In the present paper the hydrodynamic loads working on buoys which are used as single point mooring terminals are dealt with. A proper insight in these loads is a necessary basis for estimating the motions of a buoy system installed in waves. Such an estimate can be very helpful both for optimization purposes in the design stage of a new system or to explain observed phenomena of existing systems.

To obtain insight in the oscillatory hydrodynamic loads working on a buoy, the loads are split up into a number of parts. For each part an attempt is made to give a proper estimate, demonstrating the influence of the main parameters of the buoy. The thus obtained estimated loads are compared with the results of exact computer calculations and with the results of model -tests when available. The results presented are mainly related to cylindrical buoys used for Catenary Anchor Leg Mooring systems (CALM), but the described procedures can be used for other types of buoy systems too, such as SALM (Single Anchor Leg Mooring) systems or systems with stiff vertical legs. The effect of a skirt, with which most CALM buoys are fitted, is shown.

Finally-an example is given, how the motions of a CALM buoy in a not too severe sea state might be estimated when there is no tanker moored to the buoy, using the computed hydrodynamic loads. The results are compared with the results of some model tests.


Mooring buoys have been installed at many locations all over the world during the last ten years. They are mainly used as oil terminals for large crude carriers when no use can be made of existing harbors. This can be due to the fact that the dimensions of existing harbors are not sufficient for the big ships or that the tankers have to load oil at a location where no harbors exist (e.g. terminals in the deep waters of the North Sea). As a result of this most mooring buoys have been installed at rather exposed locations and are subjected to the action of wave, wind and current.

One part of the problem is formed by the wave induced motions of the buoy system. Information about these motions is not only of importance to judge the survival ability of the system, but also to investigate fatigue and wear and tear problems in hoses and anchoring systems. To contribute to this subject the present paper deals with the oscillatory hydrodynamic loads on floating, cylindrical buoys. Most data presented are related to Catenary Anchor Leg Mooring systems (CALM). An example of such a buoy, used during some model test programs, is shown in Figure' 1. However, the procedures described can also be applied for other systems, for instance SALM systems. The effect of a skirt, with which the CALM buoys are fitted, will be dealt with.

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