tshan:

I think if you need positive rotation on your mast then maybe some rethinking about your setup is in order. I have not seen a posirotation system on an F18.

Maybe sailing way to low if you need the mast out that far. Most of the time the sheet will be pretty tight and the traveler closer to center than not. The force of the main sheet will probably be enough to push the boom forward, pushing the mast to where your rotation line is loosened to.

If you sail in lots of light wind and have to sail down wind in some long channel then maybe a rotation system is in order.

Dan