Water-crafts or vessels mean here all kinds of marine vessels, like for exam- ple cruisers, passenger ships, ice breakers and different cargo ships. Ar- rangements are already known, in which a water-craft is provided with two mechanically connected propellers with rudders behind them, two or three separate pod-propulsion devices or a propeller, behind which there is a con- tra-rotating propeller in a pod-propulsion device. The last mentioned has been disclosed in a WO-publication 01/54971, in which the pod-propulsion unit has been indicated by the reference numeral 4 and the propeller by nu- meral 3.

The prior art solutions include substantial disadvantages. Firstly, the me- chanical propeller arrangement has long shaft lines and shaft supports out- side the hull of water-craft, which lead to a non-uniform wake field.

Steerable rudder-propeller devices or pod-propulsion devices have become more general in water-crafts. Since these devices are turnable, their thrust force can be utilized for steering of the water-craft.

A disadvantage with an electric arrangement of two or more pod-propulsion devices are the high costs, because efficient pod-propulsion devices require engine-driven generators together with their power control systems. These are expensive, heavy and large. For instance in RoRo vessels handling of cargo becomes more difficult because of the engine rooms and gaps required

by the machinery, since these are partly located above the cargo deck. This means that several disadvantageous narrow parts are formed in the cargo space, whereby the rear end of the cargo space remains narrow. The heavy electric machinery leads further to a disadvantageous location of the dis- placement's centre of gravity in the longitudinal direction.

In the contra-rotating pod/propeller-combination there is only one steering device, which is often considered as a disadvantage from the viewpoint of reliability.

An object of the present invention is to eliminate the drawbacks of the prior art and to provide a novel solution advantageous as to its costs and enabling, where applicable, better utilization of the cargo space of the water-craft The aims of the invention can be achieved as is disclosed in claim 1 and in the other claims. According to the invention the steering propulsion devices are arranged in the aft of the water craft on both sides of the said at least one main propulsion device so that the steering of the water-craft is continu- ously provided by means of the steering propulsion devices without any separate rudder means of the like to be functionally connected to said at least one main propulsion device.

The invention is based on the use of turnable steering propulsion devices in a water-craft so that they alone provide steering and additionally they partici- pate in moving the water-craft forward. A major part of the forward or backward propulsion is generated by a separate thrust device e. g. a large propulsion unit or large propulsion units. An important advantage of the solu- tion according to the invention is the fact that the upper end of the pod- propulsion devices fits below the cargo deck. Since the fully electric machin- ery of conventional large pod-propulsion devices is heavier and larger than the machinery to be utilized according to the invention, the invention allows for increased cargo capacity and handling of cargo becomes more efficient

and easier. Furthermore, the solution is more economic and easier to put technically into practice than the known solutions. The cargo deck can be lowered, the dimensions of the water-craft can be more economic and, com- pared with one centre propulsion device, two propulsion devices provide bet- ter reliability, which is important especially for the manoeuvrability of a pas- senger ship. Further, when separate main propulsion devices and steering propulsion devices are provided no supplementary output is used unnecessar- ily in manoeuvring.

According to the invention there is an even number of the steering propulsion devices and the propeller part of the steering propulsion devices is stationar- ily located outside of the hull of the water-craft. There is one or more main propulsion devices and for instance a propeller or a water-jet device may function as the main propulsion device.

The water-craft's at least one main propulsion device is located essentially in the aft centre part of the water-craft and the steering propulsion devices are positioned to the sides of the propulsion device being thus located in the lat- eral parts of the water-craft near the sideboards thereof. A high efficiency is obtained when the main propulsion device is placed as far as possible in the water-craft's aft and no protruding parts increasing the resistance are needed in the rear side of the main propulsion device. Since no shaft bearings are needed, a uniform wake is created. The steering propulsion devices provide an excellent manoeuvrability even in rough weather conditions, also at low speeds for instance less than 5 knots.

