Ships Curves in AutoCAD

[g-ship]

Does anyone have a source for actual ship curves based in AutoCAD?

[jehardiman]

Autocad cannot do ship's curves. The way curves are formed in autocad cannot handle the proper curve form of ship's curves

[CGN]

You can try looking for some pictures of the ship curves and scan these in
AutoCAD.., but why not use splines and the curves options on AutoCAD?, Alias has some kind of electronic "French Curves set", this tool is on alias and studio tools, but I have no experience with them or how the actually work.

http://www.alias.com/eng/about/resea...enchcurves.pdf

[stewi]

It is not impossible to create boat shapes with ACAD. However, these are just surflines and no bodies like in Solid Works.
Create 3 D lines for your (1/2) hull shape. Use edgesurf and set the surftab to the desired number of sections. Mirror your half model.
http://img481.imageshack.us/img481/523/acad3wf.jpg

[jehardiman]

The question is not about wether you can make curves or hull forms with autocad, the question is wether you can accurately make ship's curves. It has been my experience that the answer is no. I have experienced several cases where other engineers have drawn in autocad one of my hull form L&O's done with splines and ship's curves. The structure was was lofted and built so they were able to use returned offsets. In trying to get pre-cut plates to lie against the skin, they were way off, sometimes on the order of an inch (25 mm) both in and out (too much or too little curvature). This is because the way autocad handles it's b-splines. A ship's curve has a continious change in the rate of curvature, whereas autocad uses an n dimensional b-spline which limits the developed curve sections to sectors of ellipses. Yes there is a NURBS function, but in order to curve fit with that in "real" applications you need to know so much more about the curve that you already can mathematically describe it better than the NURBS function.

It's the classic computer pixelation problem, in order to fit it into 0's and 1's you cannot get a continious function.

[g-ship]

I am just starting out in the boat design world and appreciate all the help I can get! I have used autocad in architecture for over 10 years and of course would like to bridge that experience and knowledge over to my interest in boat design. I am enrolled in the Macnaughton program and would like to do the drafting work in cad, thus the original post. Can some of the design process be done in cad and then imported to other programs for completion. If so, any suggestions on the best way to integrate?

[jehardiman]

Start with CAD, Stay with CAD. Then it is always "incorrect" in the same fashion. In my opinion, CAD only saves time if you're going to go straight to CNC cutting. Otherwise, I can sketch/draft a one-off piece faster by hand with enough detail to allow a machinist/shipfitter to make it up.

Remember... "paperless offices" arn't...

There is also some problems in moving meshes and solids between programs (i.e. Rhino to Acad and vice versa). And in how the programs handle local/global item axes, surface normals, and surface stiching.

[CGN]

Ok, is about Hull lines, yes you can use AutoCAD, almost any 2D CAD will do, but I think you should look for something like Rhino or Touchcad, if you are taking courses and really into the boat/design-building, try rhino or touchcad, you can use these to do almost any 3D shape or geometry that you want.


I use Prosurf, Freeship, to design the hull lines, then export to rhino to finalize the model (wheelhouse, gear, accessories on the hull), and I use a CAD software to "sketch" any ideas, elaborate general arrangements, structural dwgs, systems..etc., CAD is very important and very integrated in the design process and to do final drawings for design or construction.

an MCAD (Solidworks, PTC etc..) can be used to model the structure of the boat and hull accessories or gear, but is more production oriented, IMO.

Cheers!

[Gilbert]

Hi g-ship,
I have been designing boats in autocad since 1987 with lisp routines written for me by my mathemetician brother. That was BEFORE autocad had a spline function. It has been satisfactory but it is tedious. My suggestion to you is that you go download freeship software which is opensource and free. I can accomplish as much with it for a bent frame boat in an hour or so what would take me many hours in autocad. I still prefer the results I get with autocad lisp routines for developable hulls. Freeship at this point in it's development only tells you if your hull you've drawn is developable, it doesn't draw one for you that is developable or draw sections that would be developable. Freeships developer seems very agressive about making it better so I doubt if it will be long before it has most of what every desiner would like to have. You can even contribute if you are a programmer. www.freeship.org
Cheers,
Gilbert

[g-ship]

Ok, so if I'm hearing correctly, you advise canning the autocad in favor of one of the above. So what's your opinion on which one of these three programs offers the best overall experience for what I'll be doing in the Macnaughton course: Fastship, Freeship or Rhino? I have downloaded trial versions of fastship and rhino and the free version of freeship. I can get an educational version of Rhino through Macnaughton. Any opinions?

[CGN]

Rhino is best overall, but needs a plug in for hydrostatics.

Freeship best tool for Hull design only, (includes hydrostatics calculations).

You can use it to design your hull lines and then export to any CAD or a software like Rhino, it won't save NURB surfaces

FastShip similar to Freeship, and is able to write Rhino Files directly or save as a IGES (Nurbs).

Other good option is TouchCAD that can be used to model you hull and do all the rest inlcudes hydrostactics, plate development, and capable to model almost any shape or geometry.

like you see there is no perfect software but some of them can be used a full solution, even in most design offices there is a software specialized on hull design (ProSurF, FastShip, Maxsurf etc..) then this surfaces are exported to software like Rhino/Shipcam then to shipconstructor/MCAD...etc..and AutoCAD is behind producing final drawings, sketches or preliminary concepts that can be then model in any of the software's before mentioned

[g-ship]

CGN-Thanks for the advice. I'm thinking if I only want to learn 1-2 programs at this time, probably Rhino and Fastship. I'll work through the tutorials and see what I think after that. Would these two be too redundant?

thanks again for your time and expertise.

[CGN]

IMO, not at all, using a hull modeling software like FastShip (I use Freeship and Prosurf) is faster, lot's of ways to control surfaces, easy to fair a hull, and I can check real-time the intact stability as I progress with the preliminary design, once is done (hull lines) I export to rhino and finalize the rest of the model, superstructure, deck gear, accessories...etc..you should probably have a look at Maxsurf they have free version for students and I think the cost is lower than fastship.

Have a look at the file was model using freeship

good luck

[Raggi_Thor]

I agree with CGN and others. Try FreeShip to get used to this method for early design. Then use Rhino to make a detailed 3D surface model. Then use AutoCAD to make 2D working drawings with dimensions, text, frames and title blocks. You can quicly section your model in Rhino and export the curves to AutoCAD. IntelliCAD is a low cost AutoCAD clone.

MCAD?
Alibre design is a low cost alternative to Inventor and Solid Works. Rhino files can be inserted directly into Alibre as a surface feature, used to terminate extrusions for example.

[Raggi_Thor]

Forgot to mention, I also made my own spline functions in AutoLISP (AutoCAD) 15 years ago. I even made a routine for unfolding the strakes in lapstrake boats. Now all this and much, much more like curvature analysis, blending of surfaces with second or third grade continum is standard features of Rhino.