An interesting article was just published by AM bests on the P&I market.
You will find it at http://www3.ambest.com/Frames/Frameserver.asp?site=press&Tab=1&altsrc=2&RefNum=66496956834984573854
Over time if the P&I club does not collect enough money up front, that forces more money into the supplemental calls down the road. It is the old balloon trick – squeeze one end and it gets larger at the other!