Dual Pump Waterjet

Abstract

Two concentrically positioned axial flow pumps are axially aligned on a single shaft. A high flow pump is positioned outwardly of an inner high pressure pump, each of the pumps having independent inlet means. The pumps provide waterjet thrust efficiently at both low watercraft speeds and high watercraft speeds by providing dual waterjet inlet ports, and manipulating the inlet ports to suit the vehicle needs. During low speed, high drag conditions, both pumps receive water through the dual inlet openings, and during high speed, low drag conditions, the first outer high flow pump is shut down by closing off its inlet port, the remaining high pressure pump providing thrust to propel the already accelerated watercraft.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Waterjet propulsion whereby a stream of water is hydraulically pumped outwardly from a nozzle driven by a high flowrate pump is becoming increasingly more popular with watercraft manufacturers. Usually a water inlet port is located upstream of the pump, the inlet port being positioned beneath the water line, thus the water is picked up through the inlet port and directed towards the pump in the inlet duct. The water is then accelerated by the pump out the exhaust outlet port or nozzle thus propelling the watercraft through the water.

2. Description of the Prior Art

There are several examples of hydraulic jet propulsion devices in the prior art. For example, U.S. Pat. No. 1,548,936 describes a means for propelling boats, which includes a steam engine to drive at least a pair of pumps, the pumps being interconnected between an inlet pipe positioned below the water line which draws in water to the pump, the pump accelerates the water to exiting outlet pipes which, in turn, drive the boat forwardly. Additional piping provides a reverse path for the exiting water which causes the ship to reverse direction.

Another waterjet propulsion device is described in U.S. Pat. No. 3,007,305. This patent discloses a constant speed, two-stage axial flow pump inside of an inlet duct being externally driven by an engine. The inlet duct leading to the two-stage flow pump directs water into the pump and out through an outlet exhaust nozzle to propel the vehicle forwardly. Thus both stages "see" the same water inlet flow.

Another U.S. Pat. No. 3,328,061, similar to the one just discussed, discloses a pump inside of a water duct, the two-stage device having a first impeller that is driven at a slower speed than the second downstream impeller, thus providing varying speed, two-stage propulsion. The pump draws water through an inlet opening and outwardly through an exhaust nozzle to propel the craft through the water. The two-stage device, thus, results in a high speed pumping unit with corresponding high pressure rise through the unit. A second U.S. Pat. No. 3,405,526 is issued to the same inventor (Aschauer), and discloses a similar means to propel water through a water duct. This patent describes a more sophisticated means to prevent cavitation between stages, thus effecting a more efficient pumping operation.

All of the aforementioned patents exhibit the same inefficiencies relative to thrust versus drag at various watercraft speeds. A conventional waterjet pump is designed to produce the thrust required to overcome the boat drag at the maximum boat design speed. However, at lower speeds, due to reduced pump power or increased boat loads, the propulsive efficiency is reduced. All of the aforementioned prior art devices are provided with a single water inlet port for the driving pump. Therefore, the pump is less efficient at low speeds and high drag conditions, the pump being designed to reach its maximum efficiency at a certain watercraft velocity drag ratio. Therefore, it follows that the pumps are highly inefficient during low speed, high drag conditions.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide dual pumps on a single shaft having separate inlet ports for each pump.

More specifically, it is an object of this invention to provide concentrically oriented pumps on a single shaft, the outer pump being a high flow pump and the inner pump being a high pressure pump. Each of the pumps have separate inlet ports, one of the inlet ports being closed during high speed operation.

