How long does it usually take for you to ...

Discussion in 'Software' started by ldigas, Mar 23, 2012.

  1. ldigas
    Joined: Feb 2011
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    ldigas Senior Member

    My coleague and I were having a long discussion today (since it was a first sunny day in months, we decided to spend a good chunk of its afternoon in a local brasserie :) so I thought I'd ask you for your estimate.

    After receiving a lines plan with a table of offsets, not corresponding in a lot of places to the lines plan (the paper deforms with age and with humidity is one of the possible reasons) ... how long does it take you to fair it and make up a 3d model (in your preffered software) from which frames can be extracted and a lines drawing can be plotted?

    My estimate was something between 2 days and a week (5 working days), depending on the complexity of the given assignment (most often the superstructure) ... am I far from the usual time it takes to do that? Is it something that is done within a day or two, or ...?
    (talking about most vessels that fit within a 15-40m category)
     
  2. daiquiri
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    daiquiri Engineering and Design

    It can be very fast process if you are proficient with the software you have. 2 workdays is quite a reasonable and safe estimate.
     
  3. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Yes, but you might be able to charge for 4 days, thereby getting 2 days of "paid" sailing. :)
     
  4. daiquiri
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    daiquiri Engineering and Design

    Now I see that it works the same way in every part of the globe... ;)
     
  5. DCockey
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    DCockey Senior Member

    Depends on the shape of the hull, the quality of the offsets, how fair the 3D model needs to be, and how close to the original design shape is required. Note that the last two can conflict. Also as diaquiri noted it depends on proficiency with the software and how to model the particular boat shape with it.

    My experience is with small boat hulls. I can input a table of offsets in 20 minutes to 1 hours as points into Rhino using an Excel spreadsheet template I created. The initial 3D model usually takes less than another hour. After that it depends on the factors listed above, and can take anywhere from another hour to several days.
     
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  6. ldigas
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    ldigas Senior Member

    What do you mean when you say "how close to the original design shape ..."? I mean, you have a lines plan and a table of offsets. That's your only input. So, you make it as fair (as your eyes can perceive) and so it fits those parameters.

    There is always a possibility that the (for example, an already built boat) deviates from those offsets, but that is not your problem - if you were not given any measurements from the yard.

    Interesting, I wasn't aware of Rhino's capabilities for connecting with Excel. Could you put up a few words on that?

    My way of doing it was always via Rhino's macro files.
     
  7. DCockey
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    DCockey Senior Member

    How close to the offsets does the surface need to be; 0.2 mm, 1 mm, 5 mm? It is easier and quicker to fair when the allowed deviation is larger.

    I've seen some 3D models claimed to be developed from offsets which have major deviations from the offsets after "fairing".

    PointDeviation is a good tool to use in Rhino to check how close the surface is to the input points.

    Put the offsets into an Excel spreadsheet along with the waterline heights, buttock half-breadths, etc. Re-arrange on a sheet so they have one point per row with corresponding x,y,z in columns A, B, C. No other rows or columns on the sheet. Save the sheet as a .csv file or .txt file. Import the .csv or .txt file into Rhino.

    How do you do it with Rhino macro files?
     
  8. DavidJ
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    DavidJ Senior Member

    I completely agree with Mr.Cockey on this one. If it is a simple hardchine hull and accuracy isn't terribly important I can have the model done very quickly. If the linesplan is already in the computer, say in autocad format, it only takes minutes to move the sections into position, rotate them, and run surfaces through the curves. I've gone from lines plan to 3d model of double ended ferries in less than an hour. That's about as easy as it get. Both ends are the same so you only have to model a quarter of a boat and they are built in the simplest way possible. If I was trying to win a contest for the quickest hull and the lines plan didn't need cleaning up I could probably make the hull in 10 minutes.

    It can also take a few days to make the model if there is complicated hull geometry. Making a perfectly faired bulbous can be difficult. Or say a hull that has lots of shape. A simple hull will only need the body plan to make an accurate model but a hull that has hollows in different directions will mean you need to fair it in more than one direction. I am having trouble explaining this but basically like hand drafting you can make a surface that hits all the points in the sections, but misses the waterlines or buttocks. It takes a lot more work to line up all the lines.
     
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  9. Ad Hoc
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    Ad Hoc Naval Architect

    Not sure what you mean by that, can you explain?

