ATBECHDEDKESFRGBGRITLILUNLSEMCPTIESILTLVFIROMKCYALTRBGCZEEHUPLSK..HRIS..MTNORS..SM..................
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DIM360 Ver 2.40 (30 Jan 2013) - 1100000/0
2692630
EUROPEAN PATENT APPLICATION
published in accordance with Art. 153(4) EPC
A1
20140205
EP
12764722.0
20120327
20130913
ja
en
en
2011072206
20110329
JP
20140205
201406
20140205
201406
B63H 25/42 20060101AFI20121019BHEP
de
HEBETRIEBWERKVORRICHTUNG
en
ELEVATION-TYPE THRUSTER APPARATUS
fr
PROPULSEUR DU TYPE RELEVABLE
2
Kawasaki Jukogyo Kabushiki Kaisha
101096636
38.117939
1-1, Higashikawasaki-cho 3-chome Chuo-ku
Kobe-shi, Hyogo 650-8670
JP
ONODA, Kenichi
c/o Kawasaki Marine Engineering Co., Ltd. 1-1, Higashikawasaki-cho 3-chome Chuo-ku Kobe-shi
Hyogo 650-8670
JP
ONODERA, Tatsuya
c/o Kawasaki Marine Engineering Co., Ltd. 1-1, Higashikawasaki-cho 3-chome Chuo-ku Kobe-shi
Hyogo 650-8670
JP
Piésold, Alexander James
100027770
Dehns St Bride's House 10 Salisbury Square
London EC4Y 8JD
GB
AL
AT
BE
BG
CH
CY
CZ
DE
DK
EE
ES
FI
FR
GB
GR
HR
HU
IE
IS
IT
LI
LT
LU
LV
MC
MK
MT
NL
NO
PL
PT
RO
RS
SE
SI
SK
SM
TR
JP2012002101
20120327
ja
WO2012132400
20121004
201240
A vertically movable thruster apparatus includes: a pair of racks (31) of required length which are disposed, respectively, on outer surfaces of a canister (21) and each of which has tooth sections (32) of constant pitch in the vertical direction; guide members (40) which are disposed along the racks (31), respectively; and a pair of elevation devices (30) for vertical movement of the canister (21) in a vertical passageway (2). Each of the pair of the elevation devices (30) includes: a pair of upper and lower catches (36), (38) which are respectively independently brought into fitting engagement and disengagement with tooth sections (32) at positions vertically spaced apart; a pair of upper and lower frames (34), (35) equipped with the catch (36) and the catch (38), respectively; and an elevation cylinder (33) arranged between the frames (34), (35). The elevation cylinder (33) is configured such that, with respect to one of the frames (34) firmly fastened to the vertical passageway, the elevation cylinder moves the other frame (35) vertically using the guide member (40) as a guide. According to this construction, the thruster can be raised to a position above a waterline.

Technical Field
The present invention relates to a vertically movable thruster apparatus (up-down type) which incorporates therein a thruster for use to hold in a fixed position a drill ship, a floating production facility or the like.

Background Art
Heretofore, the exploration for sea bottom oil and gas field has been performed in offshore areas located away from the land. In recent years, such sea bottom oil and gas field exploration tends to proceed into further greater water depths. In the case of drill ships, floating production facilities and so on (hereinafter, collectively referred to as the "drill ship or the like") which are used in the exploration in areas of greater water depth, drilling of the sea bottom by the drill ship or the like takes place several thousand meters below the sea surface. Therefore, the drill ship or the like is adapted to be held in a fixed position over sea without having to be anchored to the sea bottom. As a system that holds the drill ship or the like in a fixed position over sea, systems equipped with a plurality of thrusters for performing attitude control have been used more and more. In such a drill ship or the like equipped with the plurality of thrusters, it is possible to control, for example, a thrust force or the like of each thruster so that, even under a heavy weather, the drill ship or the like can be held in a fixed position by making use of, for example, GPS signals. For example, in the case of the drill ship, there are provided four to six thrusters so as to provide holding thereof in a fixed position.
However, the thruster may fail to operate properly due to long-term use or may need unexpected maintenance. However, during operation of the drill ship or the like, the drill ship or the like is not allowed to leave the fixed position because, for example, the state of drilling of the sea bottom by an excavation drill must be maintained. Therefore, if inspection and repair are required for a thruster, this will give rise to, for example, underwater removal of the thruster by divers, which is carried out with difficulty. Moreover, during heavy weather season, it is also impossible to detach the thruster. Therefore, the timing when to carry out a repair work is also restricted.
It is also conceivable to move the drill ship or the like to a dock on land for inspection and repair. This, however, is costly and time-consuming.
Accordingly, in recent years, there has been proposed an apparatus capable of moving upward (raising), even at an offshore operation site, a thruster to a position above the waterline to enable inspection and repair work.
For example, as a prior art of this kind, there is a vessel characterized in that the thruster is moved vertically by a rack and pinion drive system or by a hydraulic cylinder drive system. In the rack and pinion drive system, the pinion is provided on the thruster, and the rack on the side of the ship's hull is allowed to extend upward, whereby the thruster can be moved upward beyond the waterline along the rack by the pinion. In the hydraulic cylinder drive system, an elevation (up-down) cylinder is suspended under the deck and an elevation (up-down) body is moved upward and downward by the elevation cylinder (for example, see Patent Literature 1).
Further, as another prior art, there is proposed a technique that moves a thruster vertically using a hydraulic cylinder drive system or a rack and pinion drive system. This prior art describes, as the hydraulic cylinder drive system, a one-step push-up system and a one-step push-up telescopic system, and also describes, as the rack and pinion drive system, a system for moving the rack on the side of the thruster upward and downward in a single step using the pinion provided on the ship's hull and a system for moving the rack upward and downward using a different pinion in the middle of vertical (up-down) movement. By these systems, the thruster is made movable upward and downward between a position below the ship's bottom and a position above the deck (see, for example, Patent Literature 2).

Citation List

Patent Literature
- Patent Literature 1: Japanese Patent No. 4526184
- Patent Literature 2: JP 2001-55197 A

Summary of Invention

Technical Problem
However, Patent Literature 1 requires a large-size drive device capable of moving a large load upward and downward in order that the thruster is moved upward and downward by the rack and pinion drive system. In addition, in order to attain compactness of the drive device, it is necessary to use high-strength materials for both the rack and the pinion. Besides, a reduction gear mechanism is a machine-finished product, which means that the elevation device is costly.
In the case of the rack and pinion drive system set forth in Patent Literature 2, the elevation device also costs considerably, as in Patent Literature 1.
Besides, according to the one-step push-up hydraulic cylinder system of Patent Literature 2, the push-up length, for which the thruster is required to be moved upward, is accomplished by a single step of the hydraulic cylinder. Thus, the stroke of the hydraulic cylinder required to make becomes long. Further, the thruster of a great weight is moved upward and downward above the waterline, therefore requiring a considerably large-scale device in order to have sufficient buckling strength. This costs considerably. Furthermore, in the case of the one-step push-up telescopic hydraulic cylinder system, the telescopic type rod is sequentially extended and contracted so that the thruster is moved upward (downward) for a required upward movement (downward movement) length. This makes the cylinder complicated in structure. Moreover, similar to the hydraulic cylinder, a considerably large-scale device is required for sufficient buckling strength, which will cost considerably.
Further, in the hydraulic cylinder system of Patent Literature 1, the upward and downward movement is performed via a ring surrounding the elevation body of the thruster. Therefore, if the thruster increases in size thereby causing the cross-section of the elevation body to increase, this also causes the ring surrounding the elevation body to increase in size. Under the circumstances, it is difficult to address the increase in the size of the elevation device.

