Mercury - Stern Thruster Top Assembly for Pontoon JPO (No Cover) Control System 8M4509077. OverviewThis stern thruster top assembly is part of the Joystick Piloting setup used on single-engine pontoons. It helps the stern make controlled sideways moves, which takes a lot of stress out of docking a wide pontoon in wind or current. This version is the top assembly only, without the cover, and is meant for service or replacement work. Once installed, the stern responds more predictably during slow