Green Water On Norwegian Production Ships Available to Purchase

Green water events have made local damage on Norwegian production ships in sea states significantly lower than the 100-year sea states. These incidents have occurred both in the bow area, amidships and aft. Both analyses and model testing demonstrate a significant amount of green water on the deck structures in the 100-year wave situations. There is no general agreement on how to calculate the waves entering the deck of the ship, nor how well the wave height and the freeboard exeeedance are correlated. The model tests show a large scatter when relating green water wave height and the corresponding freeboard exceedance. Significant modifications have been made on the production ships, such as raised forecastle and installation of wave-breaking walls. Operational restrictions have also been introduced, including restrictions to personnel access in green water zones and storage limitations. This paper describes the Norwegian requirements to air gap and green water. A description of the five production ships in Norway and the green water incidents are included. The status of the methods for evaluating the green water phenomenon as well as precautions taken to prevent further incidents, are also described. INTRODUCTION This paper presents some considerations related to green water on production ships as seen from the Norwegian Petroleum Directorate. The data and analyses presented in this paper is collected by the Norwegian Petroleum Directorate from the work performed by the operators of production ships Statoil, Saga (Hydro) and Esso. Green water is defined as the solid water which is coming on the deck of a ship in large waves. Compared to white water, which is a mixture of air and water (foam or spray), green water refers to a more compact mass of water, often in the form of a water washing along and across the deck (Standing 1997).