help with maxsurf

[snow 57]

can any one help me with maxsurf? I've been playing with it for a couple of months and have hit the wall. i'd just like to chat about some problems I'm haveing

[bhnautika]

Go for it, what's the problem

[snow 57]

I don't undestand how the program can read my design if all the surfaces are not bonded. I keep trying to bond the surfaces as I go and find it impossible. I also have trouble accurately connecting the surfaces if I don't bond them, I seem to be always going back and adding control points?

[Andrew Mason]

One of the first things to do is work out the topology of the surfaces you will be using. In some cases this is straightforward, for example a hard chine hull with a chine flat will be three surfaces running full length (topsides, chine flat and bottom) and bonded along common edges.

If you set up the surface topology and bond the edges early, Maxsurf will take care of the addition of control points across the bonded edges for you. If you try to design each surface independently, and then bond them together late in the design, you will invariably have problems with mismatching control points, surface stiffness etc.

The commonest problem with people learning to use Maxsurf is the use of too many control points and surfaces that are too flexible. Wherever possible try to get rid of control points and keep the surfaces as stiff as possible, it makes it a lot easier in the long run.

[snow 57]

Thanks Andrew,
I have been trying to keep the control points to minimum and my [catamaran] deck and hull join is fine outboard but when I try to make the chamfer pannel and bridge deck I start to loose control and and can't get the chamfer to run out to the bow while curving around to the front of the bridge. I try adding more controls but that ruins the fairness of my hull. Do I have to go back and refair the hull? Or do you think the chamfer should be another surface? I've done one with a separate surface but I am worried that when I come to do "Sea Keeper " if I don't have all the surfaces bonded it will affect the result.
I have just found this site so if my questions seem jumbled it is because I havn't been doing Maxsurf for a couple of weeks[ I got very frustrated with it] and I'm a bit too busy for the next week to really get into it, as soon as I do we can probably sort something out.
Once again thanks
Snow

[Andrew Mason]

Best thing to do is drop the upper edge of the inner topsides down and bond an extra surface as the tunnel fillet.

If you do something as a aseparate surface that is not bonded, it does raise the possibility that Seakeeper or Hydromax may not see it as a continuous hull envelope (although they are generally pretty good at sorting out ambiguities). In this case the alternative is to make sure the surfaces poke through one another adequately and then use the intesection as a trimming boundary. I don't know if you have played with the surface trimming in Maxsurf but it is fairly powerful.

The limitation with trimming is where two surfaces are tangent, in this case the intesection can become undefined as it may cease to be a single line (think of two parallel planes touching one another) so the surface/surface trimming can struggle in this case. In this situation bonded edges are preferable.

[snow 57]

Hi ,
Just a quick thankyou to Andrew for that bit of advice. I have been Maxsurfing today , tried the trimming you suggested and hey presto I have made some progress. Is there any limit on trimming? I mean the number of surfaces.
Snow:

[Andrew Mason]

I don't recall the limit on the number of surfaces that can intersect and trim, but it is reasonably high. The major limitation is likely to be the difficulty of visualising and managing large numbers of trimmed surfaces, this can get pretty tricky once surfaces start proliferating. Program performance can take a real hit as well so try not to over-use the trimming.

regards

Andrew