FIELD OF THE INVENTION

This invention relates to propulsion of marine vessels. BACKGROUND TO THE INVENTION

Attempts at improving energy efficiency of most human activities have increased drastically in recent years, following widespread concerns about global warming, but marine propulsion systems have evolved very little and a need still exists to improve on the energy efficiency of marine propulsion systems.

Propulsion systems in most forms of transport should preferably be as compact as possible, but this is particularly so in many marine vessels, where the space that would most conveniently be occupied by the propulsion system, could also be used most conveniently for passengers or payload. As a result, marine propulsion systems should be as compact as possible, e.g. it should not protrude into a vessel's cockpit, obstruct passengers' view, etc.

The present invention seeks to provide compact, powerful and energy efficient propulsion for marine vessels.

SUMMARY OF THE INVENTION

According to the present invention there is provided a propulsion system for a marine vessel, said propulsion system comprising:

a source of electrical power;

an electrical accumulator, connected to receive electrical power from the electrical power source;

an electric motor, connected to receive electrical power from the electrical

accumulator;

a drive shaft, connected to receive rotational power from the electric motor; and a propeller shaft, connected to receive rotational power from the drive shaft;

wherein said electric motor, drive shaft and propeller shaft are housed in a power train that is configured to pivot about a generally horizontal axis, relative to a transom of said vessel.

The electrical power source may include a source of rotational power and a generator, said generator being connected to receive rotational power from the rotational power source and to supply power to charge the accumulator. The source of rotational power may be a gas turbine and the gas turbine and electrical generator may have a common shaft.

The drive shaft may be connected coaxially to the shaft of the electric motor.

The powertrain may include an upper unit which houses the electric motor and a lower unit which houses the propeller shaft, the lower unit being pivotable relative to the upper unit, in steering directions. The lower unit may be pivotable relative to the upper unit about the axis of the drive shaft.

The propeller shaft may extend at an obtuse angle relative to the drive shaft. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 is a schematic side view of a marine propulsion system in accordance with the present invention, in use while cruising; and

Figure 2 is a schematic side view of the marine propulsion system of Figure 1 , with its powertrain tilted up.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings a marine propulsion system in accordance with the present invention is generally indicated by reference numeral 10. The system 10 includes a microturbine 12, which includes components forming an electric generator and a gas turbine, on the same shaft. Preferably, the gas turbine of the microturbine 12 can operate using a wide variety of fuels and can operate with very low emission levels. Suitable microturbines are commercially available, e.g. microturbines from Capstone Turbine Corporation in California, USA.

The microturbine 12 is electrically connected and provides electrical power to an accumulator in the form of a lithium ion battery 14, which provides electrical power to a DC electric motor 16, as well as ancillary sub-systems, such as a hydraulic power pack 18 and a water pump 20. The supply of electrical power to the motor 16 and ancillary sub-systems is controlled in a controller 22, which receives input from controls at the helm, e.g. a selection of forward, neutral, or reverse on a "gear selector" 24, and which feeds information signals for display on a helm station 26.

The motor 16 is directly connected to a driveshaft 28 and these components form an upper unit 30 of the powertrain of the system 10. The upper unit 30 is pivotally supported to extend through an aperture in the transom 32 of the vessel, inside a cavity 34, formed inside a powertrain housing 36 that is fixedly mounted to the transom. The upper unit 30 protrudes through the transom 32, with fixed transom covers enclosing the cavity 34 laterally, astern of the transom and with a styling cover 40 pivoting along with the upper unit 30 and extending generally between the transom covers 38.

A lower unit 42 of the power train is attached to the lower, stern end of the upper unit 30 and houses a lower portion of the driveshaft 28, which is connected through an obtuse angle to a propeller shaft 46, via a reduction gearbox 44. A propeller (not shown) is carried by the propeller shaft 46.

The lower unit 42 can rotate relative to the upper unit 30 about the axis of the drive shaft 28 and this rotation is controlled by a hydraulically or electrically powered steering assembly 48. This rotation of the lower unit 42 changes the orientation of the fairing 50 of the lower unit, as well as the propeller shaft 46 and the vessel is steered by this rotation, which rotates the lower unit 42 in steering directions about the axis of the driveshaft 28.

The upper unit 30 and lower unit 42 together form the powertrain of the system 10 and are shown in Figure 1 in a typical position when the vessel is being propelled forward in a cruise condition, but the powertrain 30,42 can pivot up and down from this position, about a generally horizontal trim/tilt axis, relative to the vessel, inside the cavity 34. Typically, the powertrain 30,42 can pivot about 5 degrees down and 29 degrees up, to a position shown in Figure 2. The pivotal movement of the powertrain 30,42 is driven by hydraulic rams 52 or linear motors, extending between the transom 32 and a lower part of the upper unit 30 of the powertrain.

The pivotal moment arm (i.e. the distance between the pivotal axis and the propeller shaft 46) of the pivotal movement of the main powertrain 30 and lower unit 42 is longer than those of conventional stern drives - thus providing better control over the trim of the propulsion system 10. Likewise, the moment arm between the propeller shaft 46 and the hull of the vessel is longer than in conventional stern drives - thus providing more effective trim.

Exhaust gasses from the microturbine 12 flow along a jacketed exhaust riser 54, which extends downwards and which is connected to the upper unit 30 via bellows 56 and extends along a passage defined inside the upper unit 30, a passage defined inside the lower unit 42 and to an annular passage around the propeller shaft 46.

The system 10 can be installed in a vessel with a conventional transom 32, in which a suitable aperture is cut, to form the cavity 34, when the powertrain housing 36 is attached to the inside of the transom and the transom covers 38 are attached to the stern of the transom. The vessels thus need not be manufactured with a different transom 32, specific to the system 10.

In use, the system 10 can be operated in different modes. If the battery 14 is charged sufficiently, the microturbine 12 can be off completely and the motor 16 can be driven only from the battery. This would, for instance be advantageous when quiet operation is required. If maximum power is required, the microturbine 12 can run and provide power, while the motor 16 is powered from the battery, using what power the microturbine supplies, as well as additional power from the battery. When cruising, i.e. when moderate power is required, the motor 16 can be powered from the battery 14 and the microturbine 12 can run intermittently to charge the battery, when needed.

The microturbine 12 is only configured to operate at an optimal speed and

accordingly, it can operate very efficiently, but it does not provide different power levels. Compensation for varying power demand from the motor 16 is made by accumulating energy in the battery 14. The system 10 thus holds the advantages that it is very energy efficient (due to only optimal operation of the microturbine 12), can occasionally provide more power than the microturbine 12 can provide (by boosting power from the battery 14) and can operate quietly (when running only on battery power).

The system 10 holds another advantage of being able to operate on various fuel types, which could be very useful in cases of fuel shortages and/or in defence applications.

The system 10 holds a further advantage in that the motor 16 can operate as an electromechanical brake, to arrest propeller rotation.

As can be seen in the drawings, the system 10 is very compact, fitting snugly against the transom 32 and not protruding significantly into the inside of the vessel and also not protruding above the transom.

In other embodiments, instead of a microturbine, any other source of rotational power, e.g. a diesel engine, can be used to drive a generator and supply power to the battery 14. Instead or in addition, a wide variety of other sources of electrical power may be used to supply power to the batter 14, e.g. the battery may be charged from land-based power supplies (shore power), when the vessel is docked, or may be charged from solar or photovoltaic sources.