The PHRF penalty could vary from area to area. We use ours for one design only and haven't bitten the PHRF bullet. At the time we went to masthead spinnakers Carl Schumacher told us (1) the rig and boat are plenty strong enough to carry a masthead kite even in heavy downwind conditions and (2) the PHRF penalty would be 3-6 seconds/mile, in his opinion, depending on what we could negotiate. Our Detroit rating is 138 which works okay for us most of the time, so our local group decided not to rock the PHRF boat. When we sail in PHRF events we use class kites. This works okay, because both our class spinnakers and masthead spinnakers last longer, now, than when we were only using class spinnakers.

As I have posted before on this message board, you can make a trial masthead spinnaker simply by adding a panel to the center of a class spinnaker, and of course a masthead sheave and halyard. Last year in the NOOD the masthead spinnaker halyard came in handy when we broke our main halyard. We got the main back up quickly using

the masthead spinnaker halyard and only lost one boat. Not strictly one design but everybody in our fleet had masthead halyards and there were no out-of-town boats.