RE: Severne Overdrive 2005 rotation problems
Spacing out the camber is not the way to go on this sail. We do have a lot of rotation on this 10.0 Overdrive 2005 on the bottom batten especially.
Don't put any spacers on; it will only make it worse. You might need to cut/ sand some material (3-4mm) of the bottom camber to make the rotation better.
Take the camber out of the sail. Cut with a hacksaw 3-4 mm of the camber end that is pressing against the camber tongue/ and panel inside the luff sleeve.
If your camber has a bolt in it, then remove it, to prevent the camber tongue to hit it.
Rig your sail and check the rotation, let me know if it still has problems.
We did redesign the 10.0 in 2006 (your brothers sail) and made the rotation a lot smoother.