A roller bearing system for mounting a turret (5) in a vessel is described, the system comprising an inner ring (7), an outer ring (8) and at least one set of rollers (11,12,13) arranged between the inner and outer rings. The inner and outer rings are provided with raceways (16,17) at the location of the rollers (11,12,13) and at least one of the raceways cooperating with said one set of rollers is movably mounted in a slot (14,15) of the inner or outer ring.