Surface slip line not calculated accurately in some instances. #41
Description
Line 30 in 3e4e690
The slip line approaches to the surface normal under certain conditions. We're not sure why yet, it may be an issue with the segment velocities of screw segments. Look at how aligned the velocity is with the line direction. This is the thing that goes wrong most often when decreasing the line drag. It may be the case to removing the velocity such that the only velocity taken into account is the component perpendicular to the line direction.