Abstract: A suction device for a jet propeller assembly for a boat comprises a motor actuating a pump assembly and a suction conduit conveying water to the pump assembly. The suction inlet is located aft of the boat stern transom and has a rectangular minimum height cross-section with width to height ratio of 3 to 6. Preferably the suction inlet is located entirely rearwardly of the stern transom, the minimum height cross-section plane makes a 30.degree. to 60.degree. angle with the horizontal and the distance between the forward edge of the suction inlet and the pump inlet cross-section is not greater than twice the inlet cross-section diameter. Thus the suction device can be displaceably mounted with respect to the hull, no opening in the keel of the hull is necessary and the suction conduit can be located entirely aft of the stern transom. The propeller assembly efficiency and the wake dynamics are improved.