WO2001089919A1

WO2001089919A1 - A locking mechanism, especially for the locking of a buoy

Info

Publication number: WO2001089919A1
Application number: PCT/NO2001/000218
Authority: WO
Inventors: Per Heen; Kjetil Hagland
Original assignee: Navion Asa
Priority date: 2000-05-26
Filing date: 2001-05-25
Publication date: 2001-11-29
Also published as: NO20002705D0; NO20002705L; AU2001262809A1; NO312354B1

Abstract

A mechanism for releasable locking of an element in relation to a base, especially for the locking of a buoy (2) in a downwardly open receiving space (3) in a floating vessel. The mechanism comprises a rotatably mounted locking arm (6) which is pivotable between a release position and a locking position in which an abutment edge (7) on the locking arm (6) is in engagement with an abutment edge (8) on the element (2) to be locked, a linkage (9) which is connected between the locking arm and the base (5) and which, in the locking position, is in a self-locking over-centre position, and a driving means (17-20) for actuation of the linkage (9). The linkage (9) comprises a length-adjustable first link (10) which, from an initial position with the locking arm (6) close to its locking position, is arranged to be extended to thereby pivot the locking arm additionally to a final locking position, for achieving a desired preloading force in the engagement between the abutment edges (7 and 8) of the locking arm (6) and the element (2). The first link (10) preferably is a hydraulic cylinder cylinder having a piston rod (12) of which one end is connected to the locking arm (6).

Description

A locking mechanism, especially for the locking of a buoy

The invention relates to a mechanism for releasable locking of an element in relation to a base, especially for the locking of a buoy in a downwardly open receiving space in a floating vessel, comprising a rotatably mounted locking arm which is pivotable between a release position and a locking position in which an abutment edge on the locking arm is in engagement with an abutment edge on the element to be locked, a linkage which is connected between the locking arm and the base and which, in the locking position, is in a self-locking over-centre position, and a driving means for actuation of the linkage.

A mechanism of the above-mentioned type for example is known from USSR inventor certificate No. 912 622. There are previously known different types of locking mechanisms for releasable locking of buoys to vessels in connection with offshore production of hydrocarbons. A special system in this field is the so-called STL or STP system, wherein STL stands for "Submerged Turret Loading" and STP stands for "Submerged Turret Production". In this system there is used a conically shaped, two-part buoy which is pulled into a conically shaped receiving space at the bottom of a ship. An outer member of the buoy is locked in position by means of a hydrauhcally operated locking mechanism. Anchor lines are fixed to a central member of the buoy, so that the ship, when the buoy is locked in the receiving space, will be anchored and may turn about the central member of the buoy under the influence of the weather conditions. A locking mechanism for such a buoy for example is known from US patent specification No. 5 529 571. This mechanism comprises only two locking dogs having relatively small abutment surfaces which absorb all vertical forces. The mechanism is intended for buoys having a diameter of up to 2 700 mm, and is less suitable for larger buoys wherein larger anchoring forces occur. The development of the STL/STP system recently has gone in the direction of larger buoys and larger forces from the anchoring system. Therefore, there is a need for a ' locking mechanism which can absorb relatively large anchoring forces, at the same time as it can meet the requirements made with respect to safety in use.

On this background it is a principal object of the invention to provide a locking mechanism which is able to lock buoys of the relevant type with a desired preloading force in offshore fields where the anchoring forces are large, or in fields requiring larger buoys.

Further objects of the invention are to provide such a locking mechanism which may be independent of hydraulic pressure to keep the buoy mechanically locked with the desired preloading force when the mechanism is in the locked position, and which may also have a quick disconnect function.

For achieving the above-mentioned objects there is a provided a mechanism of the introductorily stated type which, according to the invention, is characterised in that the linkage comprises a length-adjustable first link which, from an initial position with the locking arm close to its locking position, is arranged to change its length to thereby pivot the locking arm additionally to a final locking position, for achieving a desired preloading force in the engagement between the abutment edges of the locking arm and the element. In an advantageous embodiment of the mechanism according to the invention the linkage is constituted by a first link and a second link in the form of an arm of which one end is rotatably connected to the first link, and of which the other end is rotatably mounted in a frame supported by the base, the first link being connected to the locking arm. Further, it is advantageous that the first link is a hydraulic cylinder having a piston rod of which one end is connected to the locking arm.