According to the invention, the output of the steering propulsion devices need not be high. The output required by the steering propulsion devices is less than 50% of the common shaft output of the main propulsion device and of the steering propulsion device. Shaft output means here the usual output obtained from the devices at maximum i. e. the nominal output taken by the main propulsion device and the steering propulsion device, which can

be measured from the outlet shaft of the device. The propulsion device itself is connected by means of a horizontal or almost horizontal shaft or shafts to a prime mover that may comprise one or more diesel engines and/or electric engines and/or gas turbines.

Further, since the steering propulsion devices are installed on both sides of the one or more main propulsion devices substantially near the outboard of the water-craft, they can be relatively small and can thus be installed under the cargo space of the water-craft. By doing so, a space can be formed un- der the cargo space for the maintenance and inspection of the steering pro- pulsion devices.

Also other alternative solutions are conceivable, in which there can be in the middle one or more water-jet devices as a main propulsion device e. g. if the speed of the water-craft is high. Also in this case, the steering propulsion de- vices are at the side and a major part of the power used for moving forward is provided by the main propulsion device.

In the following the invention is described by way of example only with ref- erence to the accompanying drawings, in which - Figures 1 A and 1B show a water-craft provided with an arrangement ac- cording to the invention as a side view and viewed from below, - Figures 2A and 2B show alternative solutions relating to main propulsion devices and steering propulsion devices, and - Figures 3A and 3B show further alternative solutions relating to main pro- pulsion devices and steering devices.

According to Figures 1A and 1 B, the arrangement is formed by a water-craft or a vessel 1 together with steering propulsion devices 2 and a main propul- sion device 3. In this solution, the steering propulsion devices, even in num- ber, have been placed quite close to the outboard 6 of the vessel. Diesel en- gines, indicated by the reference numeral 4, serve as prime mover for the

main propulsion device, the output of which is transferred to the main pro- pulsion device by means of a shaft 5. As the steering propulsion devices in the solution according to the invention need not be large, they do not require much space and the maintenance space 8 they need, in which maintenance staff 7 may go for checking, and when required, repairing the steering pro- pulsion devices, is situated advantageously below the cargo space 10. In this way the whole cargo space can be put into use and there are no previously needed narrowing parts, but the whole area can be utilized at maximum e. g. by loading onboard trucks and other cargo on wheels 9.

In Figure 2A, the upper view shows a main propulsion device 3 and a steer- ing propulsion device 2. Furthermore, a couple of examples of a steering pro- pulsion device is shown in different positions 2a and 2b. When the steering propulsion device is in position 2b, turning of the vessel into a desired direc- tion is provided. If there is a need for boosting the turning, also the other steering propulsion device 2 is turned, respectively, into position 2b simula- neously with the previous one. In Figure 2B, one main propulsion device 3 has been replaced by two separate main propulsion devices 3a and 3b.

In Figure 3A, in addition to the steering propulsion devices 2, there is pro- vided an alternative solution to the traditional propeller and in this view a wa- ter-jet device 11 is used as a main propulsion device. The Figure 3B view is a supplementary variation of the Figure 3A, in which there are more than one water-jets, in this solution three water-jets 11 a, 11 b and 11 c. Advanta- geously, also two water-jets 1 1 a and 1 1 c can be installed.

Within the scope of invention ; solutions also differing from the above de- scribed are feasible. The solution can be applied to all kinds of water-crafts.

For example, in war ships and cruisers the solution makes possible a diversi- fied driving profile. The main mover of the steering propulsion devices can also be placed above the cargo deck e. g. around the smoke stack, in which case supplying of electricity also to other parts of the vessel is easy. In cruis-

ers, this makes possible flexible distribution of electric power between the hotel load and the propulsion devices.

It is clear to the one skilled in the art that the invention is not restricted to the embodiments described above, but different applications thereof are fea- sible within the inventive idea defined by the ensuing claims.