The present invention relates to a to a heat exchanger for a jet pump propelled water craft, such as Rigid Inflatable Boats (RIBS) and jet tenders, but without limitation to same, and to a jet pump incorporating a heat exchanger and to a jet propelled water craft incorporating a heat exchanger.

There is a large market for small powerboats for use as pleasure craft, tenders to larger boats, safety boats, etc. and many small powerboats are of the "rigid inflatable" type known as RIBS. A RIB generally comprises a hull having a rigid bilge portion and an inflatable bulwark defining an outer periphery of the vessel. RIBS are particularly suited for use as tenders, safety boats and for use in confined areas.

Many RIBS are powered by outboard engines which are normally mounted on brackets at the stern of the boat. However, these can be unsightly and noisy and higher specification RIBS therefore generally comprise an inboard engine which is concealed beneath a quarter deck or seat of the boat. Such engines are most usually water cooled, and whilst open circuit cooling systems are known, most use a closed loop cooling system in which an engine driven pump circulates a cooling liquid, such as a water/glycol mixture through the cooling circuit which includes a heat exchanger. The heat exchanger typically takes the form of a plate mounted on the hull of the boat so as to be in contact with the water in which the boat is being operated and having connected thereto heat conducting pipes through which the cooling liquid flows. By this means, as the boat moves through the water, heat transferred to the plate from the engine cooling water is subjected to the cooling action of the external water with which it is in contact.

Some RIBS are of the "jet propulsion" type which utilise an inboard engine driving a "jet pump", rather than a conventional engine screw propeller. In a "jet pump" design the engine is connected to an impeller of a jet pump assembly by a prop shaft. The jet pump assembly is disposed in a "jet tube" which has a water inlet aperture though which water, for example sea water, can enter the jet pump and be pumped by the impeller and forced out of an outlet. The boat can be propelled forwards or backwards in the water according to the direction of thrust of the water jet and steered by vectoring the thrust from the jet pump using a movable nozzle or other vector adjusting means.

The present invention is particularly concerned with a heat exchanger for a watercraft that uses a jet pump propulsion system and which is driven by a water cooled engine. Usually a plate type heat exchanger of the above described type is used. These have the disadvantage of requiring a large surface area to achieve the desired cooling efficiency and hence add to the weight of the boat. Furthermore, because these types of craft frequently use a planning hull, the heat exchanger has to be positioned towards the rear of the hull to ensure adequate water contact in use. This dictates positioning the jet amidships which can give impaired handling and weight distribution. It may also dictate using longer pipe runs in the cooling circuit with a consequential weight penalty and an increased likelihood of the pipes becoming blocked. Additionally, the cooling efficiency of the plate type heat exchanger is reduced quite considerably when the vessel is stationary.

The present invention seeks to address some of the problems associated with the use of a hull mounted plate heat exchanger by dispensing with it. One prior art proposal for doing this is described in GB2363453 in which a marine jet drive incorporates a heat exchanger. The heat exchanger comprises a stator in the jet tube which has several hollow vanes connecting an inlet manifold of the heat exchanger with an outlet manifold of the heat exchanger. Because the stator vanes lie in the jet tube there is a limit to the number of vanes that can be used if the vanes are not to have the disadvantage of reducing the jet tube cross-section. Thus to achieve the desired effective surface area of the vanes the jet tube size has to be increased or the vanes have to be extended along a greater length of the jet tube.

It is an aim of the invention to provide a heat exchanger for a jet pump propelled watercraft which provides a solution.

Accordingly one aspect of the invention provides a jet pump assembly for a water craft, the jet pump assembly comprising a housing having a through bore accommodating a pump impeller and a heat exchanger, the heat exchanger comprising a chamber disposed outwardly of the through bore and having an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

A second aspect of the invention provides heat exchanger for use in association with a jet tube of jet propulsion water craft, the heat exchanger comprising a chamber which, in use, is disposed around the jet tube or forms a peripheral part of the jet tube, and has an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

A third aspect of the invention provides a water jet propelled water craft having an engine driven pump impeller disposed in a jet tube and a heat exchanger comprising a chamber which, in use, is disposed around the jet tube or forms a peripheral part of the jet tube and has an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

The water craft may be a RIB. The pump impeller is preferably driven from an engine, usually an internal combustion engine, and usually a water cooled engine. An engine driven pump circulates the engine coolant, e.g. water or a water glycol mixture, through the aforedescribed heat exchanger which form part of a closed circuit system in order to cool the engine.