The dual pump waterjet may operate with one or two pumps providing thrust. When two pumps are in operation, the driving engine speed reduces at constant horsepower for a given engine throttle setting. The additional pump results in a higher total flowrate which, with the lower pressure rise, matches the engine power characteristics at a lower speed. Thus the lower pump pressure rise results in a lower jet velocity which gives peak propulsive efficiency at a lesser boat velocity. Hence, more thrust is provided during low speed, high drag watercraft conditions. The combination of increased flowrate with a lower jet velocity increases static and low speed jet thrust. As the watercraft speed increases with both pumps in operation on a single shaft, the boat characteristic changes as the velocity increases. As the drag is overcome by the dual pump operation, the high flow pump is shut down by way of closing the water inlet duct feeding the high flow pump. Since both of the pumps are on a single shaft, the high flow pump surrounding the internal high pressure pump then offers no resistance since it is no longer in contact with the inlet water flow from its separate inlet duct. The dual pump waterjet then provides increased thrust capability in the high drag, low speed region and permits higher speeds under reduced power settings. Once the high drag region is overcome, full power is available to drive the single high pressure pump to provide a high velocity waterjet which is more efficient in high craft speed regions. Conventional waterjet craft having single or dual pumps with a single inlet require additional horsepower to accelerate the watercraft beyond the high drag, low speed region because of the inefficiency of the single inlet, single pump operation.

An advantage over the prior art is evident in that the dual pump, with both inlet ports for each pump open, provides high flow with lower jet velocity which increases static and low speed thrust capability during high drag, low speed watercraft conditions. When the high flow inlet port leading to the high flow pump is closed, the high pressure pump takes over during high speed operations to maintain the craft in the high speed, low drag range. In this region, the inlet drag is reduced by closing the high flow inlet.

Another advantage over the prior art is realized in that, with the dual pump operation having separate inlet ports, a lesser horsepower engine is thus required due to the increased efficiency of the thrust capabilities of the pumps.

Still another advantage over the prior art is the ability to accelerate a watercraft in rough water conditions whereby the drag to velocity ratio is much higher. The advantage lies in the increased efficiency of the dual inlet, dual pump waterjet, whereby the increased flowrate of the two pumps in operation is superior to the single inlet, single pump operation of conventional waterjet units in rough water.

The above noted objects and advantages of the present invention will be more fully understood upon a study of the following detailed description in conjunction with the detailed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of a watercraft with a dual pump, dual inlet waterjet device positioned therein;

FIG. 2 is a cross-sectional view of another embodiment illustrating a portion of a watercraft wherein the propulsion unit is mounted externally of the craft;

FIG. 3 is a view taken along lines 3--3 of FIG. 2 showing the dual inlet configuration;

FIG. 4 is a chart illustrating propulsive efficiency percent during one pump and two pump maximum power settings for a hydrofoil boat;

FIG. 5 is a chart illustrating thrust or drag pounds versus hydrofoil craft speed feet per second at various power settings; and

FIG. 6 is a chart illustrating thrust or drag pounds versus conventional chart speed feet per second at various power settings during one pump and dual pump operations.

Referring now to FIG. 1, the waterjet pump generally designated as 10 is mounted within a watercraft 11 normally adjacent the stern or transom 15. The waterjet pump comprises a pump housing 12 having a dual nozzle housing 13 attached thereto. Upstream of the dual nozzle housing 13 is an inlet ducting housing 14 which terminates in a pair of inlet openings flush with the bottom of the watercraft 11. The inlet ducting 14 comprises a highflow inlet duct 16 which directs water towards an inlet torus or manifold 17 which subsequently directs water into the pump generally designated as 35. A separate high pressure inlet duct directs water through opening 19 into the high pressure pump generally designated as 33. The water being directed to torus 17 is influenced by flow straightener 26 immediately before it impacts the high flow impeller blades 38. Similarly the high pressure water flow entering inlet 19 of high pressure duct 18 is influenced by a flow straightener 24 immediately before it impacts the high pressure pump impeller blades 36.

The power shaft 28 is mechanically connected to a source of power (not shown) through coupling 30. Bearings 32 support the end of a drive shaft 34 which leads into the interior of the high pressure inlet duct 18. The drive shaft 34 terminats in a drive shaft support housing 40 which contains a set of bearings 42. Immediately upstream of support housing 40 is a first high pressure pump 33 rigidly affixed to shaft 34. A shroud 37 connected to the outer tips of the impeller blades 36 separates the high pressure pump 33 from the high flow pump 35 attached to the outer surface of shroud 37. The concentric pumps 33 and 35 thus provide two seprate means of propulsion. The drive shaft support housing 40 is rigidly affixed by a multiplicity of support webs and flow straighteners 41 which effect the accelerated flow of water from the plurality of pitched impeller blades 36 and 38. The support webs 41 serve to position the outer high flow nozzle 46 with respect to the inner high pressure nozzle 44 so as to maintain the pair of nozzles concentrically one within the other.

