The Influence of Passing Ships on Ships moored in Restricted Waters

Abstract Ships moored in harbours are subjected to hydrodynamic forces due to other ships passing nearby. Such forces induce motions of the moored ship which may hinder loading/discharging operations or cause damage to the mooring system. These forces, sometimes known as suction forces, are associated with the primary pressure system around the sailing vessel which acts upon the moored ship. In this paper some of the aspects which play a role in effects due to passing ships will be treated. In order to do so, two computational methods developed by the first author to predict the low frequency forces due to a passing ship will be used. The first of these is based on implementation of the so-called 'double-body' flow method previously introduced by other authors. The second, newly developed, method applied in this paper predicts passing ship effects also taking into account free surface effects due to the passing ship and the additional forces these exert on the moored ship. Results of both computational methods are compared. Full scale tests were carried out by Svasek Hydraulics and MARIN on behalf of the Port of Amsterdam. These tests involved, among others, measurement of the mooring forces of a fully loaded barge during the passage of large vessels in the Noordzeekanaal which joins the Port of Amsterdam to the North Sea. Results of these measurements are compared with computations. Finally, an unusual case involving the generation of solitary waves by a vessel in a canal is treated. Introduction Passing ships create disturbances in the water which result in forces on other ships and floating structures. Such hydrodynamic forces can result in high mooring forces and unacceptable motions of the moored vessels. In extreme cases, mooring lines of ships have parted which in one case, see NTSB report [1], resulted in loss of life and total loss of the moored ship due to fire. Such cases are extremely rare but hinder and damage due to passing ship effects are a regular feature of life along the waterways and in harbours. With the increasing awareness of and decreasing tolerance relative to personal injuries, environmental impacts and damage to facilities and ships, more attention is being focussed on evaluation of such effects whenever major changes are made with respect to the vessels plying the waterways (larger, faster), the waterway geometry or traffic volumes. At the Delft University of Technology research has been conducted into methods to predict the effects of passing ships on moored vessels. Such effects have in the past concentrated on suction effects associated with the primary or "doublebody" flow around the passing vessel. See, for instance, King [2]. By definition, this means that real free-surface effects, i.e. surface wave propagation effects, are not accounted for. The reason for basing the effects of passing ships on double-body flow models is that generally such ships are moving at low Froude number values, even when viewed in relation to the waterdepth.