Yes, I'd rather use OnCollision since it's in Unity and features continuous collision, but ... I've been developing the thing using OnTrigger and now when I go back to OnCollision the ships abruptly looks down ... The old hovering alignment works if I make it 100 times more powerful but then the ship is incredibly stiff

Anyway, it's obsolete so I must code something new. Been thinking and I guess I know the cause : joint orientation. I'll see if I can make it play nicely with user pitch up/down and the torque with .TargetRotation property. Hopefully if it works then the problem will be fixed at this point.

If not then, that was my first question regarding the formula for bouncing with OnTrigger, been using this cheap algo but it's really bad:

Code:
var yVelocity = Mathf.Abs(transform.InverseTransformDirection(_shipBody.velocity).y);
 _shipBody.AddRelativeForce(_shipBody.transform.up * yVelocity * 2.333f, ForceMode.Impulse);
Otherwise regarding your tips:
- barycenter : OK
- plane : OK
- triangle search : OK (I guess since I can track the ship's section quite well now)
- other things : I guess OK

So I'll definitely dig into this approach if all else fails.

Coming back to post my results !

Thanks