I used to race a P30. For the best output set the capshrouds at 15%, the forward lowers at 18% and the aft lowers at 12%, Initially set the backstay at 15%.
the 18% forward lwr / 12% aft lower tensions will give the mast a correct 'pre-bend' (forward bow) of approx. 1/2" .... the approx 1/2" forward bowing is important no matter what tension is in the rigging.
Then go sailing on a hard beat in approx. 15 kts. to be sure the mast stays straight and without any side bowing. Make corrections as needed.
To set the correct tension in the backstay according to the day's conditions: http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf
.... but no more than 30% tension for long periods of time. When done sailing for the day, reduc
e backstay tension to ~15%.
FWIW - a boltroped dacron mainsail on a P30 requires about 3 extra inches of luff stretch via the main halyard to attain correct sail shape. Raise the main full up, then apply approx 3 inches of extra halyard strain.
You want the P30 set up so that you get only very 'slight' so-called weather helm ... or about needing only 3° of rudder angle to keep the boat on a hard beat in 15kts.
Here's the correct way to raise a dacron mainsail on just about any boat: How to properly RAISE a woven dacron mainsail - SailboatOwners.com