The invention will be further described below by means of exemplary embodiments with reference to the drawings, wherein

Fig. 1 shows a schematic side view of a first embodiment of the mechanism according to the invention, with the locking arm in its release position in relation to the upper part of a buoy shown in section;

Fig. 2 shows a view essentially corresponding to Fig. 1, with the locking arm in the locking position;

Fig. 3 shows a schematic plan view of the locking mechanism and the buoy according to Fig. 2;

Fig. 4 shows a schematic side view of a second embodiment of the mechanism according to the invention, with the locking arm in its release position in relation to the upper part of a buoy which is shown in section;

Fig. 5 shows a view corresponding to Fig. 4, with the locking arm in the locking position;

Fig. 6 shows a schematic plan view of the locking mechanism and the buoy according to Fig. 5; and

Figs. 7 and 8 show side views of the same embodiment of the locking mechanism as the one shown in Figs. 4 and 5, but wherein the assembly of the mechanism in the supporting frame is modified in relation to the assembly of Figs. 4 and 5.

Even if the invention in the following will be described in connection with the locking of a buoy, it will be appreciated that the locking mechanism can also be adapted for use in other fields, for example in connection with a chain stopper. In the embodiment of Figs. 1-3 there is shown a locking mechanism 1 for releasable locking of a buoy 2 in a receiving space in a vessel. The drawing shows only an upper part of the buoy, and the receiving space is symbolically designated by 3. The mechanism is assembled in a frame 4 which is supported by a foundation or base 5 on the vessel, for example the deck of the vessel. In the drawing there is shown only one locking mechanism 1 in connection with the buoy. It will be clear, however, that in practice there will be arranged several mechanisms, for example 3 or 4, which will be distributed with equal angular distances around the circumference of the bouy.

As shown, the mechanism comprises a locking arm or locking jack 6 which is rotatably mounted in the frame 4 in a rotating connection A, and which is pivotable between a release position and a locking position in which an abutment edge 7 on the locking arm 6 is in engagement with an abutment edge 8 on the buoy 2. In the pivot point A all vertical forces will be transferred to the base 5 via the frame 4.

The locking arm 6 at its free end is rotatably connected to a linkage 9 in a rotating connection B. The linkage consists of a first link 10 and a second link 11 which are rotatably connected to each other in a common rotating connection C. The second link is rotatably mounted in the frame 4 in a rotating connection D, and is coupled to a driving means which will be further described below. In the locking position of the locking arm (shown in Fig. 2) the linkage 9 is in a self-locking over-centre position as further described below.

In accordance with the invention, the first link 10 is designed as a length- adjustable link which, from an initial position with the locking arm 6 close to its locking position, is arranged to change the length to thereby pivot the locking arm additionally to a final locking position in which the abutment edge 7 of the locking arm is preloaded with a desired force against the abutment edge of the element to be locked, in the illustrated case the abutment edge 8 of the buoy 2.

As will be realised by a person skilled in the art, the desired length adjustment of the link 10 may be achieved by means of different arrangements, for example by means of a mechanically length-adjustable device. In the illustrated preferred embodiment the length-adjustable link 10 is a hydraulic cylinder having a piston rod 12 of which one end is connected to the locking arm 6 in the rotating connection B.

As appears from Fig. 3, the second link 11 in the illustrated embodiment consists of a double crank arm 13 which is pivotable from a first position ( Fig. 1) in which the locking arm 6 is in its release position, in the direction away from the locking arm to a second position (Fig. 2) in which the linkage 9 is in the over-centre position with the common rotating connection C of the linkage and its rotating connection B with the locking arm 6 situated on opposite sides of the bearing point D of the linkage in the frame 4. The over-centre position is achieved in that the crank arm 13 is pivoted past a lower dead centre of the linkage, which dead centre is defined in that the rotating connections B, C and D lie on a straight line.

