Advance HCD1000 Marine Gearbox The Advance 800-1000 series marine gearbox has the functions of reverse, forward, clutch, deceleration, and withstand propeller thrust. The HCD800/ HC1000/ HCD1000 gearbox has a vertical off-center primary transmission structure, the HCT800/ HCT800/1/ HCT800/2/ HCT800/3 gearbox has a vertical off-center secondary transmission structure, and the HCT800/2A …