Solution to Problem
Accordingly, an object of the present invention is to provide a vertically movable thruster apparatus including a compact elevation device, which is capable of raising a thruster to a position above a waterline for inspection and repair even at an offshore operation site.
In order to achieve this object, the present invention provides a vertically movable thruster apparatus, including a thruster disposed so as to project downward from a bottom thereof, and a canister which incorporates therein a drive device for driving the thruster and is vertically movable in a vertical passageway provided in a ship's hull, the vertically movable thruster apparatus comprising: at least one pair of racks of required length which are disposed in respective positions of outer surfaces of the canister that are opposite each other in a horizontal direction and each of which has tooth sections of constant pitch in a vertical direction; guide members which are vertically disposed along the racks, respectively; and one pair of elevation devices for bringing the canister into vertical movement between an operative position of the thruster and a position above a waterline along the one pair of racks in the vertical passageway, wherein each of the one pair of elevation devices includes: a pair of upper and lower catches which are independently brought into fitting engagement and disengagement with respective tooth sections in positions vertically spaced apart in the rack; a pair of upper and lower frames including the upper and lower catches, respectively; and elevation cylinders each of which is disposed between the pair of upper and lower frames, and each of the elevation cylinders is configured such that, with respect to one of the frames that is firmly fastened to the vertical passageway, the elevation cylinder moves the other frame vertically using the guide member as a guide. The terms "ship's hull" mentioned in this specification and in the claims refers to an object which includes a drill ship, a floating production facility, etc., and into which a vertically movable thruster apparatus is incorporated. The term "canister" refers to a tubular container from which bottom a thruster projects downward and which incorporates therein a drive device adapted to drive the thruster.
According to this configuration, with one of the catches brought into fitting engagement with a tooth section of the rack provided in the canister, the catch is moved upward by the elevation cylinder. Thereafter, the other catch is brought into fitting engagement with a tooth section of the rack thereby to support the load of the vertically movable thruster apparatus, and the one catch is disengaged from the tooth section and then moved downward by the elevation cylinder so as to be brought into fitting engagement with a lower tooth section. Thereafter, the other catch is disengaged from the tooth section, and the one catch is moved upward by the elevation cylinder. In other words, by repetition of a so-called inchworm motion, it becomes possible to stably move upward the vertically movable thruster apparatus by the compact elevation device including the elevation cylinder of a short stroke. By reversing the operations described above, downward movement occurs stably. Therefore, the compact elevation device can move the vertically movable thruster apparatus vertically between an operative position and a position above a waterline. Moreover, since each of the elevation devices is independently provided for each of the pair of the racks, this configuration makes it possible that an increase in the cross-section of the canister associated with an increase in size of the thruster can easily be addressed without an increase in size of the frames of the elevation device.
The pair of upper and lower frames may be mounted such that the lower frame is firmly fastened to the vertical passageway. This configuration makes it possible to move the vertically movable thruster apparatus upward and downward while its own weight is being supported on the bore side of a larger area of the elevation cylinder disposed between the pair of upper and lower frames, and hence the elevation cylinder can be used in optimal design.
The vertical passageway may include a maintenance and inspection floor in a position above a waterline, and the canister may include racks of required length for upward movement of the thruster to the position of the maintenance and inspection floor, and each of the elevation devices may be disposed in a position of required height in the vertical passageway so that the thruster is movable upward from its operative position to the position of the maintenance and inspection floor. This configuration makes it possible to move the thruster upward and downward from the operative position to position of the maintenance and inspection floor where the thruster can be maintained. Thus, the thruster can be detached from the canister on the maintenance and inspection floor and maintenance and inspection of the thruster can be carried out there.
The pair of upper and lower frames may include: drive cylinders for independently bringing the catches into fitting engagement and disengagement with the rack in an upper position and in a lower position, respectively; and guide sections for bringing the catches into fitting engagement and disengagement with respective tooth sections of the rack by extending and contracting motions of the drive cylinders. Thus, with a compact configuration, it becomes possible to bring the catches into fitting engagement and disengagement with the tooth sections of the racks from the frames arranged respectively in upper and lower positions of the elevation cylinder.
Each of the elevation cylinders may be configured such that, during operation of the thruster, the elevation cylinder brings the pair of upper and lower catches into fitting engagement with respective tooth sections of the rack to exert forces of opposite vertical directions on the catches thereby to hold a vertical load acting against the canister. According to this configuration, there is provided a method of holding the load acting against the canister, in which forces in opposite directions are exerted on the pair of catches, and thereby a vertical static load acting against the canister is held by the catches provided in the frames which are firmly fastened to the vertical passageway while a dynamic load acting against the canister in an opposite direction relative to the static load due to ocean waves or the like is held by the catches provided in the elevatable frames.
The vertical passageway may include fixing sections for the elevation device which are arranged in a plurality of positions vertically spaced apart; and a load holding device for temporarily holding the load of the vertically movable thruster apparatus when effecting a change of the fixing sections, and the elevation device may include fastening means detachable to the fixing sections of the vertical passageway. According to this configuration, during vertical movement of the vertically movable thruster apparatus, the fixing sections for the elevation device are changed, with the load of the vertically movable thruster apparatus being temporarily held by the load holding device in an intermediate portion of the vertical passageway. As a result, it is possible to secure a distance for which the vertically movable thruster apparatus can be moved upward and downward while suppressing an increase in rack length.
The vertical passageway may include: a support guide for supporting a horizontal force acting against the canister; and an enclosing plate which reduces in a position of the support guide, a spacing between the canister and the vertical passageway over an entire circumference. According to this configuration, it becomes possible to suppress a fluctuation of water surface between the vertical passageway and the canister due to ocean waves on the water.
The vertically movable thruster apparatus may comprise a jack for supporting the canister in a horizontal direction, between the support guide and the canister. According to this configuration, it becomes possible to easily prevent an unstable motion of the canister due to a clearance gap defined between the canister and the vertical passageway during operation of the thruster.

Advantageous Effects of Invention
According to the present invention, there is provided a vertically movable thruster apparatus including a compact elevation device capable of moving a thruster vertically so that the thruster is raised to a position above the waterline even at an offshore operation site for inspection and repair.

