Maxsurf or Rhino for twin-keel design?

[BillyDoc]

Hi Everyone,

I’m interested in designing and building a twin-keel yacht out of aluminum and am looking for software to use, preferably comprised of a suite from the same manufacturer so that the files are actually compatible. I already have Mechanical Desktop (version 4) and Rhino (version 3) and am trying to decide whether to elaborate the Rhino with RhinoMarine, etc., or to jump into Maxsurf and their add-on modules. I WILL be tank-testing the design, but I sure would like to minimize the model making if possible.

So, which software route would be the best? Will either package calculate meaningful variables from asymmetric airfoils mounted off-center? Or, am I basically on my own with this one and doing the keels separately from the hull — using the tank?

Or should I be looking at some other package?

Any guidance will definitely be appreciated!

Bill Cushman

[Tim B]

You should certainly build the foils as seperate surfaces to the hull. Sounds like you have a bit of experience so the hydrostatics shouldn't be too much hassle to do by hand (for fixed trim). Personally, I find Rhino much easier to use than Maxsurf, and as you've got a copy, I'd suggest you use it. MaxSurf might do some things more easily than Rhino, but there's got to be a damn good justification for spending a lot more money.

If you want to know more about stability methods, drop me an E-mail.

Good luck,

Tim B.

[BillyDoc]

Thanks for the reply!

I rather thought I would be on my own on that one, and you are right, I can always do the hydrostatics by hand. Although, being of a lazy nature, I’m always looking for an easy out and getting all the data absent the keels is a fine head start.

And the design area I am really concerned about is not hydrostatics, but hydrodynamics. Which is an area that I understand you are working on. And thank you for that! It would be so nice to be able to design a hull on my trusty computer, check out the hydrostatics as I go along (in real time of course, since I’m dreaming now) with another window open showing the behavior of the water as it flows past the hull/keels with a series of little colored vectors. Oh, with a nice display of all the cumulative force vectors acting on the hull as well. And the sails. And everything parametric with a built-in optimizer too.

*Sigh*

As it now stands I will be building models and testing them. I do have access to a CNC milling machine, so if I can get my hull specified and the file transferred to Mechanical Desktop I can generate a tool path and cut the model pretty accurately. So far, my MD doesn’t get along well with Rhino output files, although sometimes they work if I go via ACIS. IGES is a complete bust.

I plan on building a small test apparatus by placing a trolling motor in the bottom of a “tank” that is something like the drawing below, with various arrangements for measuring the forces involved. (All based on supple fishing line, various pulleys, and a balance.) Wet work, for sure. The part where the model floats will be glass, and I hope to learn something about the hydrodynamics by trailing a colored thread past the hull at various locations.

[marshmat]

Oh, to have software that could do that... (or hardware that could do that...)

Real-time hydrodynamics computations are simply not possible with the average desktop computer. Getting all the drag coefficients, force vectors, etc. takes hundreds of iterations of the calculation; the dual-processor IBM we use to run that stuff on the solar cars typically takes all night to analyze a six-metre car, and that's just in air- no fluid interfaces. And the software is bloody finicky, too- usually takes hours to set up a run and get it working, and then you have to check it at 11 pm in case it messes up and starts running to infinity.

Since you already have Rhino (and it's fun, easy and powerful) I'd stick with that. Not worth spending more money on completely new software when you already have a lot of what you need. Speaking of which, anyone have any experience with the Rhino marine plugins, how useful/accurate they are?