In the over-centre position, the second link 11 rests against a supporting element 14 which prevents further pivoting movement of the linkage. As appears from Fig. 2, the piston rod 12 in the hydraulic cylinder 10 is through- going, and at the opposite end of the rod in relation to the connection with the locking arm 6 the rod is provided with a means for mechanical locking of the rod in relation to the cylinder 10, after the cylinder has been activated and has placed the locking arm in its final locking position. In the illustrated embodiment this locking means consists of a nut 15 which is threaded onto a threaded portion of the rod end, and a distance ring (not shown) bearing against the adjacent end of the hydraulic cylinder 10.

Next to the supporting element 14 a hydraulic cylinder 16 is fitted under the second link 11, or preferably a hydraulic cylinder under each of the crank arms 13, in order to return the second link from the over-centre position and past said dead centre, in connection with an emergency release of the locking mechanism. In this manner there is achieved a safe and quick emergency release, something which is essential in an emergency situation.

As mentioned above, the second link 11 is coupled to a driving means for achieving said movement of the linkage when the locking arm is to be brought to its locking position, or for opposite movement of the linkage in case of a planned release of the locking mechanism, for example in connection with maintenance. In the illustrated embodiment the driving means comprises a gear wheel 17 placed on a shaft 18 forming part of the rotatable mounting of the second link 11 in the frame 4, and a toothed rack 19 which is an engagement with the gear wheel 17 and is displaceable to the necessary extent by means of a hydraulic cylinder 20.

The illustrated driving means only represents an example. Instead of a toothed rack and a hydraulic cylinder there might be used, for example, a hydraulic motor and a gear wheel, or a hydraulic cylinder may be coupled directly to the locking arm.

An operation cycle in the locking of a buoy by means of the embodiment according to Figs. 1-3 will be further described below.

The buoy 2 is pulled into the receiving space 3 of the ship by means of a pulling winch and a hawser connected to the buoy. When the buoy is confirmed "in position" by a pair of sensors (not shown), the buoy is ready for locking. When the buoy is ready for locking, the double crank arm 13 is pivoted by means of the driving means and pulls with it the hydraulic cylinder 10 and the locking arm 6. The hydraulic cylinder is not operative at this time. The crank arm 13 is rotated until it comes past the lower dead centre and after a few degrees of further rotation comes into abutment against the supporting element 14. The locking mechanism is now in the over-centre position, and can not be released without the use of hydraulic force by means of the cylinder (or cylinders) 16, or by the use of the driving means in case of a normal or planned release of the locking mechanism.

When the crank arm 13 has landed on the supporting element 14, there will typically be clearance of 10-20 mm between the abutment edges 7 and 8 of the locking arm and the buoy. At this point of time the hydraulic cylinder 10 is activated, and the piston rod 12 is moved so that the locking arm 6 is pivoted additionally and said abutment edges are brought in contact with each other. When contact is achieved, the hydraulic pressure is further increased in order to pull the buoy additionally into the receiving space, and so that the desired preload is achieved in the engagement between the abutment edges of the buoy and the locking arm. The correct pressure is maintained in the cylinder 10 until a manual tightening of the nut 15 on the piston rod can be undertaken, so that it comes into abutment against the distance ring. When this has been done, the pressure in the cylinder may be released, and the buoy then is mechanically locked with the correct preload. In case of a possible emergency disconnection, the hydraulic cylinder or cylinders 16 is/are used to push the crank arm 13 somewhat upwards past the dead centre. As the crank arm passes the dead centre, the locking arm will be rotated because of the weight from the buoy. The rotating means 17-20 will provide for a damped movement of the locking mechanism in an emergency disconnection. Under normal circumstances the steps in a disconnection of the mechanism will be carried out in the opposite order of the operation cycle described above.

A second embodiment of the locking mechanism according to the invention is shown in Figs. 4-6. These figures show a locking mechanism which to a substantial extent corresponds to the locking mechanism according to Figs. 1-3, but wherein especially the linkage is designed in a somewhat different manner. For avoidance of unnecessary reiteration, reference is therefore also made to the preceding description as regards the construction and operation of the mechanism.