Brief Description of Drawings
- FIG. 1 is a side view of a vertically movable thruster apparatus according to an embodiment of the present invention;
- FIG. 2 is a front view of the vertically movable thruster apparatus shown in FIG. 1;
- FIG. 3 is an enlarged cross-sectional view taken along the lines III-III and looking in the direction of the arrows shown in FIG. 1;
- FIG. 4 is an enlarged cross-sectional view taken along the lines IV-IV and looking in the direction of the arrows shown in FIG. 1;
- FIG. 5 is an enlarged cross-sectional view taken along the lines V-V and looking in the direction of the arrows shown in FIG. 1;
- FIG. 6 is an enlarged view of a part (VI) shown in FIG. 5;
- FIG. 7 is an enlarged cross-sectional view taken along the lines VII-VII and looking in the direction of the arrows shown in FIG. 1;
- FIG. 8 is an enlarged view of a section of the elevation device shown in FIG. 2;
- FIG. 9 is a cross-sectional view taken along the lines IX-IX and looking in the direction of the arrows shown in FIG. 8;
- FIG. 10 is a cross-sectional view taken along the lines X-X and looking in the direction of the arrows shown in FIG. 9;
- FIG. 11 is a cross-sectional view taken along the lines XI-XI and looking in the direction of the arrows shown in FIG. 9;
- FIG. 12 comprised of (a) through (i), represents an upward movement, with a positive downward load acting against catches;
- FIG. 13 comprised of (a) through (i), represents a downward movement, with a positive downward load acting against the catches;
- FIG. 14 comprised of (a) through (i), represents an upward movement, with a negative upward load acting against the catches;
- FIG. 15 comprised of (a) through (i), represents a downward movement, with a negative upward load acting against the catches;
- FIG. 16A and FIG. 16B are side views depicting an upward movement of the vertically movable thruster apparatus according to the first embodiment;
- FIG. 17A and FIG. 17B are side views depicting an upward movement, subsequent to the upward movement of FIGS. 16A, 16B, of the vertically movable thruster apparatus according to the first embodiment;
- FIG. 18A and FIG. 18B are side views depicting an upward movement of a vertically movable thruster apparatus according to a second embodiment;
- FIG. 19A and FIG. 19B are side views depicting an upward movement, subsequent to the upward movement of FIGS. 18A, 18B, of the vertically movable thruster apparatus according to the second embodiment;
- FIG. 20A and FIG. 20B are side views depicting an upward movement, subsequent to the upward movement of FIGS. 19A, 19B, of the vertically movable thruster apparatus according to the second embodiment;
- FIG. 21A and FIG. 21B are side views depicting an upward movement, subsequent to the upward movement of FIGS. 20A, 20B, of the vertically movable thruster apparatus according to the second embodiment;
- FIG. 22 is a front view illustrating a catch versus rack relationship according to a first example of the measures against ocean waves in a vertically movable thruster apparatus according to the present invention; and
- FIG. 23 is a front view illustrating a catch versus rack relationship according to a second example of the measures against ocean waves in a vertically movable thruster apparatus according to the present invention.

