Abstract: A jet propelled boat whose propulsion unit is very compact vertically and in which entrance of the water into the exhaust system is effectively prevented. The jet propulsion unit includes an engine having a vertical output shaft, an impeller housing secured to the engine beneath the same and housing an impeller driven by the engine, and an exhaust gas housing surrounding the impeller housing having the walls thereof spaced from the impeller housing sufficiently to form a gas chamber, this exhaust gas housing being connected to the exhaust gas discharge below the normal water line and also to the exhaust manifold. The propulsion unit may be used either in connection with an inboard engine or with an outboard engine. In either case, provision is made for changing the direction of the boat and for reversing the same.

Abstract: A power operated surfboard which has a raised rear hollow portion at the rear in which is disposed an impeller housing having an impeller therein and a water discharge passage extending rearwardly from the housing. An internal combustion engine is supported above the impeller housing and has a short vertical axis connected to the impeller which rotates about a vertical axis. Surrounding the impeller housing is an exhaust gas housing which communicates with the exhaust gas passage of the engine and with a discharge chamber beneath the floor of the surfboard. The exhaust gas housing is gas tight and provides a gas cushion which retards the entrance of water through the discharge chamber into the exhaust passage of the engine, when the surfboard is not being operated. This is aided by a flexible valve disposed at the discharge outlet of the discharge chamber to retard the entrance of water into the discharge chamber.