First some history ... which may not be completely accurate, but just what I remember. If someone else has a different story, please correct me.
The reason for the J+1 pole goes back to SORC(?) back in 78(?). The Johnstones took their new J/30 down to Florida. The race was done under IOR. In testing before the regatta they decided they went upwind just fine, but were slower than they'd like going downwind with their frac chute. So, they used an oversized pole, which allowed a bigger spinnaker. With a bigger pole, IOR allowed them to use a larger genny without further penalty. This configuration became standard for OD.
So along comes PHRF. How do you rate this relatively odd duck? Most PHRF stations will try to get a rating for the OD J/30 (J+1 plus oversize genny). For a PHRF J/30 (J length pole, 155% jib), they'll apply their usual penalties as credits. Often that's 3 sec/mile for the pole, and 3 sec/mile for the genny.
So, on Lake Michigan, OD PHRF = 138, "PHRF" J/30 = 144.
As an aside, I'd like to add that the method of applying the penalties as credits is probably overly generous. A penalty is generally meant to discourage change, costs more than it's actually worth. The difference in speed between a 155% genny and the OD genny is less than 3 sec/mile. Having said that, I'm not about to change my OD J/30 to play a PHRF rating game.
