The paper deals with some preliminary results of model tests carried out in the wave and current laboratory of the Netherlands Ship Model Basin to determine the external forces on a tanker, moored in shallow water, as a result of the passage of a large tanker shaped vessel. The main effects of passing distance, speed and size of the passing tanker are shown.

It will be discussed how the response of the moored vessel may be calculated from the exciting forces measured.

A calculation of the lateral motion of a tanker moored by means of linear springs illustrates the calculation procedure and supplies interesting information concerning the effect of the stiffness of the mooring system on the lateral mooring forces.


The interaction of ships sailing in close proximity to each other is a phenomenon which plays a role in the handling of ships both in confined and unrestricted waters.

Situations where the interaction of ships is important are for instance:

  • the replenishment operation in open sea and deepwater; see ref. (1).

  • the determination of the feasibility of lightering of V.L.C.C. 's under way in both deep and in restricted water.

  • the overtaking and passing manoeuvres of two vessels in a canal or in a restricted waterway.

  • the forces on a moored vessel due to the passage of other vessels

All of these problems and phenomena have been in existence ever since the day man took to the water in ships. However, it is the rapid growth in the size of the vessels and in their speed which has considerably increased these interaction problems. As a result of these developments the Netherlands Ship Model Basin has become involved in a number of studies on the fore mentioned subjects. Among these studies were various investigations into the phenomena occurring during the passage of a large tanker in close proximity to a tanker moored to an oil loading terminal. Due to the deep draft of the tankers a number of terminals are located quite close to natural or man-made waterways. This results in small passing distances between the moored vessel and the regular traffic on the waterway.

Another factor which tends to result in large interactions is that the speed of the large tankers, passing a moored vessel, is limited to a certain minimum to ensure sufficient maneuverability.

Both factors lead to an increase of the forces on the moored ship due to the passage of another vessel.

The general purpose of the fore mentioned model test studies on the passing ship problem was to obtain answers to the following questions:

  • What is the permissable speed and distance of a tanker, while passing a moored vessel, with regard to keeping the loads in the mooring system and the motions of the moored ship below certain acceptable values?

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