Kinematics of green water in a large data set of events and a resulting prediction method of probability

Abstract

Green water is an extreme event that impacts ships and poses a risk to those on board. Conventional methods of screening assume a direct relation between exceedance and green water. This article demonstrates that the relation is not direct and identifies a difference between green water and exceedance that does not develop into a flow on deck. A proposed prediction method follows from the difference between green water and exceedance identified from analysing a big data set. The big data set is from experiments modelling 1945 full-scale hours and includes 409 green water events and 729 exceedance events which did not become green water. Pitch was identified as an important indicator for green water as green water events consistently occurred with large forward pitch motion, while exceedance also occurred with neutral pitch. A prediction method of probability is proposed that implements separate limits for the motions and wave elevation that occur simultaneously, thus including the phase difference between the motions and wave elevation. The result is a method for the prediction of the occurrence of green water on the deck of a ship with different forward velocities and in different sea states.