Abstract: A boating propeller for controlling the discharge of engine exhaust gases from the central hub of a boating motor unit by making provision for confining said gases to the inner most fraction of the structure (that within the shroud) and discharging it downstream of the propeller when operating the unit in either the forward or astern mode of operation.

Abstract: A propeller for controlling the discharge of gases and cooling water exhausting from the central hub of an outboard motor unit comprising a cylindrical shroud surrounding the propeller hub to confine the exhaust to the inner most part of the blades and discharge it downstream of the propeller when operating the unit in the forward or reverse mode. Several attachments to this shroud which enhance the discharge performance of the propeller are disclosed. An alternate embodiment comprises a shroud which may be attached to a conventional through-hub marine propulsion device to channel the exhaust away from the propeller area.