Near the offshore production platform Vega A, the tanker FSO Leonis is moored to a steel column with circular section, 130 meters high and 10 meters in diameter, installed in 1988 in the Sicilian Channel, the connection is via a bridge structure (yoke) with welded steel sections that make up the system SPM (Single Point Mooring). The structural system in steel box girders and column, with its cylindrical hinges, is calls-to the actions of the sea that induce cyclic stresses and fatigue. The document presents the improvement strategies of the monitoring system of the structure that connects the ship to the column, originally installed in October 2009. The original monitoring system is composed of strain gauges sensors, in fiber optic, and inclinometers biaxial that detect rotations of the column and the bridge. New gyro on the tanker FSO and optical thermal sensors on yoke are installed, and a new control unit will allow, together with the inclination data, to verify the ship's pull on the column. The new control unit will have a high acquisition frequency that will allow us to investigate the structural modes shape of the system and yoke. The results allowed us to evaluate the conditions assumed in the project and made it possible to define a program of inspection and maintenance of steel structures.