A plate type heat exchanger may have a size of say 200mm x 200mm giving a surface area of 0.02m ² . Where the heat exchange chamber is formed around a jet tube of say 150mm diameter, the same surface area can be achieved over a length of 85mm.

The ability to make the heat exchanger so compact allows the heat exchanger to be formed as part of the housing of the pump impeller. Alternatively, it may comprise one or more housing units that are positioned around the jet tube or which themselves form a part of the jet tube. The heat exchanger may comprise an annular housing having an inner bore that forms the or a part of the bore of the jet tube. A series of housings may be used in combination to provide the required surface area in contact with the water in the jet tube. An advantage of placing the heat exchanger in the jet flow is that even when the pump impeller is at idle and the water craft stationary there will be some flow in the jet tube and therefore over the heat exchanger surface.

Optional, preferred and/or advantageous features of the heat exchanger are set out below. In one embodiment the heat exchange chamber forms a water jacket disposed radially outwardly of the jet tube bore. The water jacket at least partially surrounds the jet tube, but more preferably completely surrounds it. An annular heat exchange chamber is preferred. A particularly convenient and compact arrangement arises where the water jacket is part of the jet pump assembly and the water jacket has a plurality of baffles which serve to increase the length of the flow path for the cooling fluid between the inlet and outlet thereof. More particularly those baffles are disposed generally radially and spaced apart circumferentially. Preferably, adjacent baffles extend in from opposite axial ends of the housing and terminate short of the other end thereof to define a respective opening in the flow channel. The staggered baffles comprise an alternating series of first and second baffles. This staggered arrangement of the baffles serves to turn the flow direction through substantially 180 degrees at each opening thereby considerably increasing the length of the flow path and hence the cooling efficiency of the heat exchanger. The number of baffles and the axial and radial extent of the water jacket is determined by the cooling requirements. In one embodiment the baffles are aligned parallel to the axis of the jet tube and the axis of rotation of the pump impeller where provided. However they could be disposed at other angles where this is found to improve the flow characteristics and/or avoid hot spots. The chamber extends by up to 360° around the jet tube.

The aforementioned heat exchange chamber preferably forms part of a closed loop cooling system and is usually used for cooling the coolant of the engine. However, it will be readily understood that the heat exchanger could be used for cooling other fluid systems. For example it may be used as an oil cooler or an intercooler for induction air. It follows that there may be more than one heat exchanger with each serving a different purpose or that the heat exchanger may incorporate more than one cooling circuit. The other cooling circuits may be part of open or closed circuits. A preferred embodiment of the heat exchanger includes an aperture opening into the bore of the jet tube which serves as a fluid pick up point for a secondary coolant system. The secondary coolant system takes liquid from the jet tube and may supply it to an intercooler or an exhaust outlet or both as part of an open circuit cooling system. Alternatively the may be several such apertures supplying discrete coolant circuits.

The present invention will now be described by way of example only with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic side view of a prior art jet propulsion boat,

Figure 2 is a diagrammatic side view of a jet propulsion boat embodying the invention,

Figure 3 is a perspective view from one end and one side of a jet pump embodying the invention,

Figure 4 is a perspective view from one end and the other side of the jet pump of figure 3 with the outer casing removed, and

Figure 5 is a perspective view from the other end and above of a jet pump of figure 3 with the outer casing removed.

The invention is described by way of example in relation to its application to cooling in a water craft provided with a jet propulsion tube. Referring firstly to figure 1, a prior art jet propulsion Rigid Inflatable Boat (RIB) is illustrated which comprises a rigid hull portion 12 and an inflatable tube 14 extending around the rigid hull portion 12 to form gunwales. The RIB has a central passenger area (not illustrated) with main deck (not illustrated) upon which users can stand or upon which cargo can be placed. The hull is provided with a jet tube 18 which has a sea water inlet 20 and an outlet 22. A water cooled internal combustion engine 16 is mounted in the hull and has a prop shaft 26 which drives a pump impeller 24. The pump impeller 24 is mounted for rotation in the jet tube 18. A steering nozzle 26' is provided at the outlet end of the jet tube 18. A heat exchanger plate 30 is mounted on the hull to towards the stern of the craft and aft of the jet outlet 22. Pipes 28, 29 extend from the water jacket of the engine to the heat exchanger plate to circulate the cooling water under the action of an engine driven water pump (not illustrated). It will be seen that this dictates positioning the jet tube amidships which can have an adverse effect on handling and weight distribution.

