The paper describes the dynamic positioning aspects of a novel solution for offshore loading. A site-resident floating unit is equipped with a DP system and equipment for oil transfer. When a tanker calls at the loading site the unit is attached to the tanker and keeps it on station during the loading operation. The concept relies on the system's weathervaning ability. The mean heading relative to the weather is important for the mean environmental loads and the positioning ability. Also the positioning stability is important. The criterion for static stability is easy to establish. Two examples demonstrate how static stability depends on the weather conditions. A dynamic stability analysis is difficult to carry out, due to the strong dependence on the directions of current, wind and waves. To check the positioning performance of the system model tests have been carried out using characteristic weather states of Brazilian and West African waters. It was found that the weather-vaning dynamic positioning was very satisfactory. From the tests the required capacity of the thrusters could be estimated.
Loading of transport tankers from offshore storage buoys, FSOs or FPSOs is frequently carried out by means of single-point mooring, submerged turret loading (STL), SALM or DP assisted tandem loading. Common to these solutions is the use of tankers that are adapted to the offshore terminal, or a need for assisting vessels such as tugs.
A new and different solution has been developed, which does not set any particular requirements to the tankers. As a consequence, any OCIMF compliant tanker can call at the terminal. This solution is referred to as the HiLoad Technology. The idea is to use a freely floating unit that is equipped with hoses for loading of oil and thrusters for manual and automatic positioning (Fig. 1).
