A book I checked out from the library recently called _Looking at Sails_
claims that on the fractional rig, like the Potter, the mainsail is the
primary driver and best performance will be achieved is the jib is trimmed to
enhance the drive from the main, rather than provide max. drive from itself. I
interpret this to mean that you shape your jib to optimize the slot. On my
Mk.II this has also meant experimenting with different length tack pendants
(the little piece of cable between the tack of the jib and the fitting on the
bow) so that the leech twist of the jib matches the "belly" of the main.
Another thing that can influence windward performance is the angle of attack
of the underwater surfaces. When going to windward you want to feel just a bit
of "weather helm". This indicates that the attitude of the boat is such that
the underwater surfaces are generating lift to windward as they move through
the water. If the genoa keeps pulling the bow off the wind and you have to
keep steering it back up then hydrodynamic forces of your centerboard and
rudder are likely working against you.
_Looking at Sails_ also points out that on the rigid, masthead rigs (like you
might find on the Catalinas and Coronados that you mentioned) the jib is the
primary driver of the boat and the main is trimmed to balance the boat - so
what works best when you sail on your friend's boats may not translate
directly into good performance on your Potter.
Hope this helps!
Dave Kautz
P-15 #1632 Tilly Lucy
Palo Alto, CA