Technical Field The present invention relates to a heat exchanger for a water-borne vessel such as a ship or boat. In particular, though not necessarily, the invention relates to a heat exchanger suitable for cooling an electric motor of a water-borne vessel.

Background

Water-born vessels such as ferries and other light commercial vessels are typically driven by high powered inboard internal combustion engines. These engines generate a significant amount of heat and the engines therefore require cooling to ensure that the engine temperature remains within acceptable operating limits. Cooling is also required for lower power engines such as those used on yachts and other pleasure crafts.

Inboard engines are typically cooled by circulating coolant around a circuit including a heat exchanger and the engine. The coolant absorbs heat from the motor, and gives off the heat at the heat exchanger. Various types of inboard engine heat exchangers are known and may involve the use of sea water (or fresh lake or river water) to absorb the heat from the coolant.

This may involve pumping cold seawater from beneath the vessel into the heat exchanger and then pumping the heated seawater back into the sea.

German patent application number DE-1 02005002456 discloses a heat exchanging keel for cooling an engine. The keel comprises integrated cooling coils through which coolant flows. Whilst the keel provides an extremely large surface area and therefore excellent heat exchange capacity, it is an expensive component to construct for a new build. It is also difficult to adapt or retrofit a keel in the case of an existing vessel. Of course, many vessels such as motorboats do not have a keel so this solution is not appropriate.

Summary of the Invention

It is an object of the present invention to provide a cooling system for a water-borne vessel that is simple and cheap to produce, is straightforward to fit or retro-fit. and does not negatively impact on vessel handling characteristics to a significant extent.

According to a first aspect of the present invention there is provided a cooling system for a water-borne vessel comprising a propeller shaft extending from a bow end at which the shaft is driven by an inboard electric motor to a stern end at which a propeller is fixed to the propeller shaft, the cooling system. The cooling system comprises a strut in the form of a highly thermally conducting structure for attachment to the bottom of the vessel's hull, at the stern end, for supporting the propeller shaft of the vessel, the strut comprising a fluid inlet, a fluid outlet, and a channel or channels within the strut for transporting fluid between the fluid inlet and fluid outlet, one or more fluid conduits for location inside the vessel's hull for coupling the fluid inlet and fluid outlet to the inboard electric motor and/or batteries thereof to be cooled, and a pump for circulating a fluid through the conduits and said channel(s). Cooling of a fluid of the cooling system is provided substantially only as it flows through the strut. The strut may comprise a bearing for supporting a propeller shaft and for facilitating rotation of the shaft with the strut. The strut may be formed substantially of a metal or metal alloy, for example stainless steel, brass, aluminium, or an allow of brass and aluminium.

According to a third aspect of the present invention, there is provided a vessel comprising the cooling system of the above first aspect of the invention.

Brief Description of the Drawings

Figure 1 is a side view of a stern portion of a water-borne vessel;

Figure 2 is a perspective view of a heat exchanger according to an embodiment of the invention;

Figure 3 is a cut-away view of the heat exchanger of Figure 2; and

Figure 4 illustrates a cooling system according to an embodiment of the invention. Detailed Description