Description of Embodiments
Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawing figures. In the following embodiments, a description will be given taking, as an example, a vertically movable thruster apparatus installed in a ship.
As shown in FIGS. 1, 2, a vertically movable thruster apparatus 20 includes a canister 21 adapted to move upward and downward in a vertical passageway 2 provided in a ship's hull 1, and a thruster 22 which projects downward from the lower side of the canister 21. The vertical passageway 2 and the canister 21 are configured such that they have a rectangular cross section in planer view (see FIGS, 4, 5). Defined between the canister 21 and the vertical passageway 2 are predetermined spacings S1, S2. Of these spacings S1, S2, the one on the side of a rack 31 to be described later, i.e., the spacing S2, is wider than the other.
The canister 21 contains therein a pivoting drive unit 23 for steering the thruster 22, a drive motor 25 for rotating a propeller 24, a steering pump unit 26 for supplying a drive oil to the steering drive unit 23 and a lubricating oil pump unit 27 for lubricating each component.
A pair of racks 31 are arranged, respectively, on two opposing outer surfaces of the canister 21. In each of the racks 31, tooth sections 32 are formed at a constant pitch in the vertical direction, and the racks 31 are arranged continuously in the vertical direction of the canister 21. Diagrammatic representation of the tooth sections 32 located in the middle of the rack 31 is omitted in the figure. Portions of the opposing racks 31, which project outward from the canister 21, are coupled to each other by a reinforcing member 31b.
In addition, the vertical passageway 2 along which the canister 21 moves upward and downward is provided with support guides 3 for supporting a horizontal load acting against the canister 21 during operation of the thruster 22, support and vertical-movement guides 4 for supporting a horizontal load acting against the canister 21 and for guiding the canister 21 during vertical movement of the canister 21 and vertical-movement guides 5 which serve as a guide during vertical movement of the canister 21. In this example, the support guides 3 are disposed at the bottom, and the support and vertical-movement guides 4 are provided at two different vertical locations above the support guide 3. Further, the vertical-movement guide 5 is disposed in the upper portion of the vertical passageway 2, which lies above the canister 21 when the thruster 22 is in operation and which serves as a guide when the vertically movable thruster apparatus 20 is moving upward and downward.
Disposed between the canister 21 and the vertical passageway 2 of the ship's hull 1 are a pair of elevation devices 30 for moving the canister 21 upward and downward along the vertical passageway 2 so that the thruster 22 is moved upward and downward.
Each of the elevation devices 30 is provided with an elevation cylinder 33 which is disposed at the position of the rack 31 and which moves the canister 21 upward and downward via the rack 31. The lower part of the elevation cylinder 33 is supported on the vertical passageway 2, while the upper part thereof is supported on the canister 21. How the elevation cylinder 33 is supported and how the canister 21 is moved upward and downward by the elevation device 30 will be described later.
Referring to a cross-section taken in a position above the canister 21 (see FIG. 3), the racks 31, disposed on two opposing outer surfaces of the canister 21, project outward. The racks 31 are formed so as to have a required length extending in the vertical direction (see FIG. 1). Via the racks 31, the load of the vertically movable thruster apparatus 20 is supported on the ship's hull 1 by the elevation devices 30. In this example, the racks 31 are arranged on the two opposing surfaces of the canister 21. However, the racks 31 may be arranged at positions in a diagonal relationship.
Referring to a cross-section taken in the lower position of the elevation device 30 above the canister 21 (see FIG. 4), the canister 21 is guided by vertical-movement guides 5 which are disposed at four corners of the vertical passageway 2. Besides, in the present embodiment, there are disposed, in this lower position, load support structures (fixing sections) 9 for supporting the load of the elevation devices 30.
Referring to a cross-section of the canister 21 taken in the position of the support and vertical-movement guides 4 (see FIG. 5), the canister 21 is supported by the support and vertical-movement guides 4 arranged at four corners of the vertical passageway 2. As shown in FIG. 6, each of the support and vertical-movement guides 4 is comprised of a support guide section 4a for supporting a horizontal load acting against the canister 21 and a vertical-movement guide section 4b for guiding the canister 21 when the canister 21 is being moved upward and downward. The vertical-movement guide section 4b is arranged at a corner so as to lie on an extension of each of the vertical-movement guides 5, while the support guide section 4a is disposed on the inner side thereof. The canister 21 is provided, at its position against which the support guide section 4a abuts, with a pad 6 (see FIGS. 1, 2). A clearance gap defined between the support guide section 4a and the pad 6 is smaller, while a clearance gap defined between the vertical-movement guide section 4b and the canister 21 is made slightly greater. In addition, it is set such that a clearance gap T defined between the pad 6 and the support guide section 4a allows for vertical movement of the canister 21, but should be small enough to minimize horizontal movement of the canister 21 (for example, about several millimeters although it is represented in an exaggerated manner in the figure).
Referring to a cross-section of the canister 21 taken in the bottom position thereof (see FIG. 7), the canister 21 is supported horizontally by the support guides 3 arranged at four corners of the vertical passageway 2. The support guides 3 are disposed so as to lie on downward extensions of the support guide sections 4a provided in the support and vertical-movement guides 4, respectively.
In addition, according to the present embodiment, there are disposed, in the upper portions of the support guides 3, enclosing plates 7 that reduce the spacings S1, S2 defined between the periphery of the canister 21 and the vertical passageway 2 into a smaller spacing S3 as shown in FIG. 7. The enclosing plates 7 are provided such that the spacing around the canister 21 becomes a specified smaller spacing, i.e., the spacing S3. As will be described later, the fluctuation of water surface between the vertical passageway 2 and the canister 21 due to ocean waves on the water is suppressed by a throttle effect of the spacing S3. In this example, the enclosing plates 7 are mounted in the support guides 3 located at the bottom and in the support and vertical-movement guides 4 on the lower side (see FIGS. 1, 2).
In addition, the clearance gap T (see FIG. 6) is defined between the support guides 3 and the outer surface of the canister 21 and between the support guide sections 4a of the support and vertical-movement guides 4 and the outer surface of the canister 21. Because of this, during operation of the thruster 22, the canister 21 moves for a distance corresponding to the clearance gap T. In order to prevent such motion of the canister 21, jacks 8 may be provided near the level of the support guides 3 at the lower portion of the canister 21 in operation (see FIG. 1). If jacks 8 are provided, for example, in the positions of the support and vertical-movement guides 4 located above (these jacks are not shown), that is, two jacks 8 are provided on each surface, i.e., eight jacks 8 in total, are provided, it is possible to stably hold the canister 21.
Next, as shown in FIG. 8, each of the elevation devices 30 has a lower frame 34 for supporting, on the side of the vertical passageway 2, the lower part of the elevation cylinder 33, which lower frame is hereinafter referred to as the "HC (holding catch) frame 34", and an upper frame 35 which is disposed at the upper portion of the elevation cylinder 33 and which is moved upward and downward, which upper frame is hereinafter referred to as the "WC (working catch) frame 35". This WC frame 35 is supported on the side of the canister 21. In addition, each of the elevation cylinders 33 is connected to the HC frame 34 and to the WC frame 35 by pins 33a such that the elevation cylinder 33 is bendable around the pins 33a.
The HC frame 34 incorporates (is equipped with) a holding catch 36 (locking piece)36 (hereinafter referred to as the "HC" 36) which can be brought into fitting engagement with the tooth section 32 of the rack 31 (including fitting engagement with a gap), and there is disposed, in a direction counter to the rack 31, a holding catch drive cylinder 37 (hereinafter referred to as the "HC" cylinder 37) for moving the HC 36 horizontally. The WC frame 35 incorporates (is equipped with) a working catch 38 (locking piece) 38 (hereinafter referred to as the "WC" 38), and there is disposed, in a direction counter to the rack 31, a working catch drive cylinder 39 (hereinafter referred to as the "WC" cylinder 39) for moving the WC 38 horizontally. The HC cylinder 37 and the WC cylinder 39 are alternately independently driven and controlled as will be described below.
As shown in FIG. 9, the elevation cylinders 33 are disposed across the rack 31 on both right and left sides. Likewise, the WC frames 35 provided at the upper portions of the elevation cylinders 33 are provided across the rack 31, while the WC frames 34 provided at the lower portions of the elevation cylinders 33 are provided across the rack 31. The HC 36 and the WC 38 adapted to move backward and forward from each of the HC frames 34 and each of the WC frames 35 toward the rack 31 are formed of thick plates such that portions fittingly engaged with the tooth portions of the rack 31 are higher and portions at widthwise both ends which move along the HC frame 34 and the WC frame 35 are lower. The WC 38 and the HC 36 are formed so as to have a thickness capable of supporting not only a load during vertical movement of the vertically movable thruster apparatus 20 but also a vertical load acting against the vertically movable thruster apparatus 20 during operation.
Further, the HC 36 moves backward and forward along a guide section 34a provided in the HC frame 34, while the WC 38 moves backward and forward along a guide section 35a provided in the WC frame 35. Fitting engagement and disengagement of the HC 36 with the rack 31 is achieved by the HC cylinder 37 disposed in the HC frame 34. Fitting engagement and disengagement of the WC 38 with the rack 31 is achieved by the WC cylinder 39 disposed in the WC frame 35. The HC frame 34 is firmly fastened to the load support structure 9 provided in the vertical passageway 2 on the side of the ship's hull 1 across the rack 31. The firm fastening of the HC frame 34 to the load support structure 9 is provided by welding, or by pin joint mounting, bolt mounting or the like, to enable detachable mounting.
As shown in FIG. 10, each of the HC frames 34 disposed across the rack 31 has guide section 34a for guidance of the HC 36, and fitting engagement and disengagement of the HC 36 with the rack 31 is accomplished by the HC cylinder 37 disposed in a direction counter to the rack 31.
In addition, as shown in FIG. 11, the WC frames 35 are also disposed across the rack 31 in the same manner as the HC frames 34, with the exception that its right and left portions are formed integrally with each other (see FIG. 9). The WC frame 35 is provided with a guide groove 41 that enables the WC frame 35 to move vertically along a guide member 40 disposed in a base section 31 a of the rack 31. The guide members 40 are provided on both sides of the rack 31 so as to continuously extend in the vertical direction of the canister 21. Accordingly, it is configured such that the guide grooves 41 are guided by the guide members 40 provided in the canister 21 so that the WC frame 35 moves upward and downward.
Furthermore, by employing such a configuration that the WC frames 35 are allowed to move upward and downward along the guide members 40 provided on both sides of the rack 31, the WC frames 35, with the WC 38 disengaged from the tooth sections 32 of the rack 31, can be moved upward and downward along the canister 21. Therefore, even if the cross-section of the canister 21 increases as the pivoting-type thruster 22 increases in size, there is no need to increase the size of the WC frames 35, thereby making it possible for the elevation devices 30 to easily address the increase in the size of the vertically movable thruster apparatus 20.
Referring now to FIGS. 12 through 15, a description will be given of the vertical movement of the vertically movable thruster apparatus 20 by the above stated elevation device 30. This description will be given of fitting engagement and disengagement of the catch 36 by the HC cylinder 37 and fitting engagement and disengagement of the catch 38 by the WC cylinder 39. Also, a description will be given of a vertical movement of the rack 31 disposed in the canister 21 of the vertically movable thruster apparatus 20 by the elevation cylinder 33. Further, in the figures, the following are shown, i.e., the state of a limit switch operable to check the fitting engagement and disengagement of the catches 36, 38, the switching (changeover) between lower and upper positions of the limit switch, the valve operation state of the elevation cylinder 33 for moving upward and downward the catches 36, 38 and other like state. It is to be noted that the catch that supports the load of the vertically movable thruster apparatus 20 is shown hatched with a diagonal pattern. Further, a horizontal line is drawn in a part of the rack 31 so as to provide a clear understanding of the vertical movement of the rack 31.
Referring to (a) through (i) of FIG. 12 and (a) through (i) of FIG. 13, there is shown a vertical movement, with a positive downward load being applied to the catches 36, 38 from the rack 31 (i.e., in a state of: (thruster apparatus's own weight - buoyant force acting against thruster apparatus) > 0). FIG. 12 comprised of (a) to (i), depicts one cycle of the upward movement, and with reference to this figure, one cycle that moves the vertically movable thruster apparatus 20 upward will be described below.

