Abstract:
A water-jet drive mechanism for driving of watercraft and including an elbow located in the hull of the watercraft and containing a pump or the like by which water is sucked in at the bottom of the watercraft through a suction passage and is ejected downwardly through an ejector passage. A gas is supplied to the water jet at the ejector passage.

Description:
FIELD OF THE INVENTION 
     The invention relates to a water-jet drive mechanism, for driving of watercraft and of the type including an elbow located in the hull of the watercraft and containing a pump by which water is sucked in at the bottom of the watercraft through a suction passage and is ejected downward through an ejector passage. 
     BACKGROUND OF THE INVENTION 
     Water-jet drive mechanisms of this type are known. They serve to drive or to drive and control ships. In the latter case, it is possible for the above-mentioned elbow to be pivotable about a substantially vertical axis. The pivot axis of the elbow and the axis of rotation of the pump may thereby be located coaxially or eccentrically to one another. The pump axis can also be installed inclined. (U.S. Pat. No. 3,098,464, German OS No. 2 757 454). 
     In the drive mechanisms of the mentioned and similar type, the water jet applies itself to (in effect sticks to) the bottom surface of the ship behind the elbow or pump and thereby entrains large amounts of water from the surroundings. This results in a loss of the thrust and a lowering of the boat. 
     The basic purpose of the invention is to avoid this disadvantage, namely to take care that the jet comes free better from the ship and thus carries out no or at least almost no damaging action. 
     The basic purpose of the invention is attained with a water-jet drive mechanism, wherein a gas is supplied to the water jet at the ejector passage. It is thereby particularly advantageous to develop the invention so as to provide a passageway which connects the ejector passage to the outside air and supplies such gas to the water jet. This construction of the invention has namely the advantage that, in the case of pivotable elbows, the air-supply output pivots with the ejector passage. This avoids having the air sucked in by the water pump or the like. 
     The invention achieves the following advantages. The ejecting angle of the water jet is maintained which reduces the friction on the hull of the ship; this results in an increase of the thrust. Furthermore it is achieved that water is not entrained from the surroundings. This results in a lesser lowering of the ship and a smaller wave formation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is discussed in connection with FIGS. 1 to 3. 
     FIG. 1 schematically illustrates a watercraft with a jet and contrasts the condition of the jet with the invention respectively absent from, and applied to, the watercraft. 
     FIG. 2 is a schematic cross-sectional view of a water-jet drive mechanism according to the invention. 
     FIG. 3 also is a schematic cross-sectional view of a different exemplary embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically illustrates a watercraft 1 with a water-jet drive mechanism 2. Same consists substantially of an elbow 3, in which a propeller pump 4 is supported. The propeller pump is driven by a motor 5 through drive elements which will be described below. The elbow is pivotable about a pivot axis 6 and is supported drivably therefor. The propeller shaft which carries the propeller of the propeller pump 4 is inclined to the pivot axis. The ejector passage 7 of the elbow is directed inclined downwardly. The watercraft is driven by the ejected water jet and is controlled by pivoting the elbow. However, in the absence of the invention, the water jet is not angled downwardly, but instead the direction of the jet, as indicated at 8, lies along the hull of the ship, which results in the above-described disadvantages. With the invention, which is described in greater detail hereafter in connection with FIGS. 2 and 3, the water jet is directed at a downward inclination, as indicated at 9. 
     The water-jet drive mechanism will be referred to hereinafter more briefly as the drive mechanism. 
     FIG. 2 illustrates a drive mechanism, in which the propeller pump 10 is arranged, in contrast to FIG. 1, parallel to but eccentrically of the pivot axis 6 of the elbow 3. The propeller pump is driven by the motor 5 through a drive shaft 11, a bevel gear set 12, a spur gear set 13 and a propeller shaft 14, on which the propeller of the propeller pump 10 is mounted. The invention is also usable for embodiments in which the propeller shaft is supported axially with respect to the pivot axis 6. The elbow 3 is pivotally housed within a recess defined by a housing 20 fixed within the watercraft 1. The elbow 3 can be pivoted about the axis 6 by being driven by a second motor 15 (here mounted on the housing 20) through a gear drive 16 or the like. A suitable bearing 17 and seal 18 are provided between the elbow 3 and housing 20. The elements and principles for this are known, and thus parts 15, 16, 17 and 18 are only schematically illustrated. 
     The propeller pump 10 sucks water in through a suction passage 19 and ejects it through the ejector passage 7 in a desired direction depending on the position of the elbow. In the absence of the invention, the jet flows along the surface of the hull of the ship, as shown at 8 in FIG. 1. To prevent this, an inlet opening 21 is provided in the housing 20 and at least one opening 22 is provided in the elbow. The openings 21 and 22 form at least one passageway through which air can pass from outside the housing 20 into the ejector passage 7. A gap 23 between the housing and the elbow acts as an annular groove, which insures that in every position of the elbow air can pass serially through the openings 21 and 22. 
     The gap 23 is sealed from the outside on the one side by the water and on the other side by the seal 18. If necessary, several inlet openings, an additional annular groove and additional seals can be provided. 
     The described air supply takes care that the water jet does not lie against the hull of the ship, but indeed exits at a downward inclination, as at 9 in FIG. 1. 
     The exemplary embodiment according to FIG. 3 differs from the one according to FIG. 2 in that the pump shaft 25, on which the impeller of a centrifugal pump 24 is mounted, is supported so as to be inclined to the swivel axis 6. The torque is transmitted through a cardan shaft 26. In place of the cardan shaft, a suitable gear drive, for example a bevel gear set, can be provided. 
     The FIG. 3 embodiment differs further from that of FIG. 2 in that the inlet opening 27 is provided higher in the housing, so that the air enters an annular chamber 28, which is provided above the elbow 29. From here an opening 30 extends into the ejector passage 7. The annular chamber 28 is sealed off like in FIG. 2. The air supply here too causes the water jet 9 to exit inclined downwardly. 
     It is also advantageous for several reasons, for example for the noise damping, if the inlet opening, or openings, 21 or 27 is, or are, connected to the exhaust passage of the motor 5. &#34;Motor&#34; in the sense of the invention is any power engine which serves the drive, for example an internal combustion engine, a gas or steam turbine or a steam engine. 
     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.