The marine industry is increasingly interested in the use of electric motors to propel vessels. This is due to a number of factors including environmental, performance, and efficiency. One advantage of electric motors is the reduced amount of heat that they produce, meaning that cooling systems can be simplified. In particular only a relatively small heat exchanger may be required. One might consider providing a dedicated component beneath a boat ^' s hull and which has a surface area exposed to the sea water. However, whilst such a component may provide efficient cooling, it adds an extra cost and may also add to the hull's drag factor. Figure 1 is a side view of a water-borne vessel 1 . The vessel 1 comprises a hull 2, propeller 3. propeller shaft 4. propeller shaft strut 5. and rudder 6. When the vessel is in water, the propeller 3. propeller shaft 4. propeller shaft strut 5 and rudder 6 are below the water line. The propeller shaft 4 is driven to rotate by a motor inside the vessel, and in particular by an inboard electric motor (not shown in the Figure). Rotation of the propeller shaft 4 results in rotation of the propeller 3, and hence propulsion of the vessel 1 through the water. The propeller shaft strut 5 supports the propeller shaft 4 within a bearing such that the shaft is allowed to rotate within the strut 5 but is prevented from flexing and vibrating (to any significant extent) and the propeller 3 prevented from coming into contact with the hull 2. Figure 2 is a perspective view a propeller shaft strut 5 according to an embodiment of the invention whilst Figure 3 is a cut-away view of the same propeller shaft strut 5. In this embodiment the propeller shaft strut 5 is configured to operate also as a heat exchanger 7. The strut 5 comprises a cooling fluid inlet 8. a cooling fluid outlet 9. a cooling channel 10 and a propeller shaft channel 1 1 into which a bearing is integrated (not shown). The cooling channel 10 allows fluid entering through the cooling fluid inlet 8 to circulate within the propeller shaft strut 5 and out through the cooling fluid outlet 9. The fluid may be water or another suitable liquid. The channel 1 0 is isolated from the outer surface of the strut 5, to prevent mixing of cooling fluid inside the strut and water outside the strut. The propeller shaft strut 5 is a highly thermally conducting structure which in use is located below the waterline. For example, the propeller shaft strut 5 may be cast or machined out of bronze or stainless steel. The propeller shaft strut 5 is preferably located in front of the propeller 3 in the direction of motion of the water vessel 1 . The temperature of the propeller shaft strut 5 is thus very close to the temperature of the water surrounding the propeller shaft strut 5.

Whilst Figure 3 illustrates a simple generally U-shaped cooling channel 10, the channel may have a more convoluted shape, such as a zig-zag shape, so as to increase the cooling surface area of the channel that is exposed to coolant. The cooling channel 1 0 is preferably near the outer surface of the propeller shaft strut 5 so as to enable efficient heat exchange between the cooling fluid and the surrounding water.

Whilst the propeller shaft strut 5 is a relatively small component, and therefore is able to provide only limited cooling capacity, it has been found that this is sufficient for certain efficient electric motors. Moreover, the modified propeller shaft strut 5 can be easily retro-fitted to existing vessels, for by example replacing an existing propeller shaft strut with a modified propeller shaft strut. Furthermore, because the propeller shaft strut 5 is a direct replacement of an existing propeller shaft strut on a vessel, the handling characteristics of the vessel, such as manoeuvrability and top speed, are not adversely affected to any significant extent.

Figure 4 illustrates schematically a cooling system 12 incorporating the propeller shaft strut 5 described above. The cooling system comprises the modified propeller shaft strut 5. coolant pump 1 3 and coolant tubes or pipes 14. The cooling system 12 cools an electric motor 1 5 that heats up in use and requires cooling. The cooling system 12 is shown coupled directly to the electric motor 1 5 but indirect coupling is also possible. For example, the electric motor may have an internal cooling system with its own heat exchanger in which case the cooling system 12 provides a means for cooling the internal heat exchanger.

In use. the coolant pump 13 circulates cooling fluid around the cooling system 12. Lower temperature cooling fluid flows from the heat exchanger 7, through the coolant pump 13 and to the device 1 5. The cooling fluid absorbs heat emitted by the device 15 and the higher temperature cooling fluid flows to the heat exchanger 7. The heat exchanger 7 conducts heat away from the cooling fluid, thus reducing the temperature of the cooling fluid before the cooling fluid is fed back towards the device.

In the embodiment shown in Figure 4, the cooling system is used to cool an electric motor. However the invention may be used to cool any device that requires moderate cooling in operation. For example, batteries and air conditioning components may be cooled by the cooling system.

It will be appreciated by persons skilled in the art that various modifications may be made to the above embodiments without departing from the scope of the present invention.