Hydraulic Linear Drive Type 3 – 24V. The hydraulic linear drive system is designed for boats with existing mechanical steering systems, not hydraulic steering systems. It provides a totally isolated autopilot steering system consisting of: Hydraulic ram: a self-contained autopilot steeringcylinder with a load limiting system and a built in clutch (to allow friction-free steering when the autopilot is not in use),Reversing hydraulic pump: powers the hydraulic ram,Hydraulic fluid reservoir: supplies hydraulic fluid to the system..