A three-hulled oil combatting vessel (500) has a separating structure (100), which pushes ice blocks (J1), which move between the middle hull (SH1) and side hulls (SH2, SH3) from the prow to the stern, underneath the water surface (WL1). The separating structure (100) may be a grate in the longitudinal direction of the vessel (500). The density of the oil (B4) or oil refining product to be collected is smaller than that of the water, so the oil (B3), which has been separated from the ice blocks (J1) that were pushed down, tends to rise through the separating structure (100) to the water surface. The separating structure (100) separates the oil (B3) from the ice blocks (J1) for easier collection into a container. The separated (B4) oil can thus be collected from the relatively ice-free water surface (WL1) with an oil collecting device (200), which may have a brush skimmer.