[RichH]

What Shaw meant was the mast should be straight up or 90° to the horizontal with little to no mast rake.

The OEM P30 mast without a 3/4" prebend ....
1. can easily develop 'mast pumping' at low wind speeds from the aft quarter ... the prebend changes the natural frequency of vibrations of the mast.
2. Sails made by a 'good' sailmaker will be already cut expecting that 3/4" mast prebend. Without the prebend the sail will set with more draft than needed .... prebend 'flattens' a mainsail. A P30 on the Chesapeake's normal conditions (10-15kts w/ 1-2ft of chop) will be much 'faster' and with less heeling with slightly flattened (speed shape) mainsail.

;-)