    Since offsets, used by the shopfloor, is their guide to the hull shape for making templates. They, the loftsman (in the old days anyway) would fair the lines from the offsets. If there is a deviation in shape...so what?..so long as the lines are fair for production. Offsets are never guaranteed to be perfectly fair, some are most are not. That was the point of a mould loft. Before pesky computers came along ;):eek:

    On the other side of the coin. Ive seen so called "faired" lines from software and it is a pig...lines like donkey's hind legs. Faired lines from software can be just as "unfair" as manually generated one, even if the computer says "it's fair"!!

    It is the skill, or rather an art, of the person creating the lines that understand 3D shapes and fairness. No computer program can tell/teach you that.

    I recall several years ago when ShipConstructor came to our office trying to punt their software. They gave us a big full-on presentation. When they were showing how/where lines come from....our "lines man" at the back piped up...er...sorry..your hull is not fair. What??....you're mistaken, it is. So bless him, our dear man got up and went over to the large monitor and pointed out where it was not fair. The shipC man was puzzled....had a few looks squinted his eye...hmmmm...im sure it is. His colleague piped up...er....yes, you're correct, it is not 100% fair. The software couldn't get that part of the hull right. No one has ever spotted that before! :p
     
  10. ldigas
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    ldigas Senior Member

    Ah, yes. But that is a bit contradictory, for
    a) either the surface is gonna be fair, or
    b) the surface is going to lie exactly on the offsets (never a problem to accomplish) or
    c) the surface is going to lie exactly on the offsets, and it is going to be fair, just not quite as much as in a)
    d) the surface is going to lie exactly on the offsets and it is going to be perfectly fair <- this occurs very rarely when I'm doing it :)

    Now the problem with this approach, is when you (well, not "you" personally, but somebody ...) say the surface needs to be let's say, 0.2mm - is that it's pointless. If the surface needs to be that close to the offset points in question, then it is probably a mold build (I see no need for such technological requirement for hulls built out of metal or wood; wood "works" (expands/shrinks) by more than that ...

    So I take offsets and fair them up into a nice surface. But, what are the chances that my surface in other parts (between the places measured and whose offsets are given) will be the same. None. Unless I'm, or should I say the builder, is given the original 3d model or a table of offsets with dozens/hundreds of values, so that he can replicate the model exactly.

    Who hasn't :)
    Yeah, well ... blame it on the file formats conversion ;)))

    Ah, I see ... so it's more of a csv/txt Rhino connection, so to say. I was hoping for some sort of Rhino/Excel's VBA interconnection, which I'm sure exists via Rhino scripts, and now via Python. Only, recently I haven't had the time to dive into it. Hoping to do a little research of how that works, over the summer.

    My approach is very similar to yours ... place the x,y,z values in a txt file, precede it with the appropriate rhino commands and load it up. You can read upon it in help, look up for Rhino script files.
     
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  11. ldigas
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    ldigas Senior Member

    It has always been my view that the waterlines, buttocks and diagonals, to mention just some, must be equally fair along with the sections to call the hull fair. Making it fair in one projection only means it is fair in none.
    Of course, there is always a chance that I misunderstood your meaning, and now look just plain silly ...

    p.s. Is there a way when writing these posts to have a keyboard shortcut for quote, bold, ... and on ... these commands on top?
     
  12. DCockey
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    DCockey Senior Member

    My experience has been that it's quicker to import the points into Rhino as a .csv or .txt file and then sort them manually by selecting and moving to the appropriate layer. The sort usually takes only a few minutes, quicker than it would take to create a script.
     
  13. DCockey
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    DCockey Senior Member

    Not contradictory as you explained. For example fairing for a build of a tightly controlled racing sailboat will generally take considerably more time than for a welded metal tug.

    There is also a fifth possibility:
    e) the surface is fair but lies further from the offsets than necessary to achieve the same degree of fairness. If this is acceptable surface modeling can go faster.
     
  14. CWTeebs
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    CWTeebs AnomalyGenerator

    And

    These guys are brilliant, and I think it's terminal.
     

  15. DavidJ
    Joined: Jun 2004
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    DavidJ Senior Member

    yes ldigas I agree about all lines needing to be fair and the resulting surfaces need to correspond to all of the lines in each view. What I meant was that with very simple hulls you only need to model one set of lines and the rest work out automatically. When talking about how long it takes to model a hull those are therefore the quickest type to model. Imagine something like a box shaped barge. The waterlines are perfectly straight between sections so if you loft between two sections you get a hull with no fairing necessary that automatically matches the waterlines. Many coastal ferries or small river ferries out here have hulls with simple straight sections that can be modeled like that. Also no matter how tough the rest of a hull to model a parallel midbody is also that simple. So again I was just referring to the original point about how long does it take to model a hull and at the same time agreeing with Mr.Cockey's point about how it depends on the shape of the hull.
     
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