Generally, in the stern section of the marine craft, lubrication oil, felt gaskets against oil leakage, balls for the bearing of the shaft, spider balls for directing the power, and fastening elements such as bellows, bolts and clamps that provide the inter connection of these components, gear assemblies and joints are employed.

In US Patent No. 5066255, as a document known from the state of art, a drive arrangement in which a drive shaft extends from an inboard engine through the stern wall to a propeller arranged in a tunnel-shaped water flow guide structure extending backwardly from the bottom edge of the stern wall, is described. Said structure is movable upwards and downwards as well as to the left and to the right. However the number of the components providing these movements is quite high and furthermore balls, spider, felt, gear wheels and lubrication oil are used, consequently the ratio of break-down and damages increases due to the mechanical wearing of said components.

The object of the present invention is the realisation of the stern unit in marine craft, whereby power generated by the engine and the transmission mechanism is linearly transmitted to the propeller by means of a shaft.

Another object of the present invention is to increase the manoeuvrability of the marine craft by directing/orienting it without blocking the water stream.

The stern unit for marine craft, realized in order to attain the object of the present invention, has been illustrated in the attached drawings; wherein:

Figure 1, is the cross sectional view of the stern unit, Figure 2, is the plan view of the stern unit.

The components shown in the figures are individually enumerated as follows: 1. Stern unit 2. Casing 3. Shaft 4. Shaft housing 5. Water lubricated bearings 6. Propeller 7. Rudders 8. Rudder stand 9. Transmission element 10. Hydraulic piston 11. Flange 12. Rear bottom edge of the hull The stern unit (1) provides the movement and while having way, the guidance and direction of the marine craft.

The stern unit (1) comprises a casing (2), a shaft (3), a shaft housing (4), water lubricated bearings (5), propeller (6), rudder (7), a rudder-stand (8) and a hydraulic piston (10). The stern unit (1) contains a fish-back shaped casing (2) serving as a tunnel and a propeller (6) near the outlet of said casing (2).

The propeller (6) is connected to the inboard engine mounted in the marine craft in a straight line, by means of the transmission mechanism using a shaft (3), borne in the shaft bearing (4) and water bearings (5) without using any spiders and balls. The rudders activated by means of a hydraulic piston takes place in front of the propeller enable the marine craft to be guided.

The casing (2) that protects the propeller and is used to orient the water, consists of two sections that are open at the bottom, namely; an inlet and an outlet section. The inlet section is a narrow section where the stern unit (1) is connected to the transom of the hull (12). Said stern unit (1) is fixed to the rear wall of the hull (12) by means of a flange (11) over the inlet section ; whereas the outlet section, being an extension of the inlet section, has a fish-back shaped curved structure that expands towards the end portion. The bottom surface of said casing (2) has a parabolic shape. However the upper section of one arm of the parabole, which is the nearest to the rear of the marine craft (12) has an inclined structure and during the motion of the marine craft, the water stream passing below the marine craft first strikes to this inclined surface which is at the bottom surface of the casing (2). Due to the difference of height between the lower line of the marine craft and said inclined surface provided on the lower surface of the casing (2) which is placed at a higher level, withdrawal of air from the water surface line towards the surface of the casing (2) is enabled.

In this case, water and air mix together at the peak point of the lower surface of the casing (2) which has a parabolic structure and by providing an air bed, friction between the casing (2) and the water is thus minimized without any air ingestion by the water stream passing through the propeller. Furthermore, a hydraulic piston (10) is provided at the upper side of the casing (2) to enable the steering (7) to move and the rudder stand (8) is provided at the down stream of the casing (2).

The torque and the trust obtained from the inboard engine and the transmission mechanism., are linearly transmitted to the shaft (3) by using an elastic transmission element (9).

In this case, the force and movement obtained from the inboard engine and the transmission mechanism, are linearly transmitted to the propeller (6) mounted at the end of the shaft (3) without any energy loss. Said shaft (3) is placed in the casing (2), between the water bearings (5) preferably made of rubber, that surround the shaft (3) and which are placed in the tube formed shaft housing (4) in the casing (2) so that preferably one is provided at the front and one at the back side.

Water taken in for cooling the engine is transmitted to the shaft housing (4) wherein the shaft (3) is placed between the water bearings (5), by means of a pump and a valve, in order to form a thin layer of water between the shaft (3) and the water bearings (5) and the shaft housing (4). Formation of such a layer of water, cools the shaft (3) and minimizes the friction between the shaft (3) and the water bearings (5).

Preferably two rudders (7) which are activated by means of a hydraulic piston (10) placed above the casing (2), are located in front of the propeller (6).

Said rudders (7) are placed in the rudder stands (8) located above the casing (2), in such a manner that a certain distance is kept between them. Said rudders (7) move around the axis of said rudder stands (8). By using two rudders (7), a channel wherein the water stream created by the propeller (6) is formed and the water stream is oriented without blocking its flow. By means of said rudders (7) which are simultaneously oriented to the same direction by the hydraulic piston (10), the direction of water stream while flowing from said channel is changed which also changes the direction of the boat.

In the stern unit (1) according to the present invention, the components used in other stern units, such as lubrication, felts against oil leakage, balls used in shaft bearings (3), spider balls used to direct the power and in association with

these, the supplementary fastening elements such as the bellow, bolts and clamps, gear assemblies and joints, are not used.

In addition to the linear transmission of the engine power to the propeller (6) and water without any loss of energy, the number of operating components is minimized, thus reducing the potential of break-down and damage to a minimum level. Furthermore, the maintenance intervals are guide long due to the fact that the number of components is less and no mechanical wearing is observed ; and as no balls are used in the stern unit (1), it operates with less noise and without any vibrations, as compared to other stern units.