Wouter and Eric, thanks for the clarifications and tips, very helpful indeed.

Eric, your comment on rig tightness effecting rotation makes perfect sense; obviously you can feel that when you manually rotate the rig in no wind after chaning rig tension. Also, sometimes the rig rotates freely to a point and rotates a little further only when significant force is applied so it must be wind strength dependent as well when the rig is stiffer.

Wouter, does a tighter OH induce more rotation because the mast pushes harder on the back of the mast?

A few more rotation issues:

Do you guys think that more bent masts (whether prebent or via DH/mainsheet) rotate more easily than unbent masts (all other factors being equal)?

In your experience, does increased mainsheet tension increase or decrease rotation, all other factors equal?

Finally, from looking at the forces of the spi on the mast top (admittedly very crudely) it actually looks like the spi's pull on the mast acts to de-rotate it, as opposed to the main's pull which acts to induce rotation. The overall net rotation you get looks to depend on that balance although the pull of the spi would be entirely wind strength dependent whereas the main forces would be a combination of mainsheet tension and wind stength dependent. Does this make any sense to you? Maybe these factors can be used when sailing to tweak mast rotation under varying wind conditions?

Jerry