gauges made it possible to connect the cables after the installation of the chain stopper. To ensure a waterproof encapsulation and reliable protection, a dedicated epoxy cover was purposely designed and installed over the strain gauge and filled with resin.


The CTMS continuously monitors the ten- sion in the mooring lines at the OLT buoy and alarms the crew in case of line failure or overloading. Additionally the monitoring is important for post-processing the meas- urements for fatigue analysis. Alternatively, the fatigue analysis can be done automati- cally onboard.


Onboard fatigue analysis Based on TOTAL’s experience with the AHMS post-processing of measurements obtained from the hull of an FPSO (see page 6 for details), MARIN was awarded a contract to develop onboard mooring fatigue advisory software for the Moho Nord FPU, currently being built by HHI in Ulsan. In real-time, the software processes the load cell measurements from the Tension Monitoring System and explains any differences with design predictions. Differences may origi- nate from different conditions (environmen- tal and loading) assumed during the design process or from shortcomings in the fatigue design tool. The software is currently being developed and will be installed prior to sail away.


Position monitoring All projects men- tioned above concern newbuild projects, which means that the equipment can be


installed ashore while the chain stoppers are still above water. For this reason it is difficult, if not impossible, to instrument the chain stoppers of existing floating production systems without disconnecting the mooring lines. An alternative approach to alarm the crew in case of mooring line failure is by monitoring the position of the floating production system.


In previous years MODEC awarded MARIN a contract for the delivery of a Turret Position Monitoring System (TPMS) for the MV10, MV11 and Tullow TEN FPSO. The latter will be installed this year in the Deep Water Tano block, located offshore Ghana in about 1,400 m water depth. A highly accurate, long base, dual antenna system was installed on the wheelhouse outside the hazardous area with antennas placed on the bridge wings portside and starboard.


TPMS on the Tullow TEN FPSO


With readings of both position and heading the position is determined at the turret po- sition within a 0.4 m accuracy. The system was successfully commissioned in November 2015. In the figure the output of a TPMS installed in 2014 onboard another FPSO during actual line breakage is shown. In steps of one minute the figure shows the positions of the FPSO just before line failure and up to four minutes after line failure. The corresponding positions of the external turret are shown in red.


New developments TPMS is being further developed in the LifeLine JIP for applications on floaters, which exhibit wave


and wind induced offsets that have the same magnitude as offsets due to line failure. The methodology will be implemented in an onboard software tool, which processes the measurements and provides an alarm in case a mooring failure is suspected. The development will be accompanied by in service tests onboard two floating produc- tion systems. The project was just kicked off this April in Oslo during the FPSO JIP Week. Participants are still welcome to join.


Output of TPMS system onboard during actual line breakage


report


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