“Rospo” is an offshore oil field producing since 1982 located off the coast of Pescara, Italy and operated by Edison. Offshore facilities include 29 production wells connected through sea lines to 3 platforms and to a FSO vessel permanently moored by a turret anchored with 6 chain lines to the sea bottom. The Suezmax 140.000 dwt FSO “Alba Marina” was utilized since 1987. This “single hull” tanker was no longer fulfilling the present European Environmental Marine Regulations requiring “double hull and double bottom (DH/DB)” configuration. For this reason Edison is replacing the Alba Marina with a new DH/DB Aframax tanker converted into a FSO. The disconnection of the FSO has been preceded by inspections and analysis of the mooring structure to evaluate its compliance with the most recent regulatory requirements. The inspections and analysis have confirmed that the structure is very well preserved and that it is still adequate to fulfill the offshore codes requirements, with the need of only minor substitutions. These results supported the decision to maintain the old turret connecting it to the stern of the new FSO. The comparison between the conclusions of the original 1987 design and the results of the present numerical analyses shows the power and accuracy of the analytical methods adopted in the past. The use of rational structural schemes and reliable design manuals (e.g. “Roark”, ref.1), allowed to obtain a correct understanding of the structural behavior. These results are even more impressive considering the calculating tools available at that time.