WO2013137729A1

WO2013137729A1 - Vessel comprising a crane

Info

Publication number: WO2013137729A1
Application number: PCT/NL2013/050168
Authority: WO
Inventors: Timothy Alexander Van Opstal
Original assignee: Ihc Holland Ie B.V.
Priority date: 2012-03-13
Filing date: 2013-03-13
Publication date: 2013-09-19
Also published as: NL2008473C2

Abstract

The invention relates to a vessel (1) comprising a crane (2). The crane (2) comprises a crane arm (20) which is rotatable about a crane axis of rotation (R) between an upper onboard position and a lower overboard position. The crane (2) comprises an elongated spring member (30) which is with one end (31) connected to the crane arm (20). The spring member (30) is put under tension when the crane arm (20) is in the upper onboard position, exerting a force to the crane arm (20) in the direction of the lower overboard position.

Description

Vessel comprising a crane

TECHNICAL FIELD

The invention relates to a crane and a vessel comprising such a crane and a method of operating such a crane.

STATE OF THE ART

Cranes or gantries on vessels are used to load or unload loads from or to the vessel. The cranes may also be used to hoist equipment from the vessel into the sea or from the sea onto the vessel. The vessel may be a dredging vessel, such as a trailing suction hopper dredger (TSHD) used for dredging operations. Such a vessel comprises suitable propulsion means. The equipment may for instance be dredging equipment, such as a suction pipe, a suction tube or excavation tool.

The crane may be formed by a crane arm, an actuator, such as a hydraulic cylinder, a (hydraulic) winch and a hoisting cable. The crane arm is rotatable connected to a deck of the vessel, such that actuator can rotate the crane arm about a substantial horizontal crane axis of rotation between an upper position and a lower position to move a load attached to the hoisting cable from an onboard position (upper position) to an overboard position (lower position) and vice versa. The hoisting cable can be controlled by a hydraulic winch to lower and lift the load attached to the hoisting cable. A pulley is provided at the top of the crane arm to guide the hoisting cable. An example of such a crane is provided by NL1004451C1.

So-called gravity cranes or gantries are known, in which the actuator for moving the crane arm is omitted. Instead, the rotatable movement of the crane arm is controlled by the winch. The crane arm can be lowered by giving out hoisting cable, causing the crane arm to be lowered under the influence of gravity, until the crane arm is prohibited from further downward movement as the lower position is reached, for instance by a stopping member. By giving out more hoisting cable, the load can be lowered with respect to the crane arm. By taking in hoisting cable, the load is lifted until it reaches a position against the top of the crane arm. Further taking in hoisting cable will move the crane arm from its lower position to its upper position. A locking mechanism may be provided to lock the crane arm in its upper position. Gravity cranes are cranes which are rotatable around a crane axis of rotation between an upper onboard position and a lower overboard position, where the crane, in an upper onboard position, is still on an outboard side of the crane axis of rotation. In other words, the crane is still outboard with respect to an upper dead point of the crane, i.e. a (theoretical) highest point. Cranes having an upper onboard position passed the upper dead point will always need a mechanism or the like for pushing the cranes passed this dead point in order to move the cranes to the lower overboard position.

Gravity cranes should be able to function in rough weather conditions, even when the vessel is tilted along a vessel axis (usually the longitudinal axis of the vessel running from bow to stern) parallel to the crane axis of rotation. If the vessel is tilted it may be difficult to lower the crane arm as the mass center point of the rotatable crane arm (possibly with a load attached to it) is no longer on an outboard side of the crane axis of rotation.

According to the prior art lowering could be ensured by positioning the crane axis of rotation relatively far away from the edge of the deck, which gives the crane a relatively large footprint. This is not an advantageous solution since deck area is always scarce, especially on vessels with small gangways or less space at the edge of the ship.

GB672554A describes davits used for supporting or launching ships boats or used in connection with accommodation ladders. The davit of a davit assembly is pressed outwardly by elastic means, such as a spring. GB778416 describes a similar device.

SHORT DESCRIPTION

It is an object of the invention to provide a gravity crane which has a relatively small foot print and can reliably be lowered also in rough weather conditions.

