This paper proposes a procedure to quantify dangers of maneuvering ships in ship-to-ship lightering operations. In the previous study, operational limitations as a function of 2-D intra-ship position, due to static mechanisms of hydrodynamic interaction were proposed. The dynamic evaluation of danger based on maneuver simulations is implemented in the present paper, which focuses on the difficulty of maneuvering. An automatic control system for following a trajectory given in a relative coordinate system is applied and the mean deviation from the trajectory is recorded with changing initial intra-position. It has been confirmed that maneuvering difficulties may change depending on the intra-position of the ships in commencing the final approach, as well as loading conditions. These results are considered to contribute to improving safety in performing this operation.
A ship-to-ship (STS) lightering operation is a cargo transfer from one vessel to another, with both ships engaged and advancing at slight speeds. This operation is time- and cost efficient, but entails a higher risk of steel-to-steel contact due to sudden and unpredicted motion caused by hydrodynamic interaction between both ship hulls. In order to reduce this risk, a lot of knowledge related to STS operations has been accumulated and safety guidelines have been developed up to the present (OCIMF 2005). Consequently, STS operations are nowadays regarded as a medium-risk operation. For further enhancement of safety during STS operations, the authors have been working on developing a decision-support system for use by the ship officer in charge of the STS operation, based on measurement of relative positions and motions of the ships involved (Yoo et al. 2009 and Husjord et al. 2011). In addition, the authors also aim to improve this system by introducing the concept of safety/danger information related to hydrodynamic interaction between the two ships.
