Marine propulsion – Jet drive – Having means to increase fluid drive means efficiency
Reexamination Certificate
1999-08-16
2001-02-27
Morano, S. Joseph (Department: 3617)
Marine propulsion
Jet drive
Having means to increase fluid drive means efficiency
C440S040000
Reexamination Certificate
active
06193571
ABSTRACT:
BACKGROUND OF THE INVENTION
Waterjet propulsors have been available for many years. Some of their obvious advantages over propellers include that they have no exposed rotor, have low underwater noise signature, offer even engine loading, and offer shallow draft. However, the waterjet's efficiency falls far short of the efficiency of an underwater propeller at low boat speeds. The propulsive coefficient of a typical underwater propeller at 16 knots is about 65 percent while that of a waterjet at the same 16 knots would be only about 40 percent. Those numbers given an advantage to the underwater propeller of 38 percent at that 16 knot speed. The waterjet becomes more competitive at higher speeds where the drag of the underwater propeller's appendages including shaft, strut, rudder, etc. causes it to have a severe disadvantage. The competition to the waterjet then becomes the surface propeller that, in its normal design, operates aft of the transom or a step in the boat's bottom. Only the lower half of the surface propeller is in the water. As such the surface propeller avoids shaft, thrust, and, in some designs, rudder drag. While generally considered to be rather inefficient at low boat speeds, the surface propeller is considered the favored propulsor at very high boat speeds.
The Kort Nozzle, first introduced in the 1930's, yields even greater performance for a variation of the propeller at low boat speeds. It applies a simple ringed nozzle around the periphery of an underwater propeller. By use of carefully designed angled airfoil shapes to the nozzle ring it is possible for the Kort nozzle to actually gain thrust from external forces acting on the nozzle. A well designed Kort nozzle shows noticeable performance gains over a standard underwater propeller at speeds up to, say, 16-20 knots. Beyond those speeds, the drag of the nozzle itself rules out use of the Kort nozzles. As such, Kort nozzles are widely applied to tug boats and other low speed mostly work boats. For purposes of this application, low speed is defined as boat speeds up to and including 20 knots and high speed as boat speeds of over 20 knots.
In summary, the waterjet propulsor is severely outclassed from efficiency standpoints at low to moderate, up to about 25 knot, and very high, over 60 knot, speeds. The reason for much of its efficiency shortcomings has to do with its inlet performance. A well-designed waterjet pump can have a rotor efficiency of 93 percent, flow straightening stator vane efficiency of 92 percent, and discharge nozzle efficiency of 98 percent. That comes to an overall pump efficiency of 84 percent. However, its averaged inlet pressure recovery efficiency will probably only be in the 70 percent area. Consequently, the best overall efficiency that can be expected from such a waterjet propulsor while running at its best performance at hihg boat speeds is about 59 percent. The major reason that waterjet inlet efficiency or inlet pressure recovery is so poor is because of distortion in the inlet flow. The high velocity incoming water in a typical flush with the hull waterjet inlet piles up over the lower half of the inlet duct. Due to this distorted flow, the rotor generally sees recoveries of 90 percent or more of boat freestream dynamic head over its lower half and as low as 50-60 percent over its upper half.
The instant invention offers greatly improved thrust values for the waterjet at all boat speeds. In its preferred embodiment, it decreases the amount of flow distortion that the rotor sees as well as gains thrust advantage from an airfoil shaped flow deflector strategically placed in the inlet duct. Further, generally airfoil shaping of the lower outside portion of the inlet housing so that such housing is submerged adds to thrust with little or no increase in external drag.
In addition to the significant performance gains in waterjet performance to be realized by the instant invention, a significant advantage in the form of a discharge jet-trimming device is also offered. These features are described in detail in the following sections.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is the principal object of the preferred embodiment of the instant invention to provide a new waterjet propulsor that offers efficiencies competitive with or superior to the propeller at all boat speeds.
It is a related object of the invention that thrust enhancements shall be provided by specific arrangement and angling of the underside of the inlet of the waterjet.
It is a further object of the invention that a substantially transversely oriented divider shall be placed upstream of the rotor inlet to aid in directing flow to the rotor to thereby enhance rotor performance.
It is a directly related object of the invention that such a flow divider shall be, at least in part, airfoil shaped.
It is yet a further related object of the invention that such a flow divider shall have forces acting on it that add forward thrust to enhanced waterjet propulsor.
It is a further related object of the invention that said flow divider may be separated into two or more parts so that liquid flow can travel between upper and lower surfaces of the flow divider.
It is another object of the invention that a nozzle that has the ability to control the trim of the waterjet propulsor driven boat be offered.
It is a directly related object of the invention that movable nozzle elements disposed within a fixed nozzle structure can be used to apply trimming forces to the boat.
It is yet another directly related object of the invention that such movable nozzle elements are, at least partially, returned to their neutral positions by force of the water discharging from the nozzle.
It is a further related object of the invention that similar movable nozzle elements to those use for trim can be positioned to accomplish steering of the waterjet propelled boat.
It is yet another object of the invention that a steering rudder can be positioned aft of or at least partially internal to the fixed nozzle to accomplish steering of the boat.
REFERENCES:
patent: 3283737 (1966-11-01), Gongwer
patent: 4050631 (1977-09-01), Syltebo
patent: 5244425 (1993-09-01), Tasaki et al.
patent: 5460553 (1995-10-01), Craig et al.
patent: 5540605 (1996-07-01), Lin
patent: 5879209 (1999-03-01), Jones
Morano S. Joseph
Muldoon Patrick Craig
Van Derwall Robert J.
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