Reference is now made to figure 2 which illustrates diagrammatically an embodiment of jet propulsion boat having the same basic features as that described with reference to figure 1 save for the fact that the heat exchanger plate 30 at the stern of the craft is dispensed with and replaced by a heat exchanger 30' that is disposed in a position at least partially surrounding the jet tube 18 of the craft. However it will be understood that the water craft does not have to be a RIB. More particularly, the heat exchanger comprises a chamber or water jacket 19 surrounding the jet tube and more preferably still is disposed in close proximity to the jet pump impeller 24 although that is not to say that it cannot be disposed at any convenient position along the jet tube, for example fore and/or aft thereof when not forming part of the pump impeller assembly itself. Indeed several heat exchange modules may be provided at different positions as designated by way of example by references a, b and c. Engine coolant pipes 28, 29 connect with appropriately positioned ports on the heat exchanger as described further hereinafter. The position in which they are shown in this figure is merely diagrammatic. Preferably the heat exchanger comprises a housing that is inserted into the jet tube and preferably that housing incorporates the jet tube impeller as described further hereinafter with reference to figures 3, 4 and 5. Referring firstly to figure 3, there is illustrated a jet pump assembly comprising a body 50 having a through bore 52 defined by inner wall element 53. The diameter of bore 52 corresponds substantially to the diameter of the jet tube e.g.18 of the vessel in which the jet pump is to be used. A pump impeller (not illustrated) is mounted for rotation in the bore 52 and supported relative thereto by radial members 54 (see figures 4 and 5). A bearing housing for the impeller is shown at 56. An outer cylindrical casing 58 which is larger in diameter than the inner wall element 53 is fitted to the body 50 and forms the outer wall of a fluid coolant chamber hereinafter referred to as a 'water' jacket for ease of reference as the coolant fluid for the particular example described is likely to be a water/glycol mixture. However it will be understood that the coolant may be another type of fluid as mentioned elsewhere in this description.

The construction of the 'water' jacket is best understood and further described with reference to figures 4 and 5 in which the outer casing 58 has been removed. The body has axially spaced annular flanges 60, 62 which in practice carry circumferential sealing elements 64, say in the form of O ring seals, disposed in seal grooves, to make a fluid tight seal with the outer casing. A flow channel is defined between the inner wall element 53, the end flanges 60, 62 and the outer casing 58 by the further provision of a plurality of baffles 70, 72. Baffles 70 extend in an axial direction from flange 60 toward flange 62 but terminate before reaching it to define a openings 74. On the other hand baffles 72 extend from flange 72 towards flange 70 but terminate before reaching it to define openings 75. This configuration defines a flow path with numerous reverses in direction (see arrows F) and thereby increases the length of the flow path significantly compared with basic circumference of the jacket. End flange 60 incorporates an inlet connection (see arrow I) via which the hot fluid coolant enters the jacket of the heat exchanger and an outlet connection (see arrow O) via which the cooled engine coolant fluid returns to the engine.

In the preferred application to a jet pump propelled water craft such as a RIB, the aforedescribed flow channel is part of the closed circuit engine coolant system. The embodiment of figures 3, 4 and 5 also has a pick-up point for a secondary coolant circuit which feeds coolant (e.g. lake or sea water) from the jet tube to an intercooler and exhaust outlet. The pick-up point is formed by a bore 90 in a boss 92. The bore 90 opens into bore 52 which in use forms part of the jet tube of the craft and merges with a cross bore with an outlet connection in flange 60 (see arrow R showing the exit flow direction). Also illustrated is a wall 94 extending between the end flanges of the housing and separating the hot inlet side of heat exchange chamber from the cold outlet side. Lugs for fixing the assembly in position in the jet tube are shown at 96.

