The invention relates to a propulsion and steering unit for a vessel comprising an integrated propeller/torpedo/rudder arrangement, wherein the torpedo is a part of a rudder horn fixedly mounted in a ship, and where the maximum diameter ofthe torpedo is greater than the diameter ofthe propeller hub.

Fuel savings, reduction of emissions and improved manoeuvrability are important conditions in the development of ships and ship equipment. The main objective of the present invention, which relates to an integrated system consisting of rudder, torpedo and propeller, is to improve propulsion efficiency and manoeuvring characteristics in relation to ships having conventional systems with separate rudder and propeller.

British Patent Application No. 762445 makes known different types of the traditional Costa bulb, which have greater maximum diameter than the propeller hub, and which are arranged on the rudder behind the propeller. In the case of the structures taught here, the water flow between the hub and the front edge of the bulb will take place in such manner that the resistance of the bulb will increase. The solutions described are designed according to the principle that contraction of the propeller slip stream is wholly or partly eliminated by locating the front edge of the bulb close to the after end of the propeller blades.

British Patent Publication No. 385607 makes knowτi bodies mounted behind the propeller hub in such manner that in the case of fixed propellers they represent an extension ofthe propeller hub. Forward of these propeller hub extensions are openings to receive the nut at the rear ofthe fixed propeller.

The diameter of these propeller hub extensions is not greater than that ofthe hub and therefore they will not reduce the contraction ofthe propeller slip stream. The main objective of this known solution is to avoid energy loss caused by cavitation behind the hub.

The transition between hub and extension is designed in such a way. though, that the desired effect is not achieved. However, a more streamlined transition between hub and extension is achieved by increasing the diameter of the propeller hub. An increased hub diameter causes, however, a reduction in the efficiency of the propeller.

Norwegian Patent Publication No. 154,262 also makes known the use of bulbs behind the propeller, which bulbs have a maximum diameter that is greater than the propeller hub. The bulbs are mounted on the moveable rudder blade and have a front edge extending to or ahead ofthe after end ofthe propeller hub, and are also combined with reaction fins. In the case ofthe bulbs taught in the Norwegian patent publication, the water flow between the hub and the front edge ofthe bulb will take place in such manner that the resistance ofthe bulb increases.

According to the invention, an integrated propeller/toφedo/rudder arrangement is proposed, wherein the toφedo is a part of a rudder horn fixedly mounted in the ship, and where the largest diameter ofthe toφedo is greater than the diameter ofthe propeller hub, what characterises the invention being that the propeller hub, together with the toφedo, forms a uniform streamlined profile, the propeller hub being designed to have an increasing diameter in the region from the front edge and aftward.

Thus, according to the invention a streamlined body, termed a toφedo, is used, which has a greater maximum diameter than the propeller hub. The propeller hub and toφedo are designed so that together they form an optimised streamlined profile, i.e., a continuous profile from the front edge ofthe propeller hub to the after end ofthe toφedo, broken only by a narrow gap. The toφedo is mounted fixedly relative to the ship in that it is rigidly secured to the rudder horn. Thus, there is only a minimal rotation gap between the propeller hub (rotating) and the toφedo (stationary)- In the case of a variable pitch propeller, the roots ofthe blades are incoφorated into the streamlined profile.

Additional features ofthe invention will become apparent from the dependent patent claims.

In a preferred embodiment, one or both surfaces in the rotation gap are coated with a tear-proof bearing material. The after part ofthe toφedo ends behind the axis of the rudder stock, and cuts into the rudder blade, which has a notch corresponding to the outline ofthe toφedo. A small clearing is included in this notch so that the rudder blade can swing unimpeded whilst the pressure leakage through the gap is minimal on small rudder deflections. The whole system consisting of propeller blades, propeller hub, toφedo, rudder horn, rudder blade, optional flaps and optional fins is integrated and optimised with a view to optimal propulsion efficiency and manoeuvring characteristics.

In the case of all the known bulbs having a maximum diameter behind the propeller which is greater than the propeller hub, the forward part ofthe bulb profiles is located behind the propeller centre. The forward part ofthe bulbs is designed so that the form resistance ofthe bulb increases and/or is located on a moveable rudder so that the bulb's resistance, and thus the necessary engine output, increase on the small rudder deflections which are necessary to keep the vessel on the planned course.

The propulsion and steering unit according to the present invention is designed so that the toφedo and propeller hub form an uninterrupted streamlined profile. This is done to eliminate more efficiently contraction ofthe propeller slip stream, and also to recover more ofthe energy loss which is caused by vortex shedding and cavitation behind the propeller hub.

In the transition between the actual propeller blade and the root ofthe blade, i.e., behind the quarter-hollows ofthe propeller blade, vortices are formed behind each propeller blade. Owing to the streamlined transition between the rotating propeller hub and the fixed toφedo according to the invention, these vortices will rotate around the toφedo and the energy loss will therefore be recovered in the transition between the toφedo and the front edge ofthe rudder.

None of the structures known hitherto are designed to allow the recovery of this energy loss, and nor are any attempts to exploit this energy loss known to have been described.

Owing to the fact that the propeller hub, together with the toφedo according to the present invention, constitutes a uniform streamlined profile, it is also possible to increase propulsion efficiency by increasing the load along the propeller blades. In the case ofthe bulb structures known hitherto, the transition between the propeller hub, toφedo and rudder has been designed such that it is not possible to achieve any appreciable recovery of this increased energy loss caused by more powerful quarter- hollow vortices and shedding behind the propeller hub.

However, with this integrated system there arise new possibilities of optimising the propeller blade geometry, toφedo and rudder as a unit with a view to increasing propulsion efficiency.

