For the design of fenders and dolphins it is essential to have available an adequate method to describe the berthing manoeuvre of a large tanker to a jetty. Such a method should result in a prediction of maximum load in the dolphins, departing from a certain dolphin elasticity and lateral speed of approach of the tanker. The calculation method generally used up till now is based on the assumption that the kinetic energy of the tanker when it touches the fenders has to be absorbed by the fenders. In fact, this approach is based on an equation of motion with a constant added mass coefficient and zero damping. The choice of the added mass coefficient has always been a problem due to a lack of data, especially where the added mass in shallow water is concerned. In this paper, data are presented on the added mass and damping of large tankers in shallow water. These data were obtained from experiments (forced oscillation tests). From these data it appeared that it is not justified to use a constant (time-independent) added mass and damping coefficient. Therefore it is suggested to use the equations of motion according to W.E. Cummings, which employ impulse response functions. Data on these functions are presented for large tankers for different keel clearances, which can be used for practical applications. An example is given how to use the data for the prediction of maximum fender loads and the results of the calculations are compared with measurements, obtained from model tests.
The introduction of very large ships for the transport of crude oil has brought along a lot of engineering problems. One of these problems is the design of terminals for such large ships. To be able to design for instance a jetty it is of vital importance to have knowledge of the loads which are exerted on the construction by the moored ship, under influence of wind, waves, passing ships etc. but the impact forces occurring during the berthing of the ships may be of equal or even greater importance. A considerable amount of money is spent each year on repairing damaged mooring facilities. The origin of most accidents which cause this damage is twofold. A great deal of damage must be attributed in the first place to the lack of knowledge and reliable methods to calculate the impact forces. On the other hand, human aspects play an important role. It will be obvious that damage will occur when the approach speed of the vessel is too high. For the pilot it is very difficult to estimate the speed of approach, and therefore systems have been introduced to provide the pilot with information on the movements of the ship. The phenomena, occurring during the berthing manoeuvre of a large ship, are complicated, and the fender loads are influenced by a lot of parameters: the size of the ship, the elasticity properties of the fenders, the speed of approach, forces exerted by tugs, wind, current and waves, mode of motion (in general translation combined with rotation), the underkeel clearance, proximity of banks, if any, and rigidity of the hull of the ship.