Hull fairing

Hello

Thank you for a great forum!

I'm new to this forum and new to designing/drawing boats, but I have in my earlier days been building sailboats.

I have fore some years been schwanger with a trimaran I want to build, and I did for many years ago draw up the hull in Autocad. I drew it in 3d by keying in the numbers from my main hull offset table, that I made in a excel spreadsheet.

I then made a scale model in 1:100 from balsa-wood and paper-skin. What I discovered was that the hull is not 100% fair along the chines. So I've been thinking if there may be a program that I can import the model in(either as dxf or iges) where I can do the fairing, and I also want to flatten some panels on the hull for CNC-cutting? I then want to take the model into SW to do the bulkheads and interior, all ready for CNC-cutting.

So my question is what program would be suitable for this, and without draining my wallet completely?

Regards
Terje

 

I think you can do anything you want in AutoCAD, working in 3D and taking real measurements, using the multiple tools of AutoCAD.

 

Hello

Yes i probably could, but I was more thinking of a program that was not so much labor intensive and that had a nice algorithm for faring, and aimed towards boat-building, not general buildings.

Also I don't think Autocad has any function for making flat panels out of curved chines/panels?

Terje

 

You could do it the old fashioned way for a very small price...... Paper, pencil, splines and some duck weights.

I doubt that a one hundredth scale model will deliver sufficiently reliable information unless the full sized boat is to be a large one.

 

You could try Rhino - www.rhino3D.com


This will import your Acad drawings and allow you to create NURB surfaces. It will also flatten developable surfaces. These can then be re-exported as dwg or dxf in various Acad versions with quite a lot of control. You might have to play with export settings for truly optimal results. It will also clearly show which parts are not fair, and need changing. There are some issues about fairing with NURB surfaces which you can google, but in general they are fine for real world lofting.

The trial version I believe allows 30 days use.

 

Yes, I've been thinking about Rhino, but unsure if I can do that without special plugins?

How steep a learning curve is there, say compered to SW?

Terje

 

temo, if I were you would not begin now to learn a new program to do something you can do with AutoCAD.
Fairing of shapes can be done with AutoCAD, Rhino can not.
You can, after obtaining sufficiently good shapes, create a 3d model with AutoCAD and export it in igs format into Maxsurf, which has a module for development of plates very good.
Even if you know the traditional methods of developing plates, you could do it yourself in AutoCAD. Take my advice, try with AutoCAD, the forms are very simple and could develop with relative ease.

 

OK, so seems I have to dig into Autocad a bit before starting to look elsewhere. Any special functions you can mention, that will get me going.

I think I drew this up in Autocad R14 in 1997 so I guess if I look into today's version it will have some more option?

Yes I know they are simple shape plates, I can easily calculate them in the wurst case.

Terje

 

I seem to remember that, from the AutoCAD 2010 version, new commands / tools for working with surfaces were incorporated, that will go perfectly for surfaces that you're looking for. See attached picture.

 

Wow, I see.

This look interesting and all new to me.
Why fix something if it isn't broken!

Thank you!

 

It might depend if you drew it in LT or the full version of Acad? I'd hazard that Rhino would be a cheaper option over an Acad full version upgrade?

I'd also think that by putting a few diagonals, maybe waterlines too, through the created surfaces you could very easily correct any discrepancies. Easily done by intersecting surfaces in Rhino btw ie Curve(s) from Intersection. There is also a free add on available from a member of this forum in the software section which will add useful functionality to the basic hydrostats available in the program. Rhino was designed to be easy for Acad users to learn, so you should feel comfortable pretty quickly. It is not a parametric modeller but you can use the history function to good effect for lofting surfaces ie changing the curves and auto regenerate. So different to SW or other high end modellers, it (Rhino) is still a SW Gold Partner and the surfaces can be parametrically imported into SW.

Although pretty much anything can be drawn in 2D, I've found it is much faster to go through the options in 3D to optimise a fair shape. I've found the developed shapes in Rhino to be sound although with a more compliant material like plywood, compare to steel, you can get more curvature than the program 'thinks' - at least in the real world. There are very good tools for curve and surface editing - the simpler the surface in general the more fair.

I'm sure both programs (and others) can deliver the result you are after, so your decision. I've had hull(s) cut direct from Rhino Iges files as well as a stack of 3D printed items and some injection mould tools. My gut feel would be use Rhino to fair the surfaces and export into SW to do the rest of the work. I've not used Acad to export to SW and remain a parametric surface import in the operation tree, so cannot judge how good it is at that.

 

You can download most Autodesk products free on a 3 year student licence:
http://www.autodesk.com/education/free-software/all
Not for commercial use, but fully operational.

 

From your first post it would seem that you have Solidworks available so why not just use that for the whole of the design work rather than acquiring additional software and learning to use it? I have found SW adequate for drawing typical boat hulls, although it may not have the range of surface functions that some of the alternatives offer, at least not without buying 'plugins'. I have used the standard 'loft' functions in SW to generate hull shapes and I have flattened developable panels using the functions under the sheet metal menu. This flattening does have some limitations, I think that at least one side of any panel to be flattened needs to be a straight line before flattening, but I have found that possible for the hull shapes I have so far worked with. If this is a problem, one possibility might be to find a straight line on the panel that an be used to divide the panel into two pieces each of which have the cut edge as a straight line.

 

It is not always about what software you are using and the tool set that is available for fairing and surface generation, but more helps. Sometimes its the methods and techniques being used can cause the problems. In the files you posted you seem to have used polylines instead of curves for the chine lines. This makes it impossible to fair the most important lines for the construction of the surfaces in your design. Rather than trying to recreate the processes of the drawing board with lines for all sections think about stepping back in time a little further to when half models were made and all the lines were taken from them. That way you only need a few target points, say bow, stern and say three sections, then you only have to pass a curve through these points, then fairing the curve becomes simpler, construct your surfaces from these curves, then you can get your lines from the model you have created.
I used this method to create what is in the pic. I put the curves through a few of the sections plus bow and stern, I then faired up the curves a bit more then did the surfaces. You can see in the bow area the difference in the chine lines.

 

I agree with the use of splines is more appropriate than using polylines. However, in my opinion, not only about getting smooth curves, but curves pass exactly the cross sections he has defined. Use only a few points occur, of course, smoother lines but will not guarantee that the lines go through all the points, which is what, I guess, he is trying to achieve. What he should do is to draw splines passing through all desired points and go slightly changing the position of any of them (ie, the shape of each frame) until the curves are adequate.