Hi Enrico, 30 cm is OK for 4.7 mē but may be a bit small with 5.3 at your weight and you may consider 32/33. Anyway both are very small fins for your JP. Most probably the main problem was caused by the sail, but once powered up you may discover that 120 L are quite cumbersome. Wide boards are stable in flat water but in the shore break they waddle here and there and do not help. If you have enough power in the sail you will enjoy a smaller board.
Last edited by Farlo; 6th January 2010 at 11:34 PM.