Type 3 Hydraulic Linear – 12V. Type 3 Hydraulic Linear system for mechanically steered vessels up to 77,000lb (35,000kg) displacement.. 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:. Features: Hydraulic ram: a self-contained autopilot steering cylinder 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.