Thomm,
The 2004 US Sailing PN for the ARC17 is 70.0. This is the PN demonstrated by the ARC17 at the Tradewinds this past Jan. The spin was not used during the last four heats which were the only heats out of six that should be used in the PN calculations. During the first two heats there was much confusion on the race course and boats in the Open class sailed different courses and different numbers of laps due to not understanding the race instructions. If you correct this demonstrated 70 PN for the spinnaker, you get 67.3. That's pretty good for a boardless boat. The PN for this boat will settle down with more race data. This is one data point; the first data point for this new boat.
Good sailing,
Bill