Disclosed herein is a hydraulic control unit for a marine installation comprising a helm station including a pump comprising first and second pump discharge ports, which pump is selectively and alternatively operable to deliver fluid under pressure from the first and second pump discharge ports, a plurality of steerable marine propulsion units, a plurality of corresponding hydraulic steering cylinders respectively connected to each of the propulsion units and including respective first ports which, when subject to fluid under pressure, tend to steer the propulsion units in one direction and including respective second ports which, when subject to fluid under pressure, tend to steer the propulsion units in the opposite direction, and a hydraulic tie line connecting the second port of each steering cylinder except the last steering cylinder with the first port of the following steering cylinder, which hydraulic control unit includes a hydraulic circuit adapted for communication between the first pump discharge port and the first steering cylinder first port and between the second pump discharge port and the last steering cylinder second port and with a tie line and operable, during the presence of fluid under pressure at one of the first and second discharge ports, and in response to the absence of fluid under pressure in the tie line, for preventing steering movement of the other of the first and last propulsion units, and operable, when the steerable propulsion units are in nonangularly aligned steering positions, for locating the steerable propulsion units in angularly aligned positions.