(Upward Movement)
Referring to (a) of FIG. 12, there is depicted a state in which the vertically movable thruster apparatus 20 is supported by the HC 36 brought into fitting engagement with the tooth section 32 of the rack 31 by the HC cylinder 37 of the elevation device 30, and the description will start from this state.
Initially, the WC 38 is slightly moved upward (raised) by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the WC 38. This is followed by disengagement of the HC 36 from the tooth section 32 of the rack 31 (see (b) and (c) of FIG. 12).
Subsequently, the WC 38 is moved upward by the elevation cylinder 33, and while the HC 36 is pushed toward the rack 31 by the HC cylinder 37, the WC frame 35 is moved upward for one pitch distance of the rack 31. As a result of this, the HC 36 is brought into fitting engagement with the tooth section 32 located at one pitch lower position in the rack 31 (see (d) and (e) of FIG. 12).
Then, the WC 38 is slightly moved downward by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the lower HC 36. This is followed by disengagement of the WC 38 from the tooth section 32 of the rack 31 (see (f) and (g) of FIG. 12).
Next, the WC 38 is moved downward by the elevation cylinder 33, and while the WC 38 is pushed toward the rack 31 by the WC cylinder 39, the WC 38 is moved downward for one pitch distance of the rack 31. As a result of this, the WC 38 is brought into fitting engagement with the tooth section 32 located at one pitch lower position in the rack 31 (see (h) and (i) of FIG. 12).
The vertically movable thruster apparatus 20 thus moved upward for one pitch distance of the rack 31 is sequentially moved upward by repetition of the foregoing operation.

(Downward Movement)
FIG. 13 comprised of (a) to (i), depicts one cycle of the downward movement, and with reference to this figure, one cycle that lowers the vertically movable thruster apparatus 20 will be described below.
Referring to (a) of FIG. 13, there is depicted a state in which the vertically movable thruster apparatus 20 is supported by the HC 36 brought into fitting engagement with the tooth section 32 of the rack 31 by the HC cylinder 37 of the elevation device 30, and the description will start from this state.
Initially, the WC 38 is slightly moved upward by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the WC 38. This is followed by disengagement of the HC 36 from the tooth section 32 of the rack 31 (see (b) and (c) of FIG. 13).
Subsequently, the WC 38 is moved downward by the elevation cylinder 33, and while the HC 36 is pushed toward the rack 31 by the HC cylinder 37, the WC frame 35 is moved downward for one pitch distance of the rack 31. As a result of this, the HC 36 is brought into fitting engagement with the tooth section 32 located at one pitch upper position in the rack 31 (see (d) and (e) of FIG. 13).
Subsequently, the elevation cylinder 33 is slightly moved downward so that the load of the vertically movable thruster apparatus 20 is supported by the HC 36. This is followed by disengagement of the WC 38 from the tooth section 32 of the rack 31 (see (f) and (g) of FIG. 13).
Next, the WC 38 is moved upward by the elevation cylinder 33, and while the WC 38 is pushed toward the rack 31 by the WC cylinder 39, the WC frame 35 is moved upward for one pitch distance of the rack 31. As a result of this, the WC 38 is brought into fitting engagement with the tooth section 32 located at one pitch upper position in the rack 31 (see (h) and (i) of FIG. 13).
The vertically movable thruster apparatus 20 thus moved downward for one pitch distance of the rack 31 is sequentially moved downward by repetition of the foregoing operation.
Referring to (a) through (i) of FIG. 14 and (a) through (i) of FIG. 15, there is shown a vertical movement, with a negative upward load being applied to the catches 36, 38 from the rack 31 (i.e., in a state of: (thruster apparatus's own weight - buoyant force acting against thruster apparatus) < 0). FIG. 14, comprised of (a) to (i), depicts one cycle of the upward movement, and with reference to this figure, one cycle that moves the vertically movable thruster apparatus 20 upward will be described below.

(Upward Movement)
Referring to (a) of FIG. 14, there is depicted a state in which the vertically movable thruster apparatus 20 is supported by the HC 36 brought into fitting engagement with the tooth section 32 of the rack 31 by the HC cylinder 37 of the elevation device 30, and the description will start from this state.
Initially, the WC 38 is slightly moved downward by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the WC 38. This is followed by disengagement of the HC 36 from the tooth section 32 of the rack 31 (see (b) and (c) of FIG. 14).
Subsequently, the WC 38 is moved upward by the elevation cylinder 33, and while the HC 36 is pushed toward the rack 31 by the HC cylinder 37, the WC frame 35 is moved upward for one pitch distance of the rack 31. As a result of this, the HC 36 is brought into fitting engagement with the tooth section 32 located at one pitch lower position in the rack 31 (see (d) and (e) of FIG. 14).
Then, the WC 38 is slightly moved upward by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the lower HC 36. This is followed by disengagement of the WC 38 from the tooth section 32 of the rack 31 (see (f) and (g) in FIG. 14).
Next, the WC 38 is moved downward by the elevation cylinder 33, and while the WC 38 is pushed toward the rack 31 by the WC cylinder 39, the WC 38 is moved downward for one pitch distance of the rack 31. As a result of this, the WC 38 is brought into fitting engagement with the tooth section 32 located at one pitch lower position in the rack 31 (see (h) and (i) of FIG. 14).
The vertically movable thruster apparatus 20 thus moved upward for one pitch distance of the rack 31 is sequentially moved upward by repetition of the foregoing operation.