A mechanically actuatable door 22 is affixed to the bottom of the hull 11 and is adapted to be moved into and out of engagement with opening 20 which leads into the high water flow torus 17 and directs the water through the high flow pump 35. It can readily be seen then that when the door 22 is moved into blocking position in opening 20, the water entering duct 16 is arrested thus enabling the high flow impeller blades 38 to free-wheel within the high flow passages 16. When this occurs, the high pressure pump 33 is accelerated with a given power setting, thus causing an increased pressure rise within the high pressure pump 33, thereby accelerating the water out of nozzle 44.

The means by which the door 22 is moved into and out of engagement with opening 20 may be an arrangement of Venetian blinds or slats as seen in FIG. 3 or the other may be hydraulically actuated into and out of engagement with opening 20 or hydrodynamic forces may be utilized to induce the door 22 into and out of engagement with the opening based on the speed of the watercraft through the water. The trap door 22 may be closed manually or, alternatively, hydraulic actuation using the pressure from the pumps may be utilized to actuate the door.

Turning now to FIG. 2, another embodiment illustrates the waterjet pump 10 mounted externally of the watercraft on a transom 15. For example, the dual pumps may be connected to an outboard engine (not shown). The pump housing 80 has a pair of rearwardly directed outlet nozzles 82 and 84 connected thereto. Adjacent the bottom of housing 80 is a high flow inlet duct 86 leading into a high flow inlet torus 88 in housing 80 that is in flow communication with the high flow nozzle 82. At the bottom end of inlet 86 is an inlet opening 90. A second inlet 92 leads into torus 94 in housing 80 which is in flow communication with the high pressure nozzle 84. Inlet 92 has an independent opening 96 positioned within opening 90 to direct water into the high pressure pump.

A pair of concentric pumps 98 and 100 are fixed to a drive shaft 102. The drive shaft is supported within housing 80 by bearing 104, the bearing having a seal 106 adjacent thereto. The end of the drive shaft 102 supports a plurality of pitched high pressure impeller blades 108. At the end of blades 108 is a fixed annular shroud 110 that supports a plurality of pitched high flow impeller blades 112.

The opening 90 may have a series of actuatable slats 114, as viewed in FIG. 3. The slats are actuatably closed by rotating control rod 116 mechanically linked to each of the slats 114, thus closing off opening 90 leading through pump 98, thereby shutting down the high flow pumping operation as heretofore described. A pair of skegs 118 serve to prevent the entering water in openings 90 and 96 from spilling away from the openings during single or dual pump operations.

FIG. 4 is a chart indicating propulsion efficiency at both one-pump maximum power operation and two-pump maximum power operation. Curve 39 indicates a two-pump operation and clearly shows the increased thrust available at the low watercraft speed range while curve 43 indicates a one-pump maximum power operation with the trap door or slats closing off the high flow water to the high flow pump, thus indicating the thrust available at higher watercraft speeds. It can be seen that the one-pump maximum power operation is more efficient at the high speed ranges while it is much less efficient at the low speed, high drag region, as indicated by the curve. Therefore, to gain maximum efficiency of the watercraft power available, the two-pump operation indicated by curve 39 is used in the high drag, low speed ranges to provide maximum thrust up to a certain watercraft speed, whereupon the inlet to the high flow pump is closed, thus enabling the one-pump operation to take over, thereby providing increased speeds at the low drag speed range indicated by the longer curve 43.