According to an aspect there is provided a vessel comprising a crane, the crane comprising a crane arm which is rotatable about a crane axis of rotation between an upper onboard position and a lower overboard position, wherein the crane comprises an elongated spring member which is with one end connected to the crane arm and the spring member is put under tension when the crane arm is in the upper onboard position, exerting a force to the crane arm in the direction of the lower overboard position. This ensures that the crane arm moves towards the lower overboard position when giving out the cable, even when the vessel is tilted, for instance caused by waves and wind. The crane can be positioned relatively close to the edge of the deck of the vessel, thereby reducing the foot print of the crane and providing a compact crane.

In the onboard position a top of the crane arm may be is above the deck of the vessel, while in the overboard position the top of the crane is in an overboard position. In the onboard position the top of the crane is horizontally closer to the vessel than in the overboard position.

The term tension is used to refer to a spring member not in its equilibrium state. For instance, in case the spring member is formed by an elongated spring element being a coil spring, a gas spring or a torsion spring, the spring member may be in a compressed or an extended state of the spring member.

The crane axis of rotation may be substantially horizontal and may be parallel to a deck edge of the vessel. In use, the vessel may move as a result of wind and waves. As will be understood, the term horizontal as used therefore refers to a direction substantially parallel to the deck of the vessel.

By using an elongated spring member which has spring characteristics in its elongated direction, the stroke of the spring can be relatively long. The spring member has an elongated shape and has a variable length in the elongated direction. Such spring members can take up a relatively large amount of energy within relatively small dimensions, making such spring members suitable for use in the field of dredging, where cranes are used for lifting and lowering heavy dredging equipment, such as suction pipes with drag heads attached to it.

This ensures that the crane is pushed towards the overboard position in a reliable way, even under severe conditions. Also, this ensures that the spring force is applied to the crane in an efficient way.

According to an embodiment the crane comprises a crane base attached to a deck of the vessel, wherein the crane arm is connected to the crane base by a rotatable connection allowing the crane arm to rotate about the crane axis of rotation, and the elongated spring member is with its other end rotatably connected to the crane base at a position remote from the crane axis of rotation.

The spring member is attached to the crane base at a position not coinciding with the crane axis of rotation to allow the spring member to exert a rotational force to the crane arm. The spring member is rotatable connected to the crane base and the crane arm to provide the spring member with the freedom of movement to follow the movements of the crane arm.

The spring member can be attached to the crane base or the vessel at a position behind and/or above the rotatable connecting of the crane arm. In such a case, the spring member may be a compression spring. Alternatively, the spring member can be attached to the crane base or the vessel at a position in front of the rotatable connecting of the crane arm. In such a case, the spring member may be an extension spring. The term in front as used here refers to a position in between the rotatable connection of the crane arm to the vessel and the edge of the deck. The term in behind as used here refers to a position behind the rotatable connection of the crane arm to the vessel with respect to the edge of the deck.

According to an embodiment the spring member is formed as an extending arm in which a spring element is provided. The extending arm may be a telescopic arm. Such spring members are able to take up large forces which makes them very suitable for use in the field of dredging, where cranes are used for lifting and lowering heavy dredging equipment, such as suction pipes with drag heads attached to it.

According to an embodiment the spring member is formed as a piston and a cylinder, wherein a spring element is provided inside the cylinder.

According to an embodiment the spring element is an elongated spring element, which has at least one loose end which is not attached to the spring member. In case the spring element is a compression spring, and is thus in a compressed state when the crane arm is in the upper onboard position, such a loose end has the advantage that when the spring element reaches its equilibrium length during downward movement of the crane arm, further downward movement is not hindered by the spring element which would otherwise reach an extended state and would exert an upward force to the crane arm.

The spring element could have two loose ends, especially in case the spring element is contained in the cylinder of a piston and cylinder assembly. However, the spring element may also have one loose end.

According to an embodiment two or more parallel elongated spring members are provided. For instance, in case the crane arm is formed as an A-frame, each leg of the crane arm may have an associated spring member. According to an embodiment the spring member comprises a spring element which is one of a coil spring, a gas spring, a torsion spring. A coil or helical spring is in particular able to function in an advantageous way, as the stroke of such a spring member can be relatively long. Such a coil or helical spring element can easily be implemented inside a spring member with one or two loose ends. Also a gas spring could be arranged with one or two loose ends.

Such spring members are able to take up large forces which makes them very suitable for use in the field of dredging, where cranes are used for lifting and lowering heavy dredging equipment, such as suction pipes with drag heads attached to it.

