# Pleated Sweep2

Problem50.3dm (957.1 KB)
I am trying to build a hull form. Because NETWORKSRF will not allow me to use frames with crossing lines, I have to split things apart.

In the attached, I have the stem in which I have tried to build using a SWEEP2 to a point. I am curious why the surface comes out accordion pleated and how to correct.

Iâ€™m not sure it does what you want but networkSrf is happy to make a surface from these curves.

-Pascal

You should avoid making 3 sided sided surfaces. You are better off generating clean smooth 4 sided surfaces then trimming them back to 3.

Here is a ship hull tutorial https://www.youtube.com/watch?v=3XkdIsleAqY I think youâ€™ll find helpful.

Definitely stick to 4 sided surfaces as Jason said. It also looks like youâ€™re modelling just down to the waterline only, which will cause added complications in comparison to modelling the entire underwater shape.

Have a look at the attached file to see how a four sided surface would fit into this shape - I havenâ€™t managed to hit your existing curves within any acceptable tolerance but it should give you an idea. You could add in more control points if needed and start shuffling them around to get closer to your desired shape.

I would also consider rebuilding all the curves to make them simpler - the fewer points you have to edit the better!

Problem50.3dm (1.9 MB)

I would love to make them 4 sided but the data is waterlines and frames. I have to match the actual data as close as possible barring errors.

Copy of a description of my method for creating hull surfaces. While this description starts with a table of offsets it also applies if curves already exist. Just skip steps 1 through 4. One of the key elements to the method is extending curves past the edges of the hull to create rectangular topology.

1. Import the offsets into Rhino as 3D points.
1. Create a first set of curve (waterlines, buttocks, stations (frames), sheer, keel/rabbet, etc) through the 3D points. Check for obvious transcription errors. Examples include mixing up 1â€™s and 7â€™s, 3â€™s and 8â€™s, 2â€™ 11 3/8" instead of 1â€™ 11 3/8". Fix those errors in the points and create a new set of curves. Continue until all typos are corrected.
1. Look at the curves including using curvature combs for any major unfair portions. Also check to see how close the curves are to properly intersecting. Do initial fairing of the major edge curves: sheer, stem, keel/rabbet, transom edges, etc. Fairing curves may involve moving control points, use of Fair command and use of Smooth command. Frequently save and keep previous versions by iterating file name. After initially fairing the major edge curves the other curves are initially faired.
1. Look at the initially faired curves. See if any curves look fundamentally wrong. Refair any curves which have significant problems.
1. Create an initial surface using NetworkSrf, Loft or Patch. The choice of which method depends on the shape of the hull. Frequently the surface will extend beyond the edges of the hull to avoid major distortions of the surface. This requires extending the curves so that the resulting network of curves is â€śrectangularâ€ť. Patch is almost always used with an initial starting surface with edges which conform to the edges of the curve network.
1. Fair the surface. First step is to see if the surface can be rebuilt with fewer control points while staying close enough to the offset point. PointDeviation is used to check the differences between the surface and the imported offsets. Usual procedure is to first use Rebuild or FitSrf. In areas with tight curvature additional control points may be added using InsertKnot which should not change the shape of the surface. The surface with added control points is then used as the starting surface in Patch. Differences between the surface and offset points are checked with PointDeviation. Iterate until a surface with the minimum number of control points which can take the desired shape is found.
1. Move surface control points for final fairing of the surface. This is only done after the minimum control point surface is created. These moves of surface control points should be small.
1. Use Contour and DupEdge to create a new set of lines.

This was previously posted in a thread started by @bigjimslade in November 2015. 3d fairing

1 Like

Big Jim

Are you insisting in your Sweep 2 command for academic purposes, or whatever gets the job done is good enough? If the latter, then I too used the Curve Network and Sweep 2 commands, but used the given curves to create 3 different surfaces (yellow, green, blue). Below are my steps:

1. Changed units from feet to inches (abs. tolerance 0.001" - force of habit)
2. Split the curves around the yellow and blue surfaces
3. Used Network for green and blue surfaces and Sweep2 for yellow surface
4. Matched surfaces till zebras came home (donâ€™t know what I was looking for)
5. Merged surface into one (yellow bottom); poly-surface is also good
6. Intersected your curve network with my surface and the red lines show the intersection (larger picture)

Probably if you spend some more time you hit them (maybe if lowering the tolerance?).

Good luck

I would prefer to get the job done. What is the CURVE NETWORK comment?

Thx.

I meant surface from curve network command.

Ok, NetworkSrf

Hi Jim

Followed some of Davidâ€™s steps, faired your curves, added some more curves and used Sweep 2 command to build 2 surfaces, Then matched them and merged them. Surface is not as true to your curves as my previous post but the zebra stripes have less kinks now. See attachment.

Costel

Problem50_C.3dm (366.2 KB)