The present invention relates to an azimuth propeller apparatus and a ship equipped with the azimuth propeller apparatus.
Generally, ships are equipped with a propeller. The propeller is turned, propelling the ship in a direction that is controlled by a rudder.
FIG. 1 shows a typical conventional ship 80. FIG. 2 is a magnified view of a stern of the ship 80, illustrating a rudder 82 of the ship 80.
As shown in FIGS. 1 and 2, a propeller 81 is provided at the stern, along with the rudder 82. The propeller 81 is driven by the main engine 84 installed in a hull of the ship 80 at the same level. The main engine 84 is has its shaft axially aligned with the propeller 81. The rudder 82 is attached to the stern by a rudder horn 83.
As the main engine 84 drives the propeller 81, the ship 80 is propelled. The direction in which the ship 80 is propelled is controlled by turning the rudder 82 on the rudder horn 83.
In recent years, ships have been proposed, each having an azimuth propeller at the stern. The azimuth propeller can be rotated around a vertical axis. The azimuth propeller propels the ship as it is driven around the horizontal, and steers the ship as it rotates around the vertical axis.
FIG..3 depicts a ship 90 with a conventional azimuth propeller apparatus 91. FIG. 4 is a magnified view of the stern of the ship 90, showing the conventional azimuth propeller apparatus 91.
As shown in FIGS. 3 and 4, the azimuth propeller apparatus 91 comprises a strut 92, a pod 93 and a propeller 94. The strut 92 is connected to the stern of the ship 90 and can rotate around a vertical axis. The pod 93 is secured to the strut 92. The propeller 94 is attached to the pod 93.
In the stern there is provided a generator/engine (G/E), which is located above the strut 92. The generator/engine drives a generator (not shown), which generates electric power. The electric power is supplied to the motor provided in the pod 93. Driven with the electric power, the motor drives the propeller 94.
FIG. 5 is a graph representing the various relations between the rudder angle and the lateral force, which are observed with various ships. In FIG. 5, curve D indicates the angle-force relation observed when the propeller 81 and the rudder 82 (both shown in FIG. 2) are used, propelling and steering the ship 80 shown in FIG. 1 at low speed of 18 knots. Curve E shows the angle-force relation observed when the azimuth propeller apparatus 91 (shown in FIG. 4) is used, propelling and steering the ship 90 shown in FIG. 3 at low speed of 18 knots. Curve C indicates the angle-force relation observed when the ship 80 is propelled and steered at high speed of 25 knots.
As can be understood from curve C, the ship 80 can receive a sufficient lateral force while being propelled at a relatively high speed, as in off-shore navigation. The ship 80 can therefore be well steered in off-shore navigation. However, when the ship 80 is propelled at low speed as it is navigated in the harbor, as it is moored at the pier, or as it leaves the pier, its steerability greatly decreases as curve D reveals in FIG. 5.
As described above, the ship 90 shown in FIG. 3 has the azimuth propeller apparatus 91 shown in FIG. 4. As the strut 92 of the apparatus 91 is rotated, a lateral force is applied to the ship 90. The lateral force is smaller than the lateral force applied to the ship 80 (FIG. 1) as the rudder 82 is rotated. Therefore, the greater part of the lateral force, which is applied to the ship 90 when the ship 90 is propelled at low speed, is a lateral component of the propelling force that the propeller 94 applies to the ship 90.
The lateral component of the propelling force applied to the ship 90 at low speed of 18 knots is small as is indicated by curve E in FIG. 5. In other words, the steerability of the ship 90 equipped with the azimuth propeller apparatus 91 also become insufficient during the low-speed navigation.
To impart sufficient steerability to the ship 91, a sufficiently large lateral force must be applied to the ship 91, not only when the ship 91 is propelled at low speed, but also when the wind is strong or waves are high.
If tax is levied on carbon emission in order to prevent the global warming, ships will need to be navigated at low speed to save energy. When ships are navigated at low speed, however, the rudder force decreases. Hence, the steerability of a low-speed ship is particularly lowered.
It is therefore demanded not only that a ship with an azimuth propeller apparatus maintains sufficient steerability even while navigated at low speed, but also that the propelling efficiency of azimuth propeller apparatuses be enhanced.
GB 1 203 560 discloses a steering and propulsion gear for ships and relates to marine propulsion drive rather then to an azimuth propeller apparatus shape like flap and arranged at the back of a skeg protruding from the stern of a ship, and which therefor has a rudder that conforms to the skeg in shape.
The present invention has been made to solve the problems described above. An object of the invention is to provide an azimuth propeller apparatus which can increase the steerability of ships during low-speed navigation and which can propel ships with high efficiency. Another object of the invention is to provide a ship which is equipped with this azimuth propeller apparatus.