(Downward Movement)
FIG. 15, comprised of (a) to (i), depicts one cycle of the downward movement, and with reference to this figure, one cycle that lowers the vertically movable thruster apparatus 20 will be described below.
Referring to (a) of FIG. 15, there is depicted a state in which the vertically movable thruster apparatus 20 is supported by the HC 36 brought into fitting engagement with the tooth section 32 of the rack 31 by the HC cylinder 37 of the elevation device 30, and the description will start from this state.
Initially, the WC 38 is slightly moved downward by the elevation cylinder 33, whereby the load of the vertically movable thruster apparatus 20 is supported by the WC 38. This is followed by disengagement of the HC 36 from the tooth section 32 of the rack 31 (see (b) and (c) of FIG. 15).
Subsequently, the WC 38 is moved downward by the elevation cylinder 33, and while the HC 36 is pushed toward the rack 31 by the HC cylinder 37, the WC frame 35 is moved downward for one pitch distance of the rack 31. As a result of this, the HC 36 is brought into fitting engagement with the tooth section 32 located at one pitch upper position in the rack 31 (see (d) and (e) of FIG. 15).
Next, the WC 38 is slightly moved upward by the elevation cylinder 33 so that the load of the vertically movable thruster apparatus 20 is supported by the HC 36. This is followed by disengagement of the WC 38 from the tooth section 32 of the rack 31 (see (f) and (g) of FIG. 15).
Subsequently, the WC 38 is moved upward by the elevation cylinder 33, and while the WC 38 is pushed toward the rack 31 by the WC cylinder 39, the WC frame 35 is moved upward for one pitch distance of the rack 31. As a result of this, the WC 38 is brought into fitting engagement with the tooth section 32 located at one pitch upper position in the rack 31 (see (h) and (i) of FIG. 15).
The vertically movable thruster apparatus 20 thus moved downward for one pitch distance of the rack 31 is sequentially moved downward by repetition of the foregoing operation.
As has been described above, vertical (up-down) movement of the vertically movable thruster apparatus 20 by the elevation device 30 is accomplished employing a vertical movement technique that makes use of a so-called inchworm motion of short pitch.
Next, with reference to FIG. 16A, 16B to FIG. 21A, 21B, the operation of the vertically movable thruster apparatus which is vertically moved upward and downward by the above elevation device will be described. In FIG. 16A, 16B to FIG. 17A, 17B, the operation of the vertically movable thruster apparatus 20 according to a first embodiment (FIGS. 1, 2) is illustrated. In FIG. 18A, 18B to FIG. 21A, 21B, the operation of a vertically movable thruster apparatus 50 according to a second embodiment is illustrated. Hereinafter, the operation in the first embodiment and the operation in the second embodiment will be described.

(Operation of First Embodiment)
The vertically movable thruster apparatus 20 according to the first embodiment, shown in FIG. 16A, is an example in which the racks 31 disposed on the side portions of the canister 21 project upward from the upper end of the canister 21. In the first embodiment, the elevation devices 30 are fixed in a given position of the vertical passageway 2. The installation position of the elevation devices 30 is set such that the canister 21 can be moved upward to a position that allows for removal of the thruster 22 above the waterline W, as will be described later.
In the first embodiment, as shown in FIG. 16A, the thruster 22, having a height indicated by letter L in the figure and located in a position at which the thruster 22 projects downward from the ship's bottom 10 (i.e., in operative position), is moved upward by performing operation that causes the WCs 38 and the HCs 36 to alternately make fitting engagement and disengagement, as shown in (a) to (i) of FIG. 12 and (a) to (i) of FIG. 14. FIG. 16B shows a state in which the thruster 22 is in the stored position from the ship's bottom 10 (i.e., in navigating position).
Thereafter, by repetition of the operations shown in (a) to (i) of FIG. 12 or (a) to (i) of FIG. 14, the thruster 22 is moved upward to a position of the maintenance and inspection floor 11 situated in a predetermined position above the waterline W in the vertical passageway 2 (i.e., maintenance and inspection position), as shown in FIG. 17A. Then, as shown in FIG. 17B, the thruster 22 is detached from the canister 21 by workers at the maintenance and inspection floor 11 and then carried toward the maintenance and inspection floor 11. In this example, as shown in FIG. 17A, the height from the ship's bottom 10 to the waterline W is indicated by letter A, and the maintenance and inspection floor 11 lies in a position higher than the waterline W by a height indicated by letter B. A height space of the maintenance and inspection floor 11 is set so as to have a height of a working height C plus the height L of the thruster 22. Therefore, the amount of upward movement of the canister 21 is a height indicated by letter H.
In the way as has been described above, the configuration for raising the thruster 22 above the waterline W is implemented by the compact elevation device 30. This makes is possible to provide a vertically movable thruster apparatus 20, which can attain a situation in which even if the thruster 22 fails to operate properly in an offshore operation site, in situ inspection and repair can be carried out.

