A life raft and a person in the water go overboard at the Wandelaar pilot station off Zeebrugge. Where do they drift, and where should the search look? We let OpenDrift Leeway, the search and rescue drift model of the Norwegian Meteorological Institute, follow 1,000 possible drifts of each, with the real currents and winds of two days in November 2007. On a calm day, Wednesday 14 November 2007, the wind is light and the tide does the work. Every six hours the drift turns, and the cloud slowly creeps south-west along the coast towards De Haan and Ostend. After two days most of the drifts are still at sea, and the search area has grown to about 120 square kilometres for the raft and about 290 for the person in the water. On a stormy night, Friday 9 November 2007, a north-westerly gale of about 30 knots blows. The life raft catches the wind and is driven onto the Zeebrugge breakwaters within a few hours. A person in the water lies low in the water, drifts slower and spreads far wider, from Ostend to Cadzand. The two objects behave differently because the wind pushes a raft with a canopy much harder than a person who floats almost entirely below the surface. That is why search and rescue planners compute a separate search area for each. This is a model. The currents come from a 7 km ocean model with tides, the winds from satellites at 0.25°, and the drift coefficients from field experiments with real rafts and dummies.
Source: Drift model: OpenDrift Leeway (MET Norway). Life raft with deep ballast and canopy (4 to 14 persons); person in water (mean values). Currents: E.U. Copernicus Marine Service, North-West Shelf reanalysis (NWSHELF_MULTIYEAR_PHY_004_009), hourly at 7 km. Winds: Copernicus satellite winds (WIND_GLO_PHY_L4_MY_012_006), hourly at 0.25°. Coastline: GSHHG. Visualisation by The Moving Sea
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