Modeling boats in Freeship-The techniques of Using the sofware

Discussion in 'Software' started by lewisboats, Nov 1, 2009.

  1. Guest625101138

    Guest625101138 Previous Member

    The greatest revelation in using the tool is to understand what the mouse does. Play around with it and get used to it.

    Right mouse button held down allows you to move the object using the mouse.

    Mouse scroll allows you to zoom in and out.

    Right click brings up a menu that allows you to do a few intersting things.

    Rick W
     
  2. capt vimes
    Joined: Apr 2009
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    Location: Austria

    capt vimes Senior Member

    question about GZ curve computation

    i just recently downloaded Free!Ship 3.1+ and played around a little bit with it...

    i would like to know if this automated GZ curve calculation which comes with the version is to be trusted in a way... :confused:

    i get some very strange curves for the modell attached and i do not think that at a VCG of 1.3 m from the bottom of the hull this crap still has an AVS of >160°... (see screenshot...)
    i just cannot believe that...
    ok - the freeboard is excessive, the sheerline negative and that is all done by intention because i wanted to draw something save and roomy without this nasty topsides you see on all the smaller boats....
    you will find the relevant figures of this modell in the attached hydrostatistics file...

    this was the outcome after some hours of cursing and swearing... :p
    if you wish i could attach the .fpm file as well....
     

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  3. Martijn_vE
    Joined: Apr 2005
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    Location: Netherlands

    Martijn_vE Marine software developer

    Just post the .fbm file and I'll see ahat DELFTship comes up with. Free!ship 2.6 was able to calculate crosscurves, which can be used to calculate the righting levers. However the calculation of cross curves in version 2.6 ignores the change in trim, which can be considerable for boats like these. I doubt that Victor has modified it, which makes it pretty much to useless. If you can specify the weight and center of gravity I can easily verify the curve of stability for you. I will need the .fbm file in version 2.6 though.
     
  4. capt vimes
    Joined: Apr 2009
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    Location: Austria

    capt vimes Senior Member

    the version i made this was 3.1+ and i cannot open it with freeship 2.6...
    so it might be that you are also not able to import it to delftship...
    should i export it to offsets?

    nevertheless... here are the files...
    and thank's! ;)

    btw: i used lackenby to increase the CP to 0.52 which 'distorted' the hull somewhat... looks like a powerboat now... :p :D
    designweight is somewhere between 7.5 and 8 t...
    but to define the CG now correctly... sorry - cannot do that because i was just playing around a little bit and did not start with number crunching... probably somewhere around the LCB and 1-1.3 m above the hull bottom... probably :confused: :D

    oh - another thing... what is meant with 'trim' in this connection?
     

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  5. Martijn_vE
    Joined: Apr 2005
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    Location: Netherlands

    Martijn_vE Marine software developer

    Can you export a FEF file or to a .Part file?
    These are the formats I can import into delftship.
     
  6. capt vimes
    Joined: Apr 2009
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    Location: Austria

    capt vimes Senior Member

    here they are... and thank's! ;)
    the .fef file gives me an error when trying to upload it...
     

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  7. capt vimes
    Joined: Apr 2009
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    capt vimes Senior Member

    just press the right mouse button, hold it and move the drawing by dragging it with the mouse... the pointer actually becomes a small hand if the right mouse button keeps pressed....

    for that i think you have to play around with the controlpoints...
    at least i know of no way to actually give the program the info for a particular radius...
     
  8. Martijn_vE
    Joined: Apr 2005
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    Location: Netherlands

    Martijn_vE Marine software developer

    Well I managed to import the part file.
    First thing I had to do was move the model up so the bottom of the keel coincides with the baseplane z=0.0.

    I then calculated the curve of righting levers, assuming the VCG was located 1.30 m. above the bottom of your canoe hull, or 3.33m above the bottom of your keel.
    See the attached PDF for the results.
    The results are disappointing, probably because your VCG is set so high.
    A good value to start with is to assume it's located 0.10 m above the wl plane.
    The draft at 7.5 tonnes is 2.40m, so I put VCG at 2.50 and calculated the stability again. This time values are more realistic, with a range of positive stability of almost 130 degrees.

    If you want to go to see with this yacht I'd recommend more stability.
     

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  9. capt vimes
    Joined: Apr 2009
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    capt vimes Senior Member

    thank you very much martijn - i really appreciate your help and advice!

    i figured out that i gave the wrong VCG yesterday as well after going through the hydrostatistics table... although the drawings have set their 0 level at the bottom of the canoe body - the hydros asume the baseline at the bottom of the keel...

    this was and is actually no real yacht-designing-project of mine... ;)
    i just downloaded the software on friday and kept playing around with it to see what might be able to be done with it and what not...

    i leave the designing/number crunching with the professionals because those are the ones to whom all the respective ratios have a meaning and who are educated and experienced enough to build a boat which does float AND sail well...
    i would be very fortunate if my own designs are floating upright only... not to talk about their sailing characteristics.... :rolleyes: ;)

    another question:
    what does this 'trim' stands for, what does it mean?
    Trim -0.057 (m)
     
  10. Martijn_vE
    Joined: Apr 2005
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    Martijn_vE Marine software developer

    It simply means that the drat at the stern is 0.057 more than the draft at the bow.
     
