Raymarine evolution systems accommodate hydraulic, mechanical and power assisted stern drive systems. The Drive unit is the part that interfaces with your vessel’s steering system to keep you on the right course. Raymarine has a broad range of drive units to match almost any type of steering system. Raymarine Evolution pilots connect to hydraulic steering systems using a rugged hydraulic pump matched to the capacity of the hydraulic steering system. If your system is hydraulic You’ll need to find out the size (in cc) of the hydraulic cylinder ram(s) mounted to the rudder or inboard engined boats, or to the drive unit on outboard engined boats. Your steering system documentation will have this information.