PurposeEconomies 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/approachMotion 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.FindingsThe 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.Research limitations/implicationsThis paper serves as a basis for future research on safety criteria and optimisation of the mooring equipment and configuration to deal with passing vessel effects.Practical implicationsThe presented results can be used by ship and terminal designers to gain familiarity with passing vessel effects and adopt suggested best practice.Social implicationsBy 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/valueThe paper provides a unique combination of container fleet observation, safety criteria establishment and case study application.