Displacement software

Discussion in 'Software' started by gonzo, Oct 25, 2009.

  1. gonzo
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    gonzo Senior Member

    I am still drawing with a pencil, but the displacement calculations are just tedious work. Is there softwere where I can input the offsets and then the weight of building materials and will give me the waterline? Then I could change things like engines or tanks and it recalculates the waterline?
    Thanks
     
  2. apex1

    apex1 Guest

  3. gonzo
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    gonzo Senior Member

    I wonder if there is software where I can drag and click elements on the design and it will recalculate CG, waterline, etc.
     
  4. apex1

    apex1 Guest

    Within some limits, Delftship and Freeship+ (basically the same) do that.
    And they are quite easy to handle and have not a steep learning curve.
     
  5. gonzo
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    gonzo Senior Member

    Can you, for example, shift engines fore and aft?
     
  6. Guest625101138

    Guest625101138 Previous Member

    Yes. Use different layers to specify the envelope or as much detail as you like of any parts and move them around as you like.

    Delftship has some limitations compared with Freeship. Delftship pro has a bit more functionality.

    Rick W
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    gonzo
    You need a set of hydrostatics to do this quickly and properly. Once you ahve a set of hydro's for your hull, you know where the KB and LCB etc are, then all you need to establish is the distance from the LCB to the LCG, you have a lever, then you ahve the displacement, then look at the hydro's for the MCT 1cm...and so on.

    One doesn't need to play with layers, as suggested above, that just implies ignorance of how to design.
     
  8. gonzo
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    gonzo Senior Member

    Ad Hoc: That is how I do it by hand. It is tedious, slow work. I want to click and drag. Can you enlighten us out of our ignorance?
     
  9. Martijn_vE
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    Martijn_vE Marine software developer

    Not neccessarily true at all. What Rick refers to is to represent weights in different layers of the model. By changing the geometry, the weight and corresponding center of gravity are updated by the software, very similar to using Excel only fully automatic.

    Using Excel in different design stages is very common, no matter the size of the ship. Why would that imply "ignorance of how to design"?
     
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  10. gonzo
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    gonzo Senior Member

    I suppose that my elementary knowledge of Excel is not enough. Back to the classroom
     
  11. Guest625101138

    Guest625101138 Previous Member

    Gonzo
    Martijn is not saying you should use Excel he is simply pointing out that Delftship can be used to list the boat components as you would with a spreadsheet.

    The benefit of using Delftship is that you can move things about as you like and not only automatically get updated CofG but can quickly see the result relative to the rest of the boat.

    The simple example of my V11J pedal boat attached shows the result of using the layer control to remove the gearbox from the image or move it to a different location. This took all of 20 seconds. The boat CofG is automatically updated based on the weight data I have entered for the gearbox.

    Layers are commonly used in CAD programs to reduce the complexity of what is being worked on at different times.

    Delftship is the easiest drafting (or rendering) package I have used. Once you get familiar with "surfaces" it is very easy to use and quite fast. I have sent output files from Delftship to milling shops for machining metal parts and routing foam plugs.

    Rick W
     

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  12. Ad Hoc
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    Ad Hoc Naval Architect

    Gonzo
    As i said, if you can get a set of hydrostatics for the hull, then i can help. But that doesn't help you, since you want the hydro's in the first place! A quick method, draw the body plan on a set of graph paper. For 10 stations, measure, roughly, using the graph paper, the area. Then Simpsonise them to get the basics hydro's.

    Martijn
    "..By changing the geometry, the weight and corresponding center of gravity are updated by the software,...Why would that imply "ignorance of how to design"?.."
    This is because all one is doing, by this method, is trial and error, not design. One just "plays" about until the desired result is obtained. Anyone can do that with enough knowledge of using the software, but it ain't design.

    With a set of hydrostatics, with the current GA and layout, the weights and centres will have been done. If the trim is wrong, after plugging through the hydro's, then all one is looking for, is the total tonne.metre moment.

    If the total tm is say 100, then this means moving, for example 10tonne 10m, can this be done in the design?...if the total displacement is say 25tonne and the boat is say 20m with an engine say 5tonne, then clearly no, since this would mean moving the engine 20m. As a crude example. One doesn't need to "play" to design, one needs to understand what 'design' is!
     
  13. peterAustralia
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    peterAustralia Senior Member

    HULLFORM works exactly the way you describe

    You enter a table of offsets and away you go.
    Actually it is not quite that simple, but is fairly close.

    You start by making a new design, you have to enter the number of lines.
    Example a V hulled ama would be the most simple and have 2 lines.
    A flat bottomed sharpy would have 3 lines.
    You enter draught, stem height, transom height, overall width and overall beam and then go

    It will make a shape that looks weird, do not panic, add some more sections and then slowly but surely you add data points. As to displacement calcs, what you do is enter a figure along with the center of gravity and it shows draught, freeboard and trim angle. You can keep on increasing displacement until gunnel touches the waterline if you really want to.

    There are a couple little tricks, if you have a kink in the lines, it is smart to have 2 sections say 10mm apart, the line between these 2 sections has a very high intersection flexibiity. This separates the line into 2 parts, very useful if you want to change something after you have added the offsets.

    IF You are going the method of offsets, HULLFORM is excellent.

    Example, say I had the dory book by John Gardener (I do in fact), and wanted to put a dory design into the computer. First I would convert all to metric (take a while, but I only use metric) and then enter the numbers into the computer. For a complicated thing like a swampscott dory I could do the entire process in an hour, and have it perfect.

    If you have problems and cant get it to do something, ask,,,,, if you ask you can get help..

    you can ask me if you like peterevans_33 at yahoo dot com dot au

    HULLFORM is free.

    If you have something simple, show me and maybe I can make a start for you. I have a little spare time until I start my new fulltime job in a few days.

    Once again,, if you are going down the offset path, Hullform is excellent. If you are drawing freehand, and want to bend curves etc, maybe another software package is superior. I am sure freeship, hulls and delfship and superior products, but for just doing offset work, hullform is excellent.

    If you have a diagram, and a smallish table of offsets, email them to me, and I can email back a hullform file, from that starting point you can modify this line, modify that line, move this station etc etc , and see what happens.

    kind regards
    N Peter Evans

    peterevans_33 at yahoo dot com dot au
     
  14. Martijn_vE
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    Martijn_vE Marine software developer

    Really?
    You seem to keep missing the point here.
    Rick is referring to a method where the software calculates the cog of a set of weights while adjusting the location of individual weights graphically.
    Yes, that's design.

    On the other hand, how to calculate the trim angle from the calculated cog and cob is not design. That's hydrostatics.

    But I think we're getting off topic here.
     

  15. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Martijn

    Clearly your definition of design is totally different to mine.

    I'm referring to something that is real, and has real attributes and can be verified by other independent sources and can be built. Something that has been created from nothing from many sources to arrive at a solution.
    You're referring to how a software can be used to move things quickly and having all the 'numbers' crunched for you. But of course without any verification, since the computer doesn't know what is right or wrong.

    ..and never the twain shall meet.
     
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