Heavy Marine Transport is a well accepted method to move large heavy offshore related floating structures around the world. This type of transport is normally limited to getting from and going to sheltered locations, where loading and discharge operation of these objects are safely carried out in very mild environment. However, there is an increasing demand for loading and discharge at offshore locations; and as these operations are sensitive to environmental criteria, this has consequences for the scheduling issues. Also, with increasing size and weight of offshore structures and the desire to deliver these objects directly to remote offshore location, larger Heavy Transport Vessels are required, which may need to operate in higher sea-states than presently considered safe. These safe conditions are mainly based on long term experience. Assessment of the hydrodynamic behavior of submerged HTVs and cargo in rough seaway, in short Offshore Loading / Discharge, will contribute to extending the scope and operability of HTVs. Also, this investigation will contribute to safety by creating more insight in heavy transport operations. Research and development projects in the past have dealt with many aspects of Offshore Loading/Discharge. Both the basic design (of both HTV and systems) and hydrodynamic behavior are investigated. Problems were encountered in the area of predicting the relative behavior of floating structure above a HTV. Investigations have shown that inaccuracy is mainly caused due to the narrow gap between cargo and HTV. Development of an accurate, quick and cost-effective method for the prediction of hydrodynamic behavior of cargo floating above a HTV is in progress. This paper is presenting theory and limitations of an adapted multi-body diffraction theory. The adapted theory uses different domains in which different solution methods are used. For the flow in the gap between cargo and HTV, a 2D solution is used, whereas for the outside domain standard 3D potential solution is applied.
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