    3. Some people like to patronize folks with differing viewpoints; some don't....

    Does it that sum it up pretty well?:)
     
    2 people like this.

  13. Lister

    Lister Previous Member

    1-Well said
    2-Well said
    3-Well said
     
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