Deck wetness

Deck wetness is the shipping of green water over the bow or deck edge, counted as the frequency of events in which the relative motion between the wave surface and the freeboard exceeds the available freeboard at a chosen station. It is predicted from the relative-motion response and its spectrum: assuming a Rayleigh distribution, the rate of exceedance per hour is the zero-crossing frequency times exp of minus freeboard squared over twice the relative-motion variance. High deck-wetness rates drive green-water loads on deck fittings and hatch covers and set seakeeping operability limits, typically a criterion of about 30 occurrences per hour at the forward perpendicular.