Turning to FIG. 5, a 32-foot hydrofoil boat is used as an example which has a 344 maximum horsepower engine installed therein. The chart indicates the performance of the hydrofoil boat at certain drag conditions at specific speeds. The boat operates during the high-drag region A (curves 52 and 56) with the boat hull supporting the weight by buoyancy. Region B is a transition region during which time the hydrofoils provide a substantial lift. In region C the hull is lifted free of the water by the hydrfoil lift devices. The boat drag is increased as the height of the waves in the water are increased (indicated as curves 52 and 56). At maximum engine power (344 horsepower) single pump operation provides maximum boat speed capability at both zero and maximum wave height drag. However, with a power setting of 170 horsepower (bold curves 48 and 49) or a similar engine of 170 maximum horsepower, the single pump will marginally overcome the high hump drag point 50 (intersection of curves 48 and 52) in region B for zero wave height depicted by curve 52 but will not overcome the drag 54 at maximum wave height depicted by curve 56. With one pump in operation at 170 horsepower maximum boat speed capability is 62 ft/sec (intersection 58 of curves 49 and 52) at zero wave height (curve 52) and 22 ft/sec (intersection 60 of curves 49 and 56 at maximum wave height (curve 56). With two pumps in operation the thrust is adequate to insure overcoming phase B maximum drag at both zero and maximum wave heights. At zero wave height, the maximum speed is 44 ft/sec (intersection 62 of curves 48 and 52) and at maximum wave height the maximum craft speed is 33 ft/sec (intersection 64 of curves 48 and 56). Thus it can be seen that the dual pump waterjet provides increased thrust capability in the high drag low-speed region (region B) and may permit higher speeds under reduced power under heavy sea conditions, as shown by the 94 horsepower curves. The dual pump may also be used to permit use of lower installed power than for a single waterjet for reduced installation costs. Dual pump operation also provides high zero and low speed thrust for freeing boats from sandbars, towing, and the like.

FIG. 6 is a chart which uses as an example a 32 foot conventional hull boat having a dual pump waterjet installed therein. In this chart, as in the last chart, the maximum engine power is 344 horsepower and a 94 horsepower throttle setting is indicated by the curves and dotted line. Thrust values are presented for single and dual pump operation. Three boat drag levels are presented by curves 66, 68 and 70. Such drag curves occur when workboats operate with widely varying loads. Dual pump operation permits superior speed (33 ft/sec) which is indicated by the intersection 72 of curves 74 and 66 at maximum drag compared with (25 ft/sec) that is indicated by the intersection 78 of curves 76 and 66, when utilizing a single pump at the same power setting. Single pump operation (curve 76) permits higher speed at the lower drag level as heretofore described. The higher speed may be achieved with the dual pump at the lower drag levels by closing the inlet to the high flow pump which is specifically designed for the lower speed high-drag operations. At reduced power levels (94 horsepower) and speeds, dual pump operation provides maximum boat speed at all drag levels.

Obviously, other configurations may be utilized, for example, two separate pumps being driven by a single power output having dual shafts, the one pump being designed for low speed high drag conditions while the other pump being designed for high speed high pressure conditions, the two pumps being operated so as to shut-down the high flow pump after the high drag region is overcome, thus allowing the high pressure pump to take over.

Claims

We claim:

1. A dual pump waterjet for watercraft comprising:

a first pump means positioned within a first conduit means,

first water inlet means connected to said first conduit means to direct water into said first pump means,

a first nozzle means at the end of said first conduit means to direct water out of said first pump means,

a second pump means concentric with said first pump means connected to and aligned on a common shaft positioned within a second conduit means concentric with said first conduit means, said first and second pump means being in flow communication with said first and second conduit means,

a second water inlet means to direct water into said second pump means,

a second nozzle means concentric with said first nozzle means connected to said second conduit means to direct water out of said second pump means,

a single source of power in driving connection with both said first and second concentric pump means, and

means to close off one of said inlet means, thereby cutting off said water to one of said pump means after said watercraft has accelerated beyond a low speed high drag region.

2. The invention as set forth in claim 1 wherein said dual pump waterjet is positioned internally within said watercraft, and wherein said first and second nozzle means are concentric one within the other, said concentric nozzle means protruding through a transom of said watercraft to direct water from said dual pumps.