ABSTRACT

Throughout the history of fendering system design assumptions have been made on the magnitude of the hydrodynamic added mass of ships when hitting a fendering system. This added mass is known to be dependent upon a number of variables, such as ship shape, ship size, bottom clearance, spring constant of the fendering system, mode of collision, etc. The assumptions to be made for the fendering design are in general not supported by a theory backed by extensive experiments. In view of the increasing amount of structures of various kinds in several offshore areas and the increasing transport of dangerous cargoes, the demand for reliable design methods gets stronger. It is the purpose of this paper to give more data-based support to the design of fendering systems by means of the presentation of an extensive test series conducted at the Netherlands Ship Model Basin. Correlation with existing theories are being discussed.

INTRODUCTION

Berthing of ships has always been a matter of experience of captains and designers. For rather small ships this appeared to be acceptable. However, with the increase in size of ships during the last decades, extrapolation does not give the right answers. Larger ships tend to berth at very low speeds (see Kikutaui [8]). So low actually, that visual estimation is not very well possible and berthing terminals have to be equipped with distance and velocity indicators. Despite this equipment, sometimes things go wrong and large material damage is the consequence, since the inertia forces during these operations are enormous.

The approaching speed of ships has been subject to study and results on this subject have been published J.U. Brolsma et al. [1], [2] and others. They give a certain frequency distribution for the approaching speeds of large ships. This gives the designer a tool to accept a certain probability level and work with a certain design velocity. The other important factor in fender design practice is the total mass one has to consider. This total mass is governed by the following parameters:

• vessel size;

• vessel's draught;

• underkeel clearance;

• fender Characteristics;

• berthing modes;

• berthing velocities.

Most of the current design methods to determine the amount of hydrodynamic added mass do not take into account all of the above-mentioned parameters. The most common practice is, that a constant amount of added mass is applied to the ship's mass, independent of all mentioned effects. See Saurin [3] and Vasco Costa [4]. Thoresen [5] takes into account possible eccentricities during collision, while Giraudet [6] only accounts for the underkeel clearance.

A more advanced computer program dealing with all mentioned parameters has been developed at the Netherlands Ship Model Basin. This program was presented at the OTC by van Oortmerssen in 1974 [7]. To provide more data to check this program and to supply potential designers with more test results to support initial fender and jetty designs, it was decided to start an ambitious test program covering all mentioned parameters governing the hydrodynamic added mass.

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