According to an embodiment the crane comprises stop means to stop the crane arm from moving beyond the lower overboard position.

In fact, the stop means define the lower overboard position. The stop means may be provided by a cable or chain which is with one connected to the crane arm and with its other end connected to the vessel or the crane base, which has a predetermined length which prevents the crane arm from rotating beyond the lower overboard position. The stop means may also be provided by a stop member attached to the vessel or the crane base against which the crane arm is lowered and which stops the crane arm from further downward movement. The stop means may be provided by an elongated member having a fixed length, such as a cable or chain, or by a stop block or the like.

According to an embodiment the crane is a gravity crane. The term gravity crane indicates that the crane arm can be lowered towards the lower outboard position under the influence of gravity, without the need of an actuator or the like to exert a force on the crane arm towards the lower outboard position. This implies that the crane, when in the upper onboard position the centre of gravity of the crane is on an outboard side of the crane axis of rotation.

According to the invention a spring member is added to the crane to ensure that the crane arm can also be lowered when the vessel is tilted backwards with respect to the overboard direction of the crane. It will be understood that the spring member is not needed for lowering a gravity crane when the orientation of the gravity crane is not tilted.

According to an embodiment the crane comprises a cable and cable control means to give out and take in the cable, wherein the crane arm can be lowered to the overboard position by giving out the cable and the crane arm can be lifted to the onboard position by taking in the cable.

According to an embodiment the cable is a hoisting cable arranged for lifting and lowering loads. The cable to lower and lift the crane arm can also be used to lower and lift loads. The crane arm may therefore comprise one or more pulleys arranged to guide the cable. The cable may be provided with a means to connect the cable to a load, such as a hook. The functioning of such a crane is as follows.

When the crane arm is in its upper onboard position, the crane arm may be locked by locking means to prevent the crane arm from moving towards the lower position. The spring member is under tension and pushes the crane arm towards the overboard position. Cable may be given out to lower the free end of the cable such that a load can be connected to the cable. Cable may be taken in, until no further cable can be taken in, as the load or the hook is pulled against the crane arm or a stop. Next, the locking means may be unlocked and cable may be given out to lower the crane arm until the crane arm reaches its lower outboard position, for instance because further downward motion is prevented by stop means. Giving out more cable will result in lowering of the free end of the cable and the load, for instance until the load reaches its destination, such as the see-floor.

Of course, the cable to lower and lift the crane arm and the hoisting cable may be separate cables, each having associated cable control means to give out or take in cable.

According to an embodiment the crane comprises locking means, to lock the crane arm in the upper onboard position. Such locking means can be formed by a hook or pin or by a cable or chain. Such a cable or chain may also function as stop means to prevent the crane arm from passing the lower overboard position.

According to an embodiment the vessel is a dredging vessel. In such a dredging vessel, the cable may permanently be connected to dredging equipment, such as a suction pipe, a suction tube or excavation tool. When not in use, the dredging equipment may be stored in a receptacle directly below the top of the crane arm when in the upper onboard position.

The crane may be suitable for use in the field of dredging, the crane therefore having a capacity of lifting and lowering loads of at least 15.000 kg (15 ton), preferably at least 50.000 kg (50 ton), possibly up to 200.000kg (200 ton). According to a further aspect there is provided a crane comprising a crane arm which is rotatable about a crane axis of rotation between an upper position and a lower position, wherein the crane comprises an elongated spring member which is with one end connected to the crane arm and the spring member is put under tension when the crane arm is in the upper onboard position, exerting a force to the crane arm in the direction of the lower overboard position. Such a crane can be a gravity crane.

According to a further aspect there is provided a method for operating a crane as described above on a vessel. The method may comprise applying locking means when the crane arm is in the upper onboard position to prevent the crane arm from moving towards the lower position.

SHORT DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figures 1, 2, 3 and 4 schematically depict a vessel with a crane according to an embodiment.

DETAILED DESCRIPTION

Embodiments will now be described by way of example with reference to the Figures.

The Fig.'s schematically depict a crane 2 mounted on a deck 5 of a vessel 1. The crane 2 comprises a crane arm 20 which can be rotated about a substantial horizontal crane axis of rotation R. The crane arm 20 may be formed as an A-frame, having two legs rotatably connected to the vessel and a crane top 3 where the two legs are joined. The crane 2 is a gravity crane.

