Jet propulsion system for a watercraft

1. A jet propulsion system for a watercraft, comprising:

a duct defining an inlet;

a venturi unit defining part of the duct and defining a venturi outlet;

an impeller housing defining part of the duct and disposed between the inlet and the venturi unit; and

an impeller disposed within the impeller housing, the impeller being rotatable about an impeller rotation axis in (i) a forward direction whereby the impeller propels water out of the venturi outlet, and (ii) a reverse direction whereby the impeller propels water out of the inlet,

the venturi unit comprising:

a venturi conduit having a peripheral wall defining at least one aperture, the venturi conduit defining a venturi inlet and the venturi outlet, the venturi inlet having a greater cross-sectional area than the venturi outlet, wherein:

when the impeller rotates in the forward direction, water flows from the venturi inlet to the venturi outlet, and

when the impeller rotates in the reverse direction, water flows from the venturi outlet to the venturi inlet;

and

at least one door connected to the venturi conduit, the at least one door being movable between a closed position when the impeller rotates in the forward direction, and an open position when the impeller rotates in the reverse direction,

in the closed position, the at least one door closing the at least one aperture, and

in the open position, the at least one door opening the at least one aperture such that water flows into the venturi conduit via the at least one aperture.

2. The jet propulsion system of claim 1 , wherein, in the open position, the at least one door opens the at least one aperture such that water flows into the venturi conduit via the at least one aperture and the venturi outlet.

3. The jet propulsion system of claim 1 , wherein the at least one door includes a plurality of doors.

4. The jet propulsion system of claim 1 , wherein:

each of the at least one door comprises:

a door seat; and

a door member pivotably connected to the door seat;

in the closed position of the at least one door, the door member being shut against the door seat; and

in the open position of the at least one door, the door member being pivoted inwardly such that at least part of the door member is pivoted into the venturi conduit.

5. The jet propulsion system of claim 3 , wherein the plurality of doors comprises no more than four doors.

6. The jet propulsion system of claim 3 , wherein the doors of the plurality of doors are distributed along a bottom half of the venturi conduit.

7. The jet propulsion system of claim 3 , wherein:

the venturi conduit comprises a plurality of vanes extending longitudinally along an inner side of the peripheral wall, the vanes being circumferentially spaced from one another;

each of the doors of the plurality of doors being positioned between two of the vanes.

8. The jet propulsion system of claim 1 , wherein the at least one door is generally triangular.

9. The jet propulsion system of claim 1 , wherein the at least one door is passively actuated between the closed and open positions such that:

when a pressure inside the venturi conduit is less than a pressure outside the venturi conduit, the at least one door assumes the open position; and

when the pressure inside the venturi conduit is greater than the pressure outside the venturi conduit, the at least one door assumes the closed position.

10. The jet propulsion system of claim 1 , further comprising:

a reverse stator disposed between the impeller and the inlet of the duct, the reverse stator being generally annular and comprising a plurality of vanes extending radially within the duct.

11. The jet propulsion system of claim 1 , further comprising:

an intake ramp defining part of the duct and extending from the inlet of the duct to the impeller housing.

12. The jet propulsion system of claim 1 , further comprising:

a drive shaft operatively connected to the impeller to cause rotation of the impeller about the impeller rotation axis, the driveshaft being adapted for connection to a gearbox.

13. The jet propulsion system of claim 1 , further comprising:

a forward stator disposed between the impeller and the venturi unit, the forward stator comprising a plurality of vanes extending radially within the duct.

14. The jet propulsion system of claim 13 , further comprising:

a nose cone mounted to the forward stator and extending into the venturi unit, the at least one door abutting the nose cone in the open position.

15. The jet propulsion system of claim 1 , further comprising a grate adjacent to or in the inlet of the duct.

16. A watercraft, comprising:

a hull having a bow and a stern opposite the bow;

a motor supported by the hull; and

a jet propulsion system, comprising:

a duct defining an inlet in a bottom of the hull;

a venturi unit defining part of the duct and defining a venturi outlet;

an impeller housing defining part of the duct and disposed between the inlet and the venturi unit; and

an impeller disposed within the impeller housing, the impeller being operatively connected to the motor, the impeller being rotatable about an impeller rotation axis in (i) a forward direction whereby the impeller propels water rearwardly, and (ii) a reverse direction whereby the impeller propels water forwardly,

the venturi unit comprising:

a venturi conduit having a peripheral wall defining at least one aperture, the venturi conduit defining a venturi inlet and the venturi outlet, the venturi inlet having a greater cross-sectional area than the venturi outlet, wherein:

when the impeller rotates in the forward direction, water flows from the venturi inlet to the venturi outlet, and

when the impeller rotates in the reverse direction, water flows from the venturi outlet to the venturi inlet;

and

at least one door connected to the venturi conduit, the at least one door being movable between a closed position when the impeller rotates in the forward direction, and an open position when the impeller rotates in the reverse direction,

in the closed position, the at least one door closing the at least one aperture, and

in the open position, the at least one door opening the at least one aperture such that water flows into the venturi conduit via the at least one aperture.