Method for producing a thrust in manoeuvering engines for a watercraft and a manoeuvering engine constructed for the same

Method of producing thrust in manoeuvering engines for watercraft in which, according to the drag jet principle, driving water and suction water are supplied to a front engine part and a following rear engine part of the engine, and characterized by the steps of subdividing the suction water into a first and a second flow portion, introducing the first flow portion as a suction water jet into an inlet port at one end of an axially elongated chamber within the front engine part and flowing the first flow portion to an outlet port spaced axially from the inlet port through a passage within the chamber having an increasing cross-sectional area toward the outlet port, forming the rear engine part as an axially extending diffuser nozzle in axial alignment with and extending axially outwardly from the outlet port of the chamber forming the front engine part with the inner surface of the rear engine part diverging in the direction outwardly away from the outlet port of the front engine part, overlapping the rear engine part over the outlet from the front engine part and forming an annular passageway therebetween supplying driving water into an annular duct laterally enclosing the first flow portion of the suction water through the front engine part, introducing an annular driving water jet from the annular duct into the inlet end of the diffuser nozzle laterally enveloping the first flow portion exiting from the outlet of the chamber so that the annular driving water jet laterally surrounds the first flow portion exiting from the outlet port of the front engine part and flows outwardly toward the inside wall of the rear engine part, introducing the second flow part of the suction water in the form of an annular jet laterally enclosing the annular jet of the driving water at the inlet end of the diffuser nozzle and flowing the first flow portion and second flow portion of the suction water through the diffuser nozzle with the annular driving water jet located therebetween so that the annular jet of the second flow part spaces the annular jet of driving water from the inside wall of the rear engine part whereby frictional losses of the driving water annular jet are avoided along the inner wall of the rear engine part.

Mamoeuvering engine for watercraft operated in accordance with the drag jet principle, comprising an axially extending engine comprising a front engine part and a rear engine part, said front engine part comprising an axially extending suction duct, said suction duct being laterally defined by an annular wall forming an annular duct encircling said suction duct, said suction duct having an inlet end and an outlet end and having an increasing diameter in the direction of the outlet at least in the region of the outlet end, said annular duct having an annular slot at the outlet end of said suction duct through which driving water exits therefrom with said annular slot encircling the outlet end of said suction duct and being shaped to direct flow angularly outwardly relative to the axis of said suction duct, said rear engine part comprises a diffuser nozzle encircling and extending axially from the outlet end of said suction duct, said diffuser nozzle overlapping the outlet end of said suction duct and having an inlet port at the end thereof encircling the outlet port of said suction duct and an outlet port at the opposite end thereof spaced outwardly from said suction duct, said inlet port of said diffuser nozzle being annular and having a smaller maximum diameter than the diameter of the outlet port of said diffuser nozzle and said inlet port of said diffuser nozzle having a minimum diameter greater than the maximum diameter of said outlet port of said suction duct, said inlet port of said diffuser nozzle laterally encircling said outlet port of said suction duct and forming an annular intake slot between the outer surface of said annular duct and the inner surface of said diffuser nozzle at said inlet port thereof whereby said annular intake slot laterally encircles said annular discharge slot from said annular duct so that a suction water jet can flow into said diffuser nozzle through said annular intake slot laterally bounding the outer surface of the annular flow of driving water from said discharge slot from said annular duct so that the suction water jet spaces the annular flow of driving water from the inside surface of said diffuser nozzle whereby frictional losses of the driving water are worked along the inside surface of said diffuser nozzle.