In a corresponding manner to that of Figs. 1-3, Figs. 4-6 show a mechanism which is intended for locking of a buoy 2 in a receiving space 3 in a vessel. The mechanism, which is here designated by 30, is assembled in a frame 4 which is supported by a base 5, for example a deck on the vessel in question. The mechanism has a locking arm or locking jack 31 having essentially the same design as the locking arm/locking jack 6 in the first embodiment. The abutment edge of the locking arm for engagement with the abutment edge 8 of the buoy 2 here is designated by 32. The mechanism comprises a linkage 33 consisting of a first link 34 and a second link 35 which are connected to the locking arm 31 and the frame 4, respectively, in a corresponding manner to that of the first embodiment. The length-adjustable link 34 also in this embodiment consists of a hydraulic cylinder having a piston rod 36 which at one end is connected to the locking arm 31 in the rotating connection B. This end of the rod 36 is provided with a threaded portion having a nut 37 which may be tightened to abutment against a distance ring 38, in a similar manner as in the first embodiment, for mechanical locking of the rod in relation to the cylinder, after that the cylinder has been activated and has moved the locking arm 31 to the final locking position thereof. The second link 35 consists of a link arm which, under the influence of the driving means of the mechanism, is rotatable from a first position (Fig. 4) in which the link arm 31 is in its release position, in the direction towards the locking arm to a second position (Fig. 5) in which the linkage 33 is in the over-centre position with the common rotating connection C of the linkage situated between the rotating connection B with the locking arm and the bearing point D of the linkage in the frame. The link arm 35 then is pivoted past the dead centre of the linkage which is defined by the rotating connections B, C and D being situated on a straight line.

In the over-centre position the link arm 35 rests against a supporting element 39 which prevents further movement of the linkage. The driving means of the mechanism, for movement of the linkage when the locking arm 31 is to be brought to its locking position, in this embodiment is shown to consists of a hydraulic cylinder 40 which is connected between the link arm 35 and the base 5. As an alternative to the shown driving means, there might be used, for example, a hydraulic motor and a gear wheel, or a toothed rack and a gear wheel, as in the first embodiment.

Also in this embodiment, next to the supporting element 39, there is fitted a hydraulic cylinder 41, or possibly a pair of cylinders, under the link arm 35, in order to return the linkage past the dead centre in connection with an emergency release of the locking mechanism, as in the first embodiment. The manner of operation of the locking mechanism according to Figs. 4-6 corresponds to the manner of operation of the first embodiment. Therefore, reference is made to the operation cycle of the first embodiment described above.

As appears from Fig. 5, the lower part of the locking arm 31 is situated in a recess 41 in the base 5, i.e. the deck of the vessel, when the linkage 33 is in the over- centre position and the locking arm 31 is in its locked position. This enables a low building height of the locking mechanism. If one wants to avoid such a recess in the deck, and where a low building height is not a requirement, a corresponding locking mechanism may be fitted in a somewhat higher frame 4, more specifically by raising the place of mounting of the link arm in the frame to a higher level. Such a modified assembly is shown in Figs. 7 and 8.

By means of the locking mechanism according to the invention there may be obtained a number of advantages which may be summarised as follows: Increased accessibility. When several locking mechanisms are distributed about a buoy, one may repair or maintain one mechanism at a time without this affecting the locking capacity of the system. It will also be possible to replace a complete locking mechanism without this having an influence on the locking of the buoy.

Better distribution of forces between buoy and locking mechanism.

• The locking mechanism will be easy to install. The mechanism will be able to be produced and assembled as a unit together with the relevant frame. The installation may take place by screw mounting or by welding against the base.

• Surrounding steel structures will only see the forces from the buoy. All other forces in connection with the locking arrangement will be equalised or absorbed internally in the locking mechanism.

The mechanism will endure standing under water for longer time periods.

• It is simple to check the preloading of the buoy by supplying the correct pressure to the hydraulic cylinder.

The locking mechanism will be "dead" during operation, and is not dependent on a maintained hydraulic pressure.

• The mechanism is flexible with respect to forces from the buoy, and is adapted for different buoy sizes. The number of locking jacks may be varied dependent on the requirement.

