Ed,

I'm no expert but I have played with this a little.

If when raking your spreaders you get more mast bend then it will make the mast less inclined to rotate down wind.

But as mark says. You can reduce your prebend so the mast will rotate better but in the same action stuff up the sail/ mast relationship and go like a dog on every other point of sail.

Another point that can limit mast rotation is where the diamond wires attach to the mast.

If this is too high up they will cross the sidestays when the mast rotates. This action effectively has to tighten the rig or stop rotating any further.

Depending on the class of boat there are limits where this attachment point can be.



I'm not advocating you change the attachment point for your dimonds just bringing this to your attention as another possible cause.



A possible sollution to this is rigging the boat a little looser in the first place but this can also have a side affect in as much as it can affect forestay sag on some boats which can have a detrimental affect on your boats ability to point.



I will send you an email of a video I have just taken of a positive mast rotation system that I have just put on my boat.

It may help, it may not.



Regards,

Phill