Radial fins mounted on the surface ofthe toφedo can, in certain cases, be used to recover more ofthe rotation energy in the propeller slip stream.

Tests with models have shown that in relation to the known conventional arrangements with rudder bulbs, the new integrated system according to the invention provides a considerably higher degree of propulsion efficiency and thus reduced necessary engine output. The desired effects of using a continuous streamlined profile and toφedo/rudder combination are thus achieved. Tests carried out with models show that in contrast to the previously known bulbs this integrated system gives increased gain on increasing ship speed.

In the case of some types of vessel, the length/breadth ratio of the hull has been steadily reduced. This has resulted in a number of vessels having poor straight line and course stability. The invention, with the fixedly mounted toφedo in the propeller slip stream together with the rudder horn, will impart to the vessels improved straight line and course stability. In particular in the case of vessels which operate on long runs, the invention will reduce necessary rudder use to maintain course and thus reduce fuel consumption further.

The integrated system according to the invention will moreover eliminate hub vortices/shedding behind the hub, and will thus contribute towards a considerable reduction in propeller-induced subsea noise.

The invention will now be explained in more detail with reference to the drawings, wherein:

Fig. l is a lateral view of an example of the invention;

Fig. 2 shows an example ofthe invention where an unbalanced rudder is used;

Fig. 3 is a section through the toφedo arrangement in Fig. 1 ;

Fig. 4 shows two rings which form a part ofthe toφedo; and

Fig. 5 is a perspective view of an embodiment ofthe invention.

In Fig. 1 the main components can be seen: a variable pitch propeller 1 , a toφedo 2, rudder horn with rudder case 3, and a semi-balanced rudder 4. The propeller and rudder are positioned as on traditional ships. The propeller 1 is shown as a variable pitch propeller, but may also have fixed pitch. The illustrated outer contour 5 ofthe propeller hub 6 may either be cast in a single piece with the hub or be a screwed-on or shrunk-on adapter ring having a correct outer contour, adapted to an existing hub.

The toφedo 2, which has its greatest diameter approximately forward ofthe rudder horn 3, is located in the extension ofthe propeller hub 6 and is flanged (screwed) 7 into place on the rudder horn 3. The horn bearing 8 is built into the after end ofthe toφedo 2. The rudder 4 has a notch 9 which accommodates the after end ofthe toφedo 2.

Fig. 2 shows an example of the invention where an unbalanced rudder 10 is used. The rudder horn 1 1 here is extended down to the lower edge ofthe rudder blade 10, and the hom bearing 12 is located at the very bottom. The rudder hom 11 is split by a horizontal flange 13 above the toφedo 14 (for dismounting purposes) and the lower part of the rudder hom is integrated with the toφedo. The rudder blade can be equipped with flaps, if so desired.

Fig. 3 shows a section through the toφedo arrangement in Fig. 1. The propeller hub 6 has a conventional outer contour which has been modified and adapted to the streamlined shape ofthe toφedo 2 by means of a screwed-on transition ring 5, the after end of which forms one side of the rotation gap 15. The rotation gap 15, as shown in the detailed section, is designed to be conical with the greatest diameter facing abaft. This is to improve the flow conditions over the gap, and also to reduce the effect of any axial deviations between the propeller and toφedo.

The toφedo 2 is divided into three parts, a fixed after part 16 which is designed to have a flange 17 on the upper side for attachment to the rudder hom 3 by means of flange connection 7, and two detachable concentric rings 18, 19 which are held in place by a dog bolt 20. Forward ofthe foremost ring 19 there is a shoulder tuming upon which a ring 21 of tear-resistant material is placed. This ring, as is apparent from the detailed section, is adapted to the rotation gap 15.

The hom bearing boss 22 in the lower hom bearing 8 (Fig. 1) is suspended in a bracket 23 which is structurally integrated into the toφedo 2, i.e., in the toφedo's fixed after part 16.

In order to be able to adjust the clearing ofthe rotation gap simply, the toφedo may to advantage include two rings 18, 19 which are designed to have eccentrically displaced end surfaces, as is shown in Fig. 4, where the eccentricities are indicated with the letter e.

In the perspective view of an arrangement according to the invention in Fig. 5, the design ofthe toφedo has been modified relative to that shown in Figs. 1 and 3, such that the part ofthe toφedo 2 which is in front ofthe rudder hom 3 consists of two semi¬ cylindrical cover plates 25, 26 (shown drawn apart from one another), whose side edges are flanged so that they can be screwed together in a vertical plane running through the axis ofthe propulsion system, and the after end 27 of which (only shown for one cover plate 26) is flanged so that it can be screwed to a corresponding flange in the front edge ofthe after part ofthe toφedo, and the front edge of which is designed to be the after part ofthe rotation gap 15 and forms one ofthe defining surfaces thereof.

Furthermore, it can be seen from Fig. 5 that the rudder ho and the rudder case 3 have the same extemal profile as the rudder blade 4, and that the rudder horn/rudder case 3 is constmcted with a constant cross-section through the skin plate 28 ofthe ship and is secured (welded) thereto and also to the deck 29 in the ship's steering engine room and to vertical braces 30.

The toφedo may have reaction fins. Such reaction fins are known, for example, from NO 154262.

The invention provides an integrated system for the propulsion and steering of a ship. A toφedo is used which is suspended in the rudder hom and cannot be swung relative to the ship. The outer form ofthe toφedo is such that, together with the specially designed propeller hub, it forms an optimised streamlined rotary body. All components in the system interact hydrodynamically and are optimised as a combined unit with a view to propulsion efficiency and manoeuvrability.