Open-sea ship-to-ship transfer operation is an alternative way to avoid port congestion. This process involves a relatively small vessel which transports containers between the harbour and a large cargo ship equipped with a container crane. However, the presence of disturbances and uncertainties caused by harsh open-sea conditions can produce an excessive sway to the hoisting ropes of the crane system.

This paper addresses the problem of nonlinear discrete-time flatness-based controller design for a Permanent Magnet-Excited Synchronous Motor (PMSM). To eliminate the static errors of the system state variables and consider the nonlinear characteristics of a PMSM, a cascaded flatnessbased control scheme is proposed. Simulation results are provided to illustrate the effectiveness of the proposed control structures, in terms of better performance.

In stevedoring operations, the ship-to-ship transfer of containers in open-sea is becoming an alternative way to avoid port congestion and subsequently can increase port efficiency. This process involves a large container ship or a barge, equipped with a crane, and a smaller vessel which transports containers between the ship and the harbour. However, the harsh open-sea conditions can produce exogenous disturbances to the crane system during the load transfer. Besides, the uncertainties and disturbances in the crane systemmay degrade the control performance.