The crane 2 can be moved between an upper onboard position (as shown in Fig. 1) and a lower overboard position (shown in Fig. 2). In the upper onboard position a crane top 3 is above the deck 5 of the vessel 1, while in the lower overboard position, the crane top 3 is in an overboard position and the crane arm 20 protrudes over the edge of the deck 5. By moving the crane 2 from the upper to the lower position (or vice versa), a load (not shown) can be moved from an onboard position to an overboard position (or vice versa).

A receptacle 6 may be mounted directly under the crane top 3 in the upper position. The receptacle 6 may be arranged to receive the load which is to be hoisted by the crane 1 from the receptacle 6 (onboard position) to an overboard position. The load may for instance be dredging equipment, such as a suction pipe or an excavation tool.

The crane arm 20 may be connected to the vessel 1 by means of a rotatable connection 25, which may be embodied in any suitable manner. The crane arm 20 may be rotatably connected to the deck 5 of the vessel 1. The crane 2 may also comprise a crane base 24 which is connected to the deck 5 of the vessel 1, the crane arm being rotatably connected to the crane base 24.

In the embodiment shown, the crane 2 comprises two parallel elongated spring members 30 (more clearly shown in Fig. 2). Of course, any suitable number of spring members 30 may be used, including one, three and four spring members 30. The spring members 30 have a variable length.

The spring members 30 are with one end 32 connected to the crane base 24, but may also be connected to the vessel 1 directly, such as the deck 5 of the vessel or a structure provided on the vessel 1. In general, the one end 32 of the spring member 30 may be attached to a fixed point on the vessel 1.

As shown in the figures, the one end 32 is connected above and behind the rotatable connection 25. The spring members 30 are therefore compression springs, as they are put under tension when the crane arm 20 is moved to its upper onboard position.

The other end 31 of the spring member 30 may be attached to the crane arm 20.

Both ends 31, 32 are connected using rotary connections 311, 322 to allow the spring member 30 to follow the rotary movement of the crane arm 20. Both rotary connections 311, 322 of the spring member 30 are not positioned on the crane axis of rotation R.

The spring member 30 is constructed such that it is put under tension when the crane arm 20 is in the upper onboard position such that a force is applied by the spring member 30 on the crane arm 20 towards the lower overboard position. When moving the crane arm 20 from the lower overboard position to the upper onboard position, the spring element is put under tension.

The spring member 30 has a variable length and may be formed as a telescopic arm comprising two or more telescopic elements in which a spring element, such as a coil spring or gas spring, is provided. The spring member 30 may also comprise a piston and a cylinder which are able to move with respect to each other, wherein inside the cylinder a spring element is provided, such as a coil spring or gas.

To prevent the spring element from hindering the downward movement when the spring element reaches its equilibrium length, the spring element may comprise one or two loose ends. For instance, in case the spring element is a coil spring or gas spring provided inside an extending spring member (e.g. inside a cylinder of a telescopic arm), one end of the spring element may be provided loosely such that it can travel with respect of the crane arm. As a result, when the crane arm continues to move in downward direction beyond the equilibrium length of the spring element, the loose end of the spring element can move inside the spring member such that no spring force is exerted on the crane arm during this further downward movement.

According to an alternative embodiment, the spring element may be fixedly connected to the spring member with two ends. Depending on the spring

characteristics, two situations may occur.

According to a first situation, the equilibrium length of the spring element 30 may be reached at an intermediate position of the crane arm 20. This has the advantage that the spring element 30 will exert an upward force to the crane arm 20 when the crane arm is lowered beyond this intermediate position, helping to lower the crane arm 20 in a gentle way and preventing the crane arm from crashing into its lower position. Also, when the crane arm 20 is in its lower overboard position and would move up and down due to wave motions of the vessel, the upward force of the spring element 30 would prevent the crane arm 20 from crashing into its lower overboard position and thereby damaging the vessel.

In the second situation, the equilibrium length of the spring element 30 is such that the spring element 30 provides a downward motion to the crane arm 20 over the whole path between the upper onboard position and the lower overboard position. This has the advantage that even when the crane arm 20 is in its lower overboard position, a downward force is exerted to the crane arm 20. This prevents the crane arm 20 from moving up unintentionally as a result of wave motions of the vessel.

