The invention provides an object (10), that during use is at least partly submerged in water, wherein the object (100) is selected from the group consisting of a vessel (1) and an infrastructural object (15), the object (10) further comprising an anti-biofouling system (200) comprising an UV emitting element (210), wherein the UV emitting element (210) is configured to irradiate with UV radiation (221) during an irradiation stage one or more of (i) a first part (111) of an external surface (11) of said object (10) and (ii) water adjacent to said first part (111) of said external surface (11) of said object (10), wherein the object (10) further comprises protruding elements (100) with the UV emitting element (210) configured between the protruding elements (100) and configured depressed relative to the protruding elements (100).