Does the convex decomposition only work for water tight meshes?

[Levi-Armstrong]

The reason I ask is I have tried this on a surface mesh of a car which is attached. At first it just sat on "Filling Holes" indefinitely then I removed this operation and recompiled and it will now decompose the geometry but in to a single convex hull.

car.obj.gz

[gaschler]

Does the convex decomposition only work for water tight meshes?

The step after "filling holes" is a (rather simple) voxelization, and that does require a water tight mesh.
Maybe our "filling holes" algorithm is too simple for your case.
You could try to make your input water tight with a more elaborate method (perhaps Meshlab is better) and use that as an input.
If the convex decomposition CLI tool doesn't find holes, it won't spend time on that step.

it will now decompose the geometry but in to a single convex hull.

This is unrelated and should depend on mostly on the parameters.

./bounding-convex-decomposition [options] filename [filename_out.wrl]
--alpha, -a: Parameter alpha, default is 1. Increases the number of splits into convex bodies.

Even if you have very long triangles, the algorithm should be able to split them up into multiple convex segments.

Hope this helps.