According to the invention, there is provided an azimuth propeller apparatus which comprises: a rotatable shaft connectable to a stern of a ship and comprising a skeg protruding from the stern of the ship and having a notch in an edge part to allow passage of the propeller being rotated around the shaft; a rudder plate secured to the shaft configured control the course of the ship, a pod mounted on middle part of the rudder plate; a propeller having a propeller shaft connected to one end of the pod; and driver provided in the pod, for driving the propeller shaft. In a preffered embodiment, the rudder plate includes an upper rudder plate secured to upper part of the shaft which is located above the pod and configured to control the course of the ship and a lower rudder plate secured to under part of the shaft which is located below the pod and configured to control the course of the ship.
According to the present invention, there is also provided a ship which comprises the aforementioned azimuth propeller apparatus.
In another preferred embodiment, a reaction fin is connected to the pod and located at fore-flow of the propeller and swirl water in a direction opposite to a rotational direction of the propeller.
Further preferred embodiments are described in the subclaims.
The invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:
The embodiments of the invention will be described, with reference to the accompanying drawings.
FIG. 5 is a graph representing the various relations between the rudder angle and the lateral force, which are observed with various ships. Curve D indicates the angle-force relation observed when the propeller 81 and the rudder 82 (both shown in FIG. 2) are used, propelling and steering the ship 80 shown in FIG. 1 at low speed of 18 knots. Curve E shows the angle-force relation observed when the azimuth propeller apparatus 91 (shown in FIG. 4) is used, propelling and steering the ship 90 shown in FIG. 3 at low speed of 18 knots. Curve A indicates the angle-force relation observed when the azimuth propeller apparatus 1 (shown in FIG.4) is used, propelling and steering a ship at low speed of 18 knots.
As seen from curve A, the lateral force is almost equal to the sum of the lateral force applied to the hull when the propeller 81 and the rudder 82 (FIG. 2) are used and the lateral force applied to the hull when the azimuth propeller apparatus 91 (FIG. 4) is used. Obviously, the ship with the azimuth propeller apparatus 91 according to the invention (Embodiment 4) can acquire a larger lateral force than the ship 80 with the propeller 81 and rudder 82 and the ship 90 with the conventional azimuth propeller apparatus 91.
Curve B in FIG. 5 indicates the relation between the rudder angle and the lateral force, angle-force relation observed when the ship according to the second embodiment is propelled and steered at low speed of 18 knots. As can be evidenced by comparing curve B with curve A, the lateral force is larger than the literal force applied to the ship according to the first embodiment.
Moreover, curve C in FIG. 5 indicates the angle-force relation observed when the ship 80 is propelled and steered at high speed of 25 knots. As can been seen from comparison between curve C and curve B, a lateral force, which is comparable with the lateral force applied to the ship 80 navigated at 25 knots, can be applied to the ship, according to the second embodiment, though the ship is navigated at low speed of 18 knots.
The azimuth propeller apparatus according to this invention is characterized in two respects. First , the gap between the rudder plate and the hull is narrow, increasing the steerability of the ship. Second, the azimuth propeller apparatus is rotated by 180° from the normal position to propel the ship backward.
FIG. 7 is a side view of the stern of the ship according to the embodiment. With reference to FIG. 7 the azimuth propeller apparatus 4 and skeg 51 of the embodiment will be described.
The azimuth propeller apparatus 4 has a rudder plate 53. The rudder plate 53 is a modification of the rudder plate 23 shown in FIGS. 5 and 9. The rudder plate 53 has a projection 531 on the front edge and can rotate through 360°. The rudder plate 53 is identical to the rudder plate 23 of the azimuth propeller apparatuses 1 and 2 in the shape of its cross section, as is indicated by the two-dot, dashed lines 531 in FIG. 7.
The skeg 51 has a U-notch 511 in the rear edge. It is in the notch 511 in which the projection 531 of the rudder plate 53 is placed as long as the rudder plate 53 remains in the normal position. Thus, the gap between the plate 53 and the hull is much narrower than in the case of the conventional ships.
To propel the ship backward, it suffices to rotate the shaft 20 by 180°, thereby setting the rudder plate 53 in the position shown in FIG. 8. The propeller 21 is then located in the notch 511 of the skeg 51. As the propeller 21 is rotated in the notch 511, it applies a backward propelling force to the hull.
FIG. 9 shows a modification of the azimuth propeller apparatus 4 which has a reaction fin 50 at the fore-stream of the propeller 21.
The use of the reaction fin 50 can help to increase the ship-propelling efficiency.