A method for installing an offshore jack-up structure having a buoyant platform to be towed and a plurality of legs, the method comprising the steps of:(a) providing a pair of ultrasonic transmitter-receivers on a longitudinal and horizontal center line of the platform,(b) providing of ultrasonic transmitters on a longitudinal and horizontal center line of a target structure to which the rig is approached; and(c) receiving signals transmitted from the ultrasonic transmitters of the target structure by the ultrasonic transmitter-receivers of the platform to determine a relative distance between the rig and the target structure.