Problem with splitting a lofted surface


I have two lofted surfaces (option loose). The upper surface with the green loft curve is resulting in a surface that can not be splitted by the cutting plane. The lower surface with the cyan loft curve is resulting in a surface that can be splitted. I can not find out what is wrong with the green problem curve. Can you help me?

See attached rhino file.

Problem with split of a lofted surface.3dm (396.2 KB)


Hi Bas,

 I thought I recognized that hull form. You did the lofting tutorial a few years ago with the RhinoNL group right? 

 I haven't downloaded your attachment and taken a look yet but my first guess (before making some coffee and looking at your lofts) is that there may be some co-incident points. I've been given Maxsurf generated hulls that wouldn't split that had chines and greases formed by stacking control points. Just a guess and I will take a closer look.

Hi Bas - the stern splits but the long curve of intersection with the plane comes up a little short at the bow end. I ExtendSrf-ed the front vertical edge of the surface by 100 to give a little more overlap with the plane, then it works OK.


Hi Joseph,

This hull is made by a student at the technical university of Delft. I am teaching them hull form generation with Rhino. The method is indeed the same as published by Hope you can help after your coffee, :slight_smile:


Hi Pascal,

Thanks, I did that test too. Extend surface is too much a trick which I can not teach to my students. I would like to know why one curve fails while the other doesn’t.

Hi Bas - I can’t tell you why in any detail, myself… it looks to me like it is a weakness in the surface-surface intersector that appears to be fixed in V6 - the Split works there. The Intersection curve in V5 ends on a knotline, V6 takes the curve to the edge as expected…


Hi Pascal,

This is good news. Does that mean that this split will work in Grasshopper V6 (within Rhino V6) ?

Hi Bas - yep, that seems to work:


Great, good to see that Rhino V6 is getting better.

This method does not work for Smart 3D.

Dear Michael Martinez, what do you mean with this method? Cheers, Bas

Hi Bas, I just mean the lofting method that you speak of. The trimming of the surface isn’t accepted by Smart 3D. Just been looking for a way to make this hull that I’ve been working on.

Hi Michael, there are a few tricks that might help. Can you share your model? Did you try _ShrinkTrimmedSrf?
Cheers Bas