# Maxsurf Problem

Discussion in 'Software' started by duraeps, Dec 22, 2008.

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### duraepsNew Member

hi, i'm a new user to maxsurf software.

currently i'm trying to use as many control point as possible to build up a 99% accurate ship referring to lines plan.

but as i can get the accurate waterlines, buttock, frames lines, the surface fairing problem arise.

how am i possibly fair the surface with tonnes of control points?

any tips or guidance can be given.

ur help is much appreciated~~~

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### pavel915Senior Member

If there is a lot of control points; difficulties will must arise in editing the surface. But the thing you can do is - be carefull when you are making the model.
In this kind of case, the thing i do is: i import the lines in rhino and make a smooth surface in rhino and then import it to MAXSURF, and if there are a lot to stations and water lines are to handle in the modelling of hull the main thing becomes the fairness of the curves.
If the cuves are fair and acurate then surface will be fair and if the curves ar not fair surface will be rough.
YOu can analyze the roughness of the curve by the command: CurvatureGraph

If you see by the command "CurvatureGraph" that the curves ar not fair you can not expect a fair surface- so you can then edit the curves first and if editing of the curve is not possible delete the curves who are not fair; Here you have to make a good compromise between "smoothness" and "acurity".

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### marshmatSenior Member

Hi duraeps,

As Pavel has pointed out, your fairing problem is likely the result of using too many control points.

Given a curve with three points, it's virtually guaranteed to be fair no matter what you do. Use five points for the same curve and it's pretty easy to fair it. But if you start using 10, 15, maybe 20 (I've even seen 50+) points for one curve, it will pretty much always have problems.

Think of control points as being a little like the ducks (weights) holding a spline batten. When the lines were penned by hand, probably only a handful of ducks were used for any given curve. By skillful movement of the ducks, a fair curve is created. You recreate that curve in CAD not by using more points, but by judiciously manipulating a small number of points to get the same effect that the small number of ducks had on the original spline batten.

4. ### Guest62110524Previous Member

when you loft a shapely yacht full size youi need tapered battens to do the body plan, and battens of varying stiffness for sheer, butts , wls and so on
can you vary the STIFFNESS IN CAD?

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### duraepsNew Member

Re: Pavel915

thanks 4 ur suggestion.

Ever thinking of using Rhino, but Maxsurf have taken most of my time.

Will give it a try~thanks!

Re: marshmat

Very imaginative~
i can imagine the ducks with skillful movement~ ;-)

Recreate curve in CAD~hmmn, that means i can use the point directly from CAD for a fair surface, rite?
so least point will be needed to create a fair surface.( i think )

still~~~ sound abstract to me.

should try that one also~thanks!

Re:whoosh

Nopă€‚ i dunno how to vary stiffness in CAD.

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### marshmatSenior Member

Most good NURBS-based modellers have the ability to manipulate knot vectors and point weights, giving something roughly analogous to "stiffness" of a batten.

It is generally not advisable to manipulate point weights to get the shape you want; that is better accomplished by moving points around and adding/removing rows and columns. Manipulating weights is usually done only at the very end of the process, to achieve small, local effects; it is very hard to fair a surface with varying weights.

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### Andrew MasonSenior Member

Try reducing the number of control points as much as possible and keeping the spline stiffness as high as possible, you may be surprised by how easily the surface fits your offset points. Adding control points and making the surface more flexible almost always makes things worse.

Also be aware that offsets almost always have some degree of error or noise in them, if you try to fit the points exactly you will get an unfair hull that is not a good representation of the actual hull shape.

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### duraepsNew Member

Thanks Andrew~

Ur tips really hit the point!

i follow ur advice and i manage to get a fair surface eventually.
thought not 100% to the original lines plan, still have 98% in similarity.

thanks to all those who lend a hand when i'm helpless. thanks!!!

p/s: still seeking a faster way to complete a hull~ ;-P ganbadei to all

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### iparpuraNew Member

First of all question is are parent lines from which you start faired well, if they are not and you have try to interpolate hull trough them your hull also will be bad faired. For well faired hull in most of the cases it is better for lofting not to use orthogonal sections like frames and waterlines . What curves to use depending of type of hull you want to generate. Ratios, coefficients and parameters you need from naval architecture part of problem take out from generated hull with non-dimesional section area curve .

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### alidesignerSenior Member

As well as setting the curve stiffness you can also set the individual control point weighting in Maxsurf. Just double click the control point and its the last setting. Surface must be NURBS for this to work.

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### Andrew MasonSenior Member

Please don't do this, its a good way to mess your design up even further. Weights are good for creating true circular or elliptical arcs for bilge radii, bow cones, prop shafts etc. but in my personal opinion it is not a good idea to use them for hull shaping or fairing purposes. It may be reasonable to use them to intentionally create an area of local unfairness such as a knuckle or bump, but as a fairing tool I would recommend against their use.

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### zeronameNaval Architect

hy..
Q to andrew
i saw some video in www.formsys.com on maxsurf v14 .
when it will be possible to get the demo or academic version of maxsurf 14.

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