This paper discusses ship motions moored at a quay wall as the harbour calmness index. Cargo handling at a wharf may occasionally be interrupted and/or suspended if ship motions exceed the allowable ones. The wharf operation efficiency, then, should be defined based on the allowable ship motions for cargo handling in terms of the type and size of a ship and cargo handling equipment.
　In this study, we investigated instances of interruption and suspension of cargo handling due to ship motions for container ships and ferries. We then estimated the allowable ship motions for container ships and ferries through executing numerical simulations for each instance of interruption and suspension of cargo handling. We also evaluated and revised the estimated values respecting opinions of cargo handling operators, and finally proposed the allowable ship motions for container ships and ferries.