  11. magwas
    Joined: Oct 2009
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    Location: Hungary

    magwas Senior Member

    How to assure that hidrostatic calculations will be correct

    This is what I have learned from my own errors. Please those who have more knowledge of the program, check this.
    Hidrostatic calculations can lead to strange results if there are problems in the model.
    The problems can be pinpointed with tools/check model.
    The most common problem is leak points. Leak points are green in wireframe view. These can be there for a multitude of reasons:

    - the top of the boat is not closed.
    It is not a problem actually. The problemtic leak points are those below waterline. If you want to see the "check ok" message however, create a new layer, select the leak points, and add a new face. It is like you have put a canvas to your boat against the rain. Now hide the layer, and do not assign specific weight to it. Whenever you check the model, check on "Use for hidrostatic". If you don't see OK, you will know that there is a problem to be addressed. Before you actually do hidrostatic computations, just check "Use for hidrostatic" off.

    - a non-hidrostatic layer in the shell.
    All the outer surface of the ship should be in a layer which is used for hidrostatic, and all the other surface should be non-hidrostatic. It might mean that you should split a layer to two. In my last design there is a single panel, which is partly above the cockpit deck, being part of the outer surface. Its below-deck part supports the cockpit, so non-hidrostatic. It is a single part, but it should have been modelled by two faces in two different layers.

    - a hidrostatic layer within the boat
    It seems odd, but you should not use layers within the boat for hidrostatic, see above.
    If you model frames, bulkheads and such, you will not be able to calculate with their mass. I think it is not a major problem with a yacht, but I don't know what would I do with a bulk carrier.

    - double point or edge
    It is the trickiest part. There are cases when two points are at the same position or very close to each other. It is not always problem: you can get rid of triple edges by introducing double points (see below). The main point is to not have faces in a hidrostatic layer connected to different points in the same position. If you keep only the surface layers turned on when editing surface, this problem should not happen. To check for duplicates, you should select the suspect point, and set one of its coordinates off. It will move away, and you will see if there is another point in the same coordinates. If not, just undo the move (edit/undo). If yes, the easiest thing is to delete the point and recreate the faces which went with it on the duplicate which is not moved.
    Be careful, because you might destroy reference points which is needed: if there is a point, which is connected only to faces which is connected to the point which will be deleted, it will be gone. You might want to create the new faces before nuking the moved duplicate point.
    You may want to use a point in a non-hidrostatic layer to create a face in a hidrostatic layer. If the layers have overlapping points at other places, you can select the point in the non-hidrostatic layer, and hide it to avoid picking up wrong point.

    - triple edge
    Triple edge is an edge which is connected to more than two faces. It is green in wireframe view mode. This can create nasty things (access violation) in the working of the program. The best way to get rid of triple edges is to export some of it to a part, undo to the creation of the triple edge, and import the part.
    YOU WANT TO EXPORT/IMPORT only INTERIOR PARTS! The export-import trick disconnects the surfaces, introducing leak points in hidrostatic layers because double points will be created.

    I hope this helps.
     
  12. magwas
    Joined: Oct 2009
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    Location: Hungary

    magwas Senior Member

    Design for plywood and steel origami

    Plywood needs strakes which bend only in one direction. Origami steel boats and tortured plywood need also this, but to a lesser extent.
    Unfortunately the models created by file/new not such ones.
    However Carlson's hull software is for developing such hulls. There are also a lot of .hul files coming with it. Unfortunately hull.exe is very badly written. I use linux, and it is not forgiving with bad software. If I am lucky, I can modify a few points in a design before hull.exe dies, and if I am extremely lucky, I can even save it.
    But Freeship can import these hulls, and if you set view mode to developability check, you will see whether a part is developable. The red parts are the problematic ones. Do not panic if the chines are red, it is no problem. Red generally means: "Use your brain and double check whether there are problems with the way it bends."

    When the design is ready, you can export to part, delete and re-import chine by chine if you prefer sharp, well defined edges. Beware that you won't be able to do any hidrostatic calculations after that, but developability check won't show you the red in the chines. There is a little difference between chines developed this way and without export-reimport, but I think it worth it only in extreme cases (very narrow part connected to a wide one in a large angle).

    I used to use tools/develop to develop the plates (also bulkheads and such), and export to dxf from there.

    I use a 2d CAD program (qcad) to arrange the plans for printing.
    With origami boats, you can move one point of adjacent strakes to overlap, measure the angle between the two to-be overlapped edges, and rotate around the overlapped point to get it right. As the edges are not lines (but splines I think), you should first draw lines between the control points (at least in qcad).
     
  13. Victor T
    Joined: Feb 2007
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    Location: Ukraine

    Victor T Senior Member

    You have committed one error - have not paid attention for the line below.

    NOTE 1: Draft (and all other vertical heights) is measured above the lowest point of the hull! (Z= -2.000)

    You set estimated Z CoG = 1.3m, but it must set as 3.3m

    But is better it is necessary to make here so
     

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  14. capt vimes
    Joined: Apr 2009
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    Location: Austria

    capt vimes Senior Member

    thank's victor

    i realized the mistake the same day... even before martijn told me so...
    to place a weight in the ship for compensation is a good idea... but who if not you is the one who knows how to get the best results with his software... eh? ;)
     

  15. Victor T
    Joined: Feb 2007
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    Victor T Senior Member

    About this method (idea) you can see in "FREE!ship demo 3+deck+gruz_man.fbm" from v2.94 of Freeship Plus. Same users this way for stability calculation use more then one year. See hystory:


    Test only Version 2.91+
    Released March 31, 2008
    New features:
    * Added GZ curve calcs for imported from hydrostatics calculation displacement D and CoG Z


    Test only Version 2.92+
    Released April 10, 2008
    New features:
    * Added calculation and input some data for ship sinkage (see sample in FREE!ship demo 3+deck+gruz_man.fbm )

    Regards.

    Happy New Year 2010!
     
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