Safe mooring of large container ships at quay walls subject to passing ship effects

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Safety of container ship (un)loading operations in the Port of Antwerp : impact of passing shipping traffic

Purpose Economies of scale drive container ship owners towards ordering larger vessels. Terminals need to ensure a safe (un)loading operation of these vessels, which can only be guaranteed if the mooring equipment is not overloaded (lines, fenders and bollards) and if the motions of the vessel remain below set limits, under external forces. This paper aims to focus on the passing vessel effect as a potential disturbing factor in the Port of Antwerp. Design/methodology/approach Motion criteria for allowing safe (un)loading of container vessels are established by considering the container handling process and existing international standards (PIANC). A case study simulation is presented where the behaviour of the moored vessel under ship passages is evaluated. Starting from a representative event, the effect of changes in passing speed and distance is discussed. Findings The study illustrates the influence of passing velocity and distance on the behaviour of the moored vessel, showing that when passing speeds are higher and/or distances lower than the reference event, safety limits are potentially exceeded. Possible mitigating measures, including the use of stiffer mooring lines and/or a change in arrangement, are discussed. Social implications By restricting the motions of the passing vessels, the focus and general well-being of the crane operator is enhanced, as is the safety of workers. Originality/value The paper provides a unique combination of container fleet observation, safety criteria establishment and case study application

Wind modeling for large container vessels : a critical review of the calculation procedure

With the increasing size of container ships, accurate methods to model manoeuvring and mooring conditions are indispensable. Especially in confined waters, where the ship speed is low or even zero, wind forces add a significant contribution to the force balance. The calculation of wind forces is typically done using wind coefficients based on wind tunnel tests. In these computations, a reference wind pressure must be used which is often based on the wind speed at 10 m height. When the wind blows over a rough surface however, the wind profiles become non-uniform, resulting in much higher wind speeds near the top of the ship, for the same wind speed at 10 m height. In case of differences between the wind profile used in the wind tunnel and the one expected in the reality, an appropriate reference pressure should be used. A method proposed by Blendermann to calculate such reference pressure is applied in this paper to a wind force calculation for an ULCS. It is shown that, depending on the roughness of the surface, the reference pressure can be a factor 2 to 3 higher than the one corresponding to 10 m height. This means that wind forces are potentially highly underestimated. The results of the method are compared with CFD simulations with a uniform and non-uniform inlet profile. The comparison shows a good agreement between Blendermann’s method and CFD results for the surge force and roll moment. On the other hand, Blendermann’s method seems to overestimate the sway force, but more simulations are needed before a firm conclusion can be draw

Wind modeling for large container vessels : a critical review of the calculation procedure

With the increasing size of container ships, accurate methods to model manoeuvring and mooring conditions are indispensable. Especially in confined waters, where the ship speed is low or even zero, wind forces add a significant contribution to the force balance. The calculation of wind forces is typically done using wind coefficients based on wind tunnel tests. In these computations, a reference wind pressure must be used which is often based on the wind speed at 10 m height. When the wind blows over a rough surface however, the wind profiles become non-uniform, resulting in much higher wind speeds near the top of the ship, for the same wind speed at 10 m height. In case of differences between the wind profile used in the wind tunnel and the one expected in the reality, an appropriate reference pressure should be used. A method proposed by Blendermann to calculate such reference pressure is applied in this paper to a wind force calculation for an ULCS. It is shown that, depending on the roughness of the surface, the reference pressure can be a factor 2 to 3 higher than the one corresponding to 10 m height. This means that wind forces are potentially highly underestimated. The results of the method are compared with CFD simulations with a uniform and non-uniform inlet profile. The comparison shows a good agreement between Blendermann’s method and CFD results for the surge force and roll moment. On the other hand, Blendermann’s method seems to overestimate the sway force, but more simulations are needed before a firm conclusion can be draw

A mooring arrangement optimisation study

Ports want to ensure safe and reliable loading operations for all ships. Increase in ship sizes, especially container ships, potentially cause unsafe mooring situations. For ships moored at quay walls, there is also a lack of international guidelines for mooring arrangements. This paper presents a case study for a moored containership being passed by a vessel of identical dimensions. The behaviour of the moored ship is simulated using UGent’s time-domain mooring software Vlugmoor. Starting from a well-balanced arrangement used in daily operation, three optimisation steps are presented, aiming at lowering the ship motions, which are critical. The first step explores the impact of changing line positioning to reduce line length disparity and improve efficiency in critical force directions. The second step considers a lower fore mooring deck to reduce line steepness, as well as additional winches below the bridge and funnel. The third step proposes replacing medium stiff lines with a very stiff HMPE line, combined with an elastic tail. The effect of these optimisation steps on the ship motions are presented and compared with predictions based on efficiency parameters, expressing the capacity of the configuration to deal with positive and negative surge forces. It is shown that applying these optimisation steps can significantly improve the safety of a moored container ship during a ship passage