Rudder system, comprising: a foldable rudder part, - a rudder housing on which the foldable rudder part is rotatably mounted, - a first resilient element which is mounted on an axle fixed to the rudder housing, a spring force of the first resilient element urging the foldable rudder part into the folded-out position, - a resilient locking device, - the foldable rudder part being movable from a folded-in position into a folded-out position relative to the rudder housing, - the resilient locking device being held in a biased position by the foldable rudder part when the foldable rudder part is located in the folded-in position, - the resilient locking device is transferrable from the biased position by detensioning into an at least partially detensioned position when the foldable rudder part is located in the folded-out position, and - the resilient locking device blocking a movement of the foldable rudder part relative to the rudder housing in the at least partially detensioned position, characterised in that - the resilient locking device comprises a resilient element formed as a leg spring, the resilient locking device having a movable first leg and a second leg which is fixed at least in part to the rudder housing. a foldable rudder part, - a rudder housing on which the foldable rudder part is rotatably mounted, - a first resilient element which is mounted on an axle fixed to the rudder housing, a spring force of the first resilient element urging the foldable rudder part into the folded-out position, - a resilient locking device, - the foldable rudder part being movable from a folded-in position into a folded-out position relative to the rudder housing, - the resilient locking device being held in a biased position by the foldable rudder part when the foldable rudder part is located in the folded-in position, - the resilient locking device is transferrable from the biased position by detensioning into an at least partially detensioned position when the foldable rudder part is located in the folded-out position, and - the resilient locking device blocking a movement of the foldable rudder part relative to the rudder housing in the at least partially detensioned position, - a rudder housing on which the foldable rudder part is rotatably mounted, - a first resilient element which is mounted on an axle fixed to the rudder housing, a spring force of the first resilient element urging the foldable rudder part into the folded-out position, - a resilient locking device, - the foldable rudder part being movable from a folded-in position into a folded-out position relative to the rudder housing, - the resilient locking device being held in a biased position by the foldable rudder part when the foldable rudder part is located in the folded-in position, - the resilient locking device is transferrable from the biased position by detensioning into an at least partially detensioned position when the foldable rudder part is located in the folded-out position, and - the resilient locking device blocking a movement of the foldable rudder part relative to the rudder housing in the at least partially detensioned position, characterised in that - the resilient locking device comprises a resilient element formed as a leg spring, the resilient locking device having a movable first leg and a second leg which is fixed at least in part to the rudder housing. - the resilient locking device comprises a resilient element formed as a leg spring, the resilient locking device having a movable first leg and a second leg which is fixed at least in part to the rudder housing.