The Northsea terminal is a busy container terminal in the port of Antwerp which is located in the tidal river Scheldt along the navigation channel. At this terminal multiple deep-drafted container vessels in the range of Post Panamax up to Ultra Large Container Vessels berth on weekly basis. On the other hand, all seagoing vessels coming to and leaving the port of Antwerp pass this terminal. All passing vessels cause a displacement of the water resulting in forces working on the moored vessel. The size of these forces are dependent on the passing speed, the passing distance as well as the dimensions of the passing and the moored vessel [1]. The mooring lines as well as the fenders will try to absorb the forces working on the moored vessel, however the latter one will experience some motions due to the elasticity of both mooring lines and fenders.
The Northsea terminal was designed and built in the 1990’s. However, due to economies of scale in the container vessel industry, the sizes of the seagoing vessels have increased a lot during the last 2 decades resulting in a situation which is different from the design phase. As such, the Antwerp Port Authority executed a full-scale measurement campaign at the Northsea terminal, the terminal in the port of Antwerp which is most exposed to ship-ship interaction effects. During a period of 3 months the motions of all moored container vessels larger than the Panamax class at this terminal where measured using 2 dGPS instruments mounted on board of the vessel. All information about the vessels passing the terminal, as well as the wind and the current conditions were monitored as well.
Analysis of this large dataset revealed some interesting results. First of all the importance of pre-tension in the mooring lines, which is challenging to obtain at all times in a tidal environment where it is not allowed to use auto-tension, was clearly seen. Secondly a clear difference in observed motions of the moored vessels was seen in relation to the quality of the mooring lines being used. Where the minimum breaking load of the mooring lines is always in agreement with the guidelines set out by IMO, there is no such regulation about the elasticity of the mooring lines. As such, a large difference in elasticity has been found, where a larger elasticity clearly results in larger motions of the moored vessel. Even with good pre-tension on the mooring lines, some vessels with mooring lines with an elongation at break of more than 30% showed rather large motions.
In order to guarantee the safety of the terminal operations at all times, it was investigated whether the so-called ShoreTension system could minimize the motions of the moored vessels equipped with elastic mooring lines. The ShoreTension system is a dynamic mooring system developed to assist large container vessels to stay safe at the quay wall during extreme wind loads. The system is used in addition to the regular mooring lines. During a period of 3 months, the motions of moored vessels equipped with the ShoreTension system were monitored. Different configurations have been tested in order to find out what is the most optimal configuration. The full-scale measurements have proven that the ShoreTension system can help in reducing the motions of the moored vessels considerably, however guaranteeing the pre-tension in the mooring lines at all times remains a necessary condition for safe mooring even with the ShoreTension system.
[1] TALSTRA, H.; BLIEK, A.J., ‘Loads on moored ships due to passing ships in a straight harbour channel, PIANC world congress, San Francisco, 2014.
Statement:
Due to economies of scale in the shipping industry on the one hand and expansion of ports due to increasing maritime traffic on the other hand, ports are often facing more as well as more intense ship-ship interaction effects. This might affect safety of port operations, which is of crucial importance for many ports.
With an extensive full-scale monitoring program, the Antwerp Port Authority investigated the effects of ship-ship interaction at one of their most exposed container berths. The effectiveness of the newly developed dynamic mooring system called ShoreTension was also for the first time tested for the purpose of ship-ship interaction effects. The results of this monitoring campaign will have the interest of both port authorities, as well as consulting companies involved in the design of port facilities.