COMPARATIVE OFFLOADING STUDY BETWEEN CONVENTIONAL SHIP AND ATB (ARTICULATED TUG-BARGE)

The ATB vessels (articulated tug barge) were developed during the 70’s mainly for transport in rivers and lakes. However, in the last years, it is possible to note the increase of the interest for offshore application. As an example, ATB vessels could be used for FPSO offloading operations, working as an alternative to conventional shuttle ships.

The offloading operation demands special attention due to the proximity of the FPSO and shuttle tanker, and the motion dynamics of both vessels shall be well known and controlled to avoid accidents. With conventional shuttle SHIPS this operation has been performed for some years with success, but there are no known records of the use of ATB in such application. This work was performed to give a general idea about the dynamic behavior of the ATB as a shuttle vessel during offloading operation, in comparison with a conventional
SHIP.

The hydrodynamic forces and motions of both vessels were evaluated and several simulations, in different environmental combinations, were performed. It was also prepared sensitivity studies about the loss of the propellers. In all conditions the hawser force and the position of the shuttle were measured.

At the end of the analysis it was not observed big difference between the use of ATB or conventional shuttle SHIP in offloading operations.