Claims

Patent claims

1. A mechanism for releasable locking of an element in relation to a base, especially for the locking of a buoy (2) in a downwardly open receiving space (3) in a floating vessel, comprising a rotatably mounted locking arm (6; 31) which is pivotable between a release position and a locking position in which an abutment edge (7; 37) on the locking arm (6; 31) is in engagement with an abutment edge (8) on the element (2) to be locked, a linkage (9; 33) which is connected between the locking arm and the base (5) and which, in the locking position, is in a self-locking over-centre position, and a driving means (17-20; 40) for actuation of the linkage (9; 33), characterised in that the linkage (9; 33) comprises a length-adjustable first link (10; 34) which, from an initial position with the locking arm (6; 31) close to its locking position, is arranged to change its length to thereby pivot the locking arm additionally to a final locking position, for achieving a desired preloading force in the engagement between the abutment edges (7; 32 and 8) of the locking arm (6; 31) and the element (2).

2. A mechanism according to claim 1, characterised in that the linkage (9; 33) is constituted by a first link (10; 34) and a second link (11; 35) in the form of an arm of which one end is rotatably connected with the first link (10; 34), and of which the other end is rotatably mounted in a frame (4) supported by the base (5), the first link (10; 34) being connected to the locking arm (6; 31).

3. A mechanism according to claim 2, characterised in that the first link (10; 34) is a hydraulic cylinder having a piston rod (12; 36) of which one end is connected to the locking arm (6; 31).

4. A mechanism according to claim 2 or 3, characterised in that the second link

(11) is constituted by a crank arm (13) which, under the influence of the driving means (17-20), is pivotable from a first position in which the locking arm (6) is in its release position, in the direction away from the locking arm to a second position in which the linkage (9) is in the over-centre position with the common rotating connection (C) of the linkage and its rotating connection (B) with the locking arm (6) situated on opposite sides of the rotatable mounting (D) of the linkage (9) in the frame (4), with the crank arm (13) resting against a supporting element (14) and with the locking arm (6) situated close to its final locking position.

5. A mechanism according to claim 3 and 4, characterised in that the piston rod

(12) of the cylinder (10) is through-going, and that the rod (12), at the opposite end in relation to the connection with the locking arm (6), is provided with a means (15) for mechanical locking of the rod (12) in relation to the cylinder (10), after activation of the cylinder for placing of the locking arm (6) in its final locking position.

6. A mechanism according to claim 5, characterised in that the means for mechanical locking comprises a nut (15) which is threaded onto a threaded portion of the end of the piston rod (12), and a distance ring placed between the nut (15) and the end in question of the cylinder (10).

5 7. A mechanism according to one of the claims 4-6, characterised in that the driving means comprises a gear wheel (17) placed on a shaft (18) forming part of the rotatable mounting of the second link (11) of the linkage (9) in the frame (4), and a toothed rack (19) which is in engagement with the gear wheel (17) and its displaceable by means of a hydraulic cylinder (20). o 8. A mechanism according to claim 2 or 3, characterised in that the second link

(35) is constituted by a link arm which, under the influence of the driving means (40), is pivotable from a first position in which the locking arm (31) is in its release position, in the direction towards the locking arm (31) to a second position in which the linkage (33) is in the over-centre position with the common rotating connection (C) of the linkages situated between the rotating connection (B) with the locking arm (31) and the rotatable mounting (D) of the linkage (33) in the frame (4), with the link arm (35) resting against a supporting element (39) and with the locking arm (31) situated close to its final locking position.

9. A mechanism according to claim 8, characterised in that the piston rod (36)0 of the cylinder (34) at the end which is connected to the locking arm (31) is provided with a threaded portion having a nut (37) that can be screwed to abutment against a distance piece (38), for mechanical locking of the rod (36) in relation to the cylinder (34), after activation of the cylinder for placing of the locking arm (31) in its final locking position. 5

10. A mechanism according to claim 8 or 9, characterised in that the driving means (40) comprises a hydraulic cylinder which is connected between the link arm (35) and the base (5).

11. A mechanism according to one of the claims 4-10, characterised in that it comprises a hydraulic cylinder (16; 41) which is arranged to return the second link (11;o 35) from the over-centre position and past the dead centre in question of the linkage (9; 31) in connection with an emergency release of the locking mechanism (1; 30).