US Patent 9266594 Use of center engine for docking

In a marine propulsion control system for controlling a set of propulsion units carried by a hull of a vessel, cavitation typically occurs on the propulsion unit with reverse gear engaged, and in a triple propulsion unit installation the normally idle center propulsion unit can be used to increase the reverse thrust and thereby limit the RPM of propulsion units in reverse, so that the cavitation effect is limited, and simultaneously allow for higher forward thrust on the third propulsion unit, thus increasing the total thrust for the vessel.