(Operation of Second Embodiment)
Next, with reference to FIG. 18A, 18B to FIG. 21A, 21B, the second embodiment will be described. The same components as those of the first embodiment are designated by the same reference numerals. In the second embodiment, in order that the HC frame 34 of each of the elevation devices 33 can also be moved upward and downward along the guide member 40 of the canister 21, its right and left portions are integral with each other and there is provided a guide groove 41, as in the WC frame 35 (see FIG. 11). The height of the racks 31 mounted in the canister 21 is set such that, in the position where the thruster 22 is stored inside the vertical passageway 2 (in the navigating position), the racks 31 do not project upward beyond the level of the deck (the level of the ship's hull 1 shown in the figure). Therefore, the second embodiment will be available even when no structure that projects upward during sailing or other like activity is acceptable. Further, the second embodiment is also available even when the level of the upper deck is too low to mount the elevation device 30 in a predetermined height position, as in the first embodiment.
According to the vertically movable thruster apparatus 50 of the second embodiment shown in FIG. 18A, the racks 31 are disposed on the side portions of the canister 21 such that they extends up to the upper end of the canister 21. In the second embodiment, the elevation devices 30 are firmly fixed in a predetermined position of the vertical passageway 2. However, the install position of the elevation devices 30 may be changed, as will be described later.
Also in the second embodiment, as shown in FIG. 18A, the thruster 22 in a projecting state from the ship's bottom 10 is moved upward by performing operation that causes the WCs 38 and the HCs 36 to alternately make fitting engagement and disengagement, by the elevation devices 30, as shown in (a) to (i) of FIG. 12 and (a) to (i) of FIG. 14. FIG. 18B shows a state in which the thruster 22 is in the stored position (i.e., in the navigating position), that is, the thruster 22 is stored inside from the ship's bottom 10. In the vertically movable thruster apparatus 50 of the second embodiment, in this state, there are no structures that project upward beyond the upper deck of the ship's hull 1.
Thereafter, by repetition of the operations shown in (a) to (i) of FIG. 12 or (a) to (i) of FIG. 14, the thruster 22 is moved upward close to the waterline W, as shown in FIG. 19A. With the thruster 22 being in such a state, the load of the vertically movable thruster apparatus 50 is temporarily held by load holding devices 12, i.e., devices adapted to support the load of the vertically movable thruster apparatus 50 by fitting engagement of a structure similar to the catches 36 with the tooth sections 32 of the rack 31 in a position indicated by two-dot chain line in the figure, which are disposed in the vertical passageway 2.
Then, the structure by which to firmly fasten the HC frames 34 of the elevation devices 30 to the ship's hull 1 are detached, thereby placing the elevation device 30 in a free state. By repetition of the operations illustrated in (a) to (i) of FIG. 15, the elevation devices 30 are moved upward to a predetermined upper position along the rack 31, as shown in FIG. 19B. This predetermined upper position is set such that the thruster 22 of the vertically movable thruster apparatus 50 can be moved upward to the position of the maintenance and inspection floor 11 provided above the waterline W, as will be described later.
Next, as shown in FIG 20A, there is provided, below the elevation devices 30 in the vertical passageway 2, load support structures 13. Then, as shown in FIG. 20B, each of the elevation devices 30 is moved downward for a given distance so that the HC frame 34 is firmly fastened to the load support structure 13. Thus, the load of the vertically movable thruster apparatus 50 is supported by the load support structures 13 via the elevation devices 30. Thereafter, the load holding devices 12 that are temporarily holding the load of the vertically movable thruster apparatus 50 are detached.
Then, by repetition of the operations shown in (a) to (i) of FIG. 12 or (a) to (i) of FIG. 14, the thruster 22 is moved upward to the position of the maintenance and inspection floor 11 provided in a predetermined position in the vertical passageway 2, as shown in FIG. 21A. Then, as shown in FIG. 21B, workers or other like service persons detach the thruster 22 from the canister 21 on the maintenance and inspection floor 11 and then move it to the maintenance and inspection floor 11.
In the way as has been described above, the configuration for raising the thruster 22 above the waterline W is implemented by the compact elevation devices 30. This makes is possible to provide a vertically movable thruster apparatus 20 which can attain a situation in which, even if the thruster 22 fails to operate properly in an offshore operation site, in situ inspection and repair can be carried out. Moreover, according to the vertically movable thruster apparatus 50 of the second embodiment, it is possible to eliminate structures that project upward for considerable distances.
As has been described above, according to the vertically movable thruster apparatus 20 (50), it is configured such that a pair of racks 31, 31 having a required length are disposed to extend vertically in the canister 21, and a pair of elevation devices 30 are disposed in a required height position in the vertical passageway 2. Thereby, the thruster 22 of the vertically movable thruster apparatus 20 (50) is stably movable upward and downward between the operative position and the maintenance and inspection position.
Besides, as a method for moving the vertically movable thruster apparatus 20 (50) upward and downward by means of the elevation devices 30, there is employed a method of repeating a so-called inchworm motion made by the elevation cylinders 33 of a short stroke, thereby making it possible to configure the elevation devices 30 in a compact and inexpensive manner. In addition, since it suffices that the stroke of the elevation cylinders 33 of the elevation devices 30 is short, this easily makes it possible for the elevation cylinders 33 to have a buckling strength enough to move upward and downward the vertically movable thruster apparatus 20 (50) of a heavy weight.
Moreover, because of the configuration that the bottom portions of the elevation cylinders 33 (regardless of the orientation thereof) are firmly fastened to the vertical passageway 2, the own weight of the vertically movable thruster apparatus 20 (50) is supported on the bore side having a larger area, thereby allowing for optimal design of the elevation cylinders 33.
Thus, it is also possible to provide a vertically movable thruster apparatus 20 (50) equipped with compact elevation devices 30 applicable to, at reduced costs, a drill ship or other like vessel equipped with a plurality of thrusters 22.
Incidentally, in order to accomplish vertical movement of the vertically movable thruster apparatus 20 (50), the predetermined spacings S1 and S2 are defined between the thruster apparatus 20 (50) and the vertical passageway 2. This will give rise to substantial fluctuations in the waterline W due to the influence of ocean waves or the like in sea areas located away from the land. In such a case, there is the possibility that normal operations may be hindered due to fluctuations in the waterline W when moving the vertically movable thruster apparatus 20 (50) upward and downward as described above.
To cope with this, as shown in FIGS. 1, 2, 7, the vertically movable thruster apparatus 20 (50) is equipped, in the positional level of the lateral-load support guides 3, 4 in the operative position, with the enclosing plates 7 which reduce the spacings S1, S2 between the entire circumference of the canister 21 and the entire circumference of the vertical passageway 2 to the smaller spacing S3 (FIG. 7) so as to effect the throttle effect thereof, as described above. The enclosing plates 7 are arranged at the lowermost support guides 3 and at the support and vertical-movement guides 4 that are situated at the lower side as described above, whereby the water surface between the vertical passageway 2 and the canister 21 is prevented from fluctuating considerably in the vertical direction, due to ocean waves, etc.. This embodiment is preferable in that, by provision of the enclosing plates 7 in the lowermost portion of the canister 21 in the operative position and in the position level of the support and vertical-movement guides 4 thereabove, the movement of water is suppressed surely.
In addition, in order to provide load holding during operation of the vertically movable thruster apparatus 20 (50), the relationship between the racks 31 and the catches 36, 38 may be as follows in consideration of ocean waves or the like as described above (see FIGS. 22 and 23). The direction of a static vertical load acting against the vertically movable thruster apparatus 20 is determined by the relationship between the own weight of the vertically movable thruster apparatus 20 and the magnitude of buoyant force acting against the vertically movable thruster apparatus 20 in a state in which no dynamic load due to ocean waves is acting.
FIG. 22 illustrates a state which is static and in which state a positive downward load is acting against the vertically movable thruster apparatus 20. That is, FIG. 22 illustrates a load holding state in which: (thruster's own weight - buoyant force acing against thruster) > 0.
According to the rack versus catch relationship illustrated in FIG. 22, the WC 38 incorporated in the WC frames 35 is pulled toward the HC frames 34 by the elevation cylinder 33, whereby the WC 38 and the HC 36 incorporated in the HC frames 34 push the rack 31 in opposite directions. As a result of this, the vertical movement of the canister 21 due to ocean waves during operation is suppressed.
In addition, FIG. 23 illustrates a state which is static and in which state a negative upward load is acting against the vertically movable thruster apparatus. That is, FIG. 23 illustrates a load holding state in which: (thruster's own weight - buoyant force acing against thruster) < 0.
According to the rack versus catch relationship illustrated in FIG. 23, the WC 38 incorporated in the WC frames 35 is pushed in the opposite direction relative to the HC frames 34 by the elevation cylinder 33, whereby the WC 38 and the HC 36 incorporated in the HC frames 34 pull the rack 31 in opposite directions. As a result of this, the vertical movement of the canister 21 due to ocean waves during operation is suppressed.
In addition, in a hydraulic circuit shown in FIGS. 22, 23, only diagrammatic representation of an accumulator 45, a low pressure relief valve 46a, a high pressure relief valve 46b, a check valve 47 and a tank 48, which are all provided to maintain the state that, by each of the elevation cylinders 33, the HC 36 and the WC 38 push or pull the rack 31 in the vertical direction, is provided, and diagrammatic representation of a pump, a direction switching valve and so on is omitted. The pressure in the accumulator 45 and the pressure in the low pressure relief valve 46a are set slightly higher than the pressure that allows each of the elevation cylinders 33 to move upward and downward the WC frame 35 in no load state.
As described above, it is configured such that the vertical static load acting against the canister 21 is held by the HCs 36 incorporated in the HC frames 34 which are firmly fastened to the vertical passageway 2. This holding is effected by placing the HCs 36 and the WCs 38 which are disposed at upper and lower positions in the elevation devices 30 in a push and pull state so that the dynamic load due to ocean waves acting in a direction opposite to the direction of the static load is held by the catches 36, 38. As a result of this, the vertical movement of the canister 21 due to ocean waves during operation is suppressed.
In the foregoing embodiments, a pair of racks 31 are disposed in the middle portion in the width direction, of opposing two outer surfaces of the canister 21 respectively such that the racks 31 vertically extend and face each other. However, for example, the racks 31 may be disposed diagonally as long as they pass through the horizontal cross-sectional center point of the canister 21. Further, two pairs of racks 31 may be provided, instead of one pair. That is, the racks 31 are not limited to those of the above embodiments.
Further, in the racks 31, the tooth sections 32 have a substantially rectangular shape. However, the tooth sections 32 may be formed into any shape as long as they have a convexoconcave shape of constant pitch so that, by fitting engagement with the catches 36, 38, the vertically movable thruster apparatus 20 (50) can be held. For example, the tooth sections 32 may be formed into a fitting engagement hole shape of constant pitch. That is, the shape of the tooth sections 32 is not limited to the shapes in the above embodiments.
Furthermore, the foregoing embodiments are described just by way of example only. Accordingly, various modifications can be made in the present invention within its scope. Thus, the present invention is not limited to the foregoing embodiments.