It will be readily understood that by omitting the aforedescribed radial members 54 and bearing housing 56 the heat exchanger can be formed as a self-contained unit, for incorporation in the jet tube rather than combined with the pump impeller assembly. It will also be understood that the heat exchanger can be used in jet pump propelled water craft other than RIBS.

The following statements are not the claims, but relate to various aspects of the invention:

Statement 1. A jet pump assembly for a water craft, the jet pump assembly comprising a housing having a through bore accommodating a pump impeller and a heat exchanger, the heat exchanger comprising a chamber disposed outwardly of the through bore and having an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

Statement 2. The jet pump assembly of statement 1 in which the chamber has opposite end walls and the staggered baffles comprise an alternating series of first and second baffles comprising a first series of baffles that extend from one end wall towards the opposite end wall and a second series of baffles that extend from the opposite end wall toward said one end wall.

Statement 3. The jet pump assembly of statement 1 or 2 in which the baffles define an oscillatory and circumferential flow channel between and the inlet and outlet. Statement 4. The jet pump assembly of statement 2, 3 or 4 in which the chamber extends by up to 360° around the through bore.

Statement 5. The jet pump assembly of any preceding statement in which the heat exchanger includes an aperture opening into the through bore which serves as a fluid pick up point for a secondary coolant system.

Statement 6. The jet pump assembly of any preceding statement in which the baffles are parallel to one another and extend parallel to the through bore axis.

Statement ?. The jet pump assembly constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings of figures 3, 4 and 5.

Statement s. A heat exchanger for use in association with a jet tube of jet propulsion water craft, the heat exchanger comprising a chamber which, in use, is disposed around the jet tube or forms a peripheral part of the jet tube, and has an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

Statement 9. The heat exchanger of statement 8 in which the chamber has opposite end walls and the staggered baffles comprise an alternating series of first and second baffles comprising a first series of baffles that extend from one end wall towards the opposite end wall and a second series of baffles that extend from the opposite end wall toward said one end wall.

Statement 10. The heat exchanger of statement 8 or 9 in which the baffles define an oscillatory and circumferential flow channel between and the inlet and outlet.

Statement 11. The heat exchanger of statement 8, 9 or 10 in which the chamber extends by up to 360° around the through bore.

Statement 12. The heat exchanger of any of statements 8 to 11 in which the heat exchanger includes an aperture opening into the through bore which serves as a fluid pick up point for a secondary coolant system.

Statement 13. The heat exchanger of any of statements 8 to 12 in which the baffles are parallel to one another and extend parallel to the through bore axis.

Statement 14. A heat exchanger constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings of figures 3, 4 and 5 when modified to exclude the pump impeller.

Statement 15. A water jet propelled water craft having an engine driven pump impeller disposed in a jet tube and a heat exchanger comprising a chamber which, in use, is disposed around the jet tube or forms a peripheral part of the jet tube and has an inlet and an outlet for fluid to pass through the heat exchange chamber in use, and a series of staggered radial baffles in the chamber defining an oscillatory and circumferential flow path for the fluid between the inlet and outlet.

Statement 16. The water jet propelled water craft of statement 15 in which the chamber has opposite end walls and the staggered baffles comprise an alternating series of first and second baffles comprising a first series of baffles that extend from one end wall towards the opposite end wall and a second series of baffles that extend from the opposite end wall toward said one end wall.

Statement 17. The water jet propelled water craft of statement 15 or 16 in which the baffles define an oscillatory and circumferential flow channel between and the inlet and outlet.

Statement 18. The water jet propelled water craft of statement 15, 16 or 17 in which the chamber extends by up to 360° around the through bore.

Statement 19. The water jet propelled water craft of statement 15, 16 or 17 in which the chamber extends by up to 360° around the through bore.

Statement 20. The water jet propelled water craft of any of statements 15 to 19 in which the heat exchanger includes an aperture opening into the through bore which serves as a fluid pick up point for a secondary coolant system.

Statement 21. The water jet propelled water craft of any of statements 15 to 20 in which the baffles are parallel to one another and extend parallel to the through bore axis.

Statement 22. The water jet propelled water craft constructed and arranged substantially as hereinbefore described with reference to the accompanying drawing of figure 2 or as modified according to figures 3, 4 and 5.