Smoothing Hull Forms

I have a hull I have been working for quite a while. It’s pretty smooth. Lines are knuckles. The hull form takes on a number of different configurations along its length.

In this area things get difficult.

I have to break this area into a lot of small sections in order to get four-sided surfaces.

I end up with a a number of small irregularities at the surface boundaries.

Is there any good way to smooth these out?
Or should I just accept that this is as smooth as this is ever going to get (smoother than the real thing)?

hi @miano you are on discourse for a while now, why dont you post the relevant portion of the mentioned area, just explode the hull and post the lower part if you dont want to share the entire work, otherwise its just guessing games. it could also be render mesh issue which is not refined, really difficult to say without having a closer look

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If you want to look at this problem area, I have extracted it for size.

problem (921.4 KB)

Keep in mind that:
(1) I am working off plans. The shape is what it is.
(2) I am working with others. My stuff has to fit what others are doing for the interior.
(3) The rest of this hull looks pretty normal. Just horizontal and vertical frames.
(4) The cutout at the left is to transform a 3-sided area into 4-sided.
(5) The entire bottom edge and the descending edge (except for the shaft bossing surface) all join to half siding. Some of of the surface edges are chosen so that corners in the hull match up to surface corners.

dear Miano

why does your file has a 0.001 degree document tolerance ?

one of this wavy-artefacts in your surface is caused by the control-polygon.
two rows form some unexpected order (1-3-2-4) - there is some kind of x-shape-self-intersection (not sure if there is a official, nicer term for this)

not an expert in ship-hulls and inch-based modelling - but for me the CV / Span count seam s far beyond what is necessary, to define a shape like this.

Also the curvature is locally reversing several times (graph going up / down).

I did not find a fast and really nice repair.

but 2 approaches that might point you in a suitable direction:


_EdgeSrf (as a start)
_rebuild (to single or very few spans)
do several loops of:
_matchSrf (keep Isocurve-Direction, no refine)
manual CV-Editing
_insertKnot (stepwise, to locally freeze surface design)

finally do a last _matchSrf with refine on

search this forum for _matchsrf and massage


use NetworkSurface with small amount of inner curves, only in one direction
example with 2 inner curves

problem surves_tomp.3dm (444.1 KB)

hope this helps -tom

The tolerance is just the default in the file I copied to.

The original is 1/32".

In regard to that crossing of points, that surface was created using sweep 2 with only the rails at the top and bottom and the only frames at the sides.

The number of control points seems to grown in this area as I do more matching to surfaces.

It appears that each matchsrf increases the density. The density is somewhat high to begin with as I have 40 vertical control points (rebuildcrvnonuniform to 1/32") in the first segment. As I work to the area shown here from both ends, the density grows.