An Octopus Hydraulic Linear Actuator is a simple, effective way to drive the rudder on a boat equipped with a mechanical steering system. The linear actuator is an assembly of an Octopus reversing pump and a marine hydraulic cylinder. This assembly is mounted on the rudder tiller-arm or quadrant. When the autopilot is not in use the cylinder runs freely along with the rudder. When the automatic pilot is in use a solenoid valve on the actuator closes and locks the cylinder. Steering signals from the pilot are now fed to the D.C. motor, which drives the pump to move the cylinder back and forth. De-energized, the solenoid valve immediately disconnects the automatic pilot from the rudder. The actuator has a small translucent oil reservoir, making it easy to check fluid levels. These actuators have only five moving parts. Mechanical simplicity gives our product reliability and ease of service when compared to complicated gear and screw actuators, making our units a favorite for offshore mariners. These actuators are shipped from our factory completely filled with oil and require no additional plumbing.