The Figures further show an example of stop means 26 provided to limit the freedom of movement of the crane arm 20 in downward direction. The stop means in fact define the lower outboard position. In the example shown, the stop means 26 is provided by a cable 26 of fixed length which is with a crane end 261 connected to the crane arm 20, preferably near the crane top 3, and which is with a vessel end 262 connected to the crane base 24, preferably to an upwardly protruding frame part 27 connected to the crane base 24. The vessel end 262 of the cable 26 may alternatively be connected to a fixed point of the vessel. The length of the cable 26 is chosen carefully to define the lower overboard position of the crane arm 20.

The crane comprises a cable 21 and cable control means 22 to the cable 21. The control means 22 may be a winch, automatically or manually operated. The cable control means 22 may give out and take in cable 21 to move the crane arm 20 between the upper onboard and lower overboard position. The upwardly protruding frame part 27 may comprise an opening through which the cable 21may be guided.

The cable 21 may be a separate cable which is with one end connected to the crane arm 20, for instance close to the top 3 of the crane such that the cable control means 22 can lower and lift the crane arm 20 by giving out and taking in cable 21.

As shown in the Fig.'s, the cable 26 may also function as hoisting cable 21. Close to the top of the crane 3, a cable guiding element 28, such as a pulley is provided for guiding the hoisting cable 26. The cable may be provided with a means to connect the cable to a load, such as a hook 29.

Fig. 4 schematically shows a vessel comprising a plurality of cranes according to the embodiments, the cranes being in the lower overboard position with a load suspended under water.

Descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. Vessel (1) comprising a crane (2), the crane (2) comprising a crane arm (20) which is rotatable about a crane axis of rotation (R) between an upper onboard position and a lower overboard position, wherein the crane (2) comprises an elongated spring member (30) which is with one end (31) connected to the crane arm (20) and the spring member (30) is put under tension when the crane arm (20) is in the upper onboard position, exerting a force to the crane arm (20) in the direction of the lower overboard position.

2. Vessel according to claim 1, wherein the crane (2) comprises a crane base (24) attached to a deck of the vessel (1), wherein the crane arm (20) is connected to the crane base (24) by a rotatable connection (25) allowing the crane arm (20) to rotate about the crane axis of rotation (R), and the elongated spring member (30) is with its other end rotatably connected to the crane base (24) at a position remote from the crane axis of rotation (R).

3. Vessel according to any one of the preceding claims, wherein the spring member (30) is formed as an extending arm in which a spring element is provided.

4. Vessel according to any one of the preceding claims, wherein the spring member (30) is formed as a piston and a cylinder, wherein a spring element is provided inside the cylinder.

5. Vessel according to any one of the claims 3 - 4, wherein the spring element is an elongated spring element, which has at least one loose end which is not attached to the spring member.

6. Vessel according to any one of the preceding claims, wherein two or more parallel elongated spring members (30) are provided.

7. Vessel according to any one of the preceding claims, wherein the spring member (30) comprises a spring element which is one of a coil spring, a gas spring, a torsion spring.

8. Vessel according to any one of the preceding claims, wherein the crane (2) comprises stop means (26) to stop the crane arm (20) from moving beyond the lower overboard position.

9. Vessel according to any one of the preceding claims, wherein the crane is a gravity crane.

10. Vessel according to any one of the preceding claims, wherein the crane (2) comprising a cable (21) and cable control means (22) to give out and take in the cable (21), wherein the crane arm (20) can be lowered to the overboard position by giving out the cable (21) and the crane arm (20) can be lifted to the onboard position by taking in the cable (21).

11. Vessel according to claim 10, wherein the cable (21) is a hoisting cable (21) arranged for lifting and lowering loads.

12. Vessel according to any one of the preceding claims, wherein the crane comprises locking means, to lock the crane arm (20) in the upper onboard position.

13. Vessel according to any one of the preceding claims, wherein the vessel or crane comprises locking means to lock the crane arm in its upper onboard position.

14. Vessel according to any one of the preceding claims, wherein the vessel is a dredging vessel.

15. Crane comprising a crane arm (20) which is rotatable about a crane axis of rotation (R) between an upper position and a lower position, wherein the crane (2) comprises an elongated spring member (30) which is with one end (31) connected to the crane arm (20) and the spring member (30) is put under tension when the crane arm (20) is in the upper onboard position, exerting a force to the crane arm (20) direction of the lower overboard position.

16. Method for operating a crane on a vessel according to any one of the claims 1 - 14.