Design Aspects of Green Water Loading on FPSOs

Green water is a significant problem for floating ship-type offshore structures, which needs to be assessed in the early design of the structure. First the present paper summarises a new semi-empirical design evaluation procedure that can assist in this design process. Then the practical design considerations related to the green water problem are discussed. There are different ways to solve the green water problem for a particular structure at a specific location:
• Design the vessel and structures on the deck against the predicted green water impact load levels.
• Optimise the bow shape (underwater shape and above water bow flare).
• Increase the freeboard height such that green water is prevented completely.
• Increase the freeboard height such that the green water loads are reduced to acceptable levels and design for these load levels.
• Optimise the structures on the deck to minimise the green water impact loads.
• Use protecting breakwaters in front of critical structures on the deck.
All these options have their advantages and disadvantages. The semi-empirical design evaluation method and the different design options are discussed in a case study, focussing on a new DP FPSO concept.