Industrial Applicability
The vertically movable thruster apparatus according to the present invention can be used in, for example, drill ships or the like that require that, at the time of occurrence of failure or the like, the thruster be moved upward to a position above the waterline for inspection and repair.

Reference Signs List
1:
ship's hull
2:
vertical passageway
3:
support guide
4:
support and vertical-movement guide
4a:
support guide section
4b:
vertical-movement guide section
5:
vertical-movement guide
6:
pad
7:
enclosing plate
8:
jack
9:
load support structure (fixing section)
10:
ship's bottom
11:
maintenance and inspection floor
12:
load holding device
13:
load support structure (fixing section)
20:
vertically movable thruster apparatus
21:
canister
22:
thruster
30:
elevation device
31:
rack
31a:
base section
32:
tooth section
33:
elevation cylinder
33a:
pin
34:
holding catch frame (HC frame)
34a:
guide section
35:
working catch frame (WC frame)
35a:
guide section
36:
holding catch (HC)
37:
holding catch drive cylinder (HC cylinder)
38:
working catch (WC)
39:
working catch drive cylinder (WC cylinder)
40:
guide section
41:
guide groove
50:
vertically movable thruster apparatus
S1, S2:
spacing
T:
clearance gap
W:
waterline
1. A vertically movable thruster apparatus, including a thruster disposed so as to project downward from a bottom thereof, and a canister which incorporates therein a drive device for driving the thruster and is vertically movable in a vertical passageway provided in a ship's hull,
the vertically movable thruster apparatus comprising:
at least one pair of racks of required length which are disposed in respective positions of outer surfaces of the canister that are opposite each other in a horizontal direction and each of which has tooth sections of constant pitch in a vertical direction;
guide members which are vertically disposed along the racks, respectively; and
one pair of elevation devices for bringing the canister into vertical movement between an operative position of the thruster and a position above a waterline along the one pair of racks in the vertical passageway, wherein
each of the one pair of elevation devices includes:
a pair of upper and lower catches which are independently brought into fitting engagement and disengagement with respective tooth sections in positions vertically spaced apart in the rack;
a pair of upper and lower frames equipped with the upper and lower catches, respectively; and
elevation cylinders each of which is disposed between the pair of upper and lower frames, and
each of the elevation cylinders is configured such that, with respect to one of the frames that is firmly fastened to the vertical passageway, the elevation cylinder moves the other frame vertically using the guide member as a guide.
2. The vertically movable thruster apparatus as set forth in claim 1, wherein the pair of upper and lower frames are mounted such that the lower frame is firmly fastened to the vertical passageway.
3. The vertically movable thruster apparatus as set forth in either claim 1 or claim 2, wherein
the vertical passageway includes a maintenance and inspection floor in a position above a waterline,
the canister includes racks of required length for upward movement of the thruster to the position of the maintenance and inspection floor, and
each of the elevation devices is disposed in a position of required height in the vertical passageway so that the thruster is movable upward from its operative position to the position of the maintenance and inspection floor.
4. The vertically movable thruster apparatus as set forth in any one of claims 1 to 3, wherein the pair of upper and lower frames include: drive cylinders for independently bringing the catches into fitting engagement and disengagement with the rack in an upper position and in a lower position, respectively; and guide sections for bringing the catches into fitting engagement and disengagement with respective tooth sections of the rack by extending and contracting motions of the drive cylinders.
5. The vertically movable thruster apparatus as set forth in any one of claims 1 to 4, wherein each of the elevation cylinders is configured such that, during operation of the thruster, the elevation cylinder brings the pair of upper and lower catches into fitting engagement with respective tooth sections of the rack to exert forces of opposite vertical directions on the catches thereby to hold a vertical load acting against the canister.
6. The vertically movable thruster apparatus as set forth in any one of claims 1 to 5, wherein
the vertical passageway includes:
fixing sections for the elevation device which are arranged in a plurality of positions vertically spaced apart; and
load holding devices for temporarily holding the load of the vertically movable thruster apparatus when effecting a change of the fixing sections, and
the elevation device includes fastening means detachable to the fixing sections of the vertical passageway.
7. The vertically movable thruster apparatus as set forth in any one of claims 1 to 6, wherein the vertical passageway includes: a support guide for supporting a horizontal force acting against the canister; and an enclosing plate which reduces in a position of the support guide, a spacing between the canister and the vertical passageway over an entire circumference.
8. The vertically movable thruster apparatus as set forth in claim 7, comprising a jack for supporting the canister in a horizontal direction, between the support guide and the canister.

REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description
- JP
4526184
B
[0008]
- JP
2001055197
A
[0008]