EP2411266B1

EP2411266B1 - A hydraulic mooring cable holding device

Info

Publication number: EP2411266B1
Application number: EP10711090.0A
Authority: EP
Inventors: Willem Cornelis Zegelaar
Original assignee: ShoreTension Holding BV
Current assignee: ShoreTension Holding BV
Priority date: 2009-03-27
Filing date: 2010-03-29
Publication date: 2013-06-05
Anticipated expiration: 2030-03-29
Also published as: WO2010110666A3; ES2426760T3; PT2411266E; EP2411266A2; WO2010110666A2; AU2010229451A1; CY1114551T1; NL2002680C2; AU2010229451B2; DK2411266T3; PL2411266T3; NZ595794A

Description

Field of the invention

The invention relates to a mooring cable holding device for keeping a ship moored, a mooring system for mooring ships using such a device and to a method of mooring ships.

Background

As is well known, heavy see-going ships are usually moored to the shore using cables (hawsers) that are fastened on the ship and on shore. An important factor in mooring is the force on the cable: if this force becomes excessive, the cable will break. Winches onboard ship may be used to control the force on the cables. Such winches can be kept permanently active to prevent that the forces on the cable rise above breaking strength during wind gusts. US 3886 887 constitutes the closest prior art.
However, under extreme wind conditions the protection against breaking can become unreliable. Even when winches are used, the winches can lock during severe gales or run loose, ultimately resulting in a broken cables and a ship that goes partly adrift in port, with the risk of considerable damage. Also when power on the winches fails during a gale, broken cables may be the result. Accordingly, a need exists for more reliable systems. The prior art has looked for better winch design, or use of shore based vacuum suction cups or magnets to keep ships attached to the shore as a replacement of cables. However, such solutions are very energy consuming and susceptible to failure.
US 6,439,147 describes an offshore mooring system with an arm to exert a torque on the ship to force it towards a quiescent position. US 6,439,147 describes the use of hydraulic mooring devices that are actively controlled or used as hydraulic dampers. The hydraulic mooring devices are part of a rigid structure that couples a mooring turret to the ship. When used a damper, hydraulic fluid from a first side of a piston is passed to a second side through a damping orifice. A relief valve allows the fluid to flow to a reservoir from the first side if the movement becomes to fast and from the reservoir to the second side through a check valve. Thus, damping is provided as well as protection against excessive forces.
JP62-2012584 describes a mooring device with a hydraulic mooring device that contains a piston attached to a mooring cable. This device comprises a control system that is configured to keep the cable under tension. When the tension on the cable is small, a pump is used to supply additional hydraulic fluid to the hydraulic mooring device, in order to pull in the rope. On the other hand, when the tension on the cable is high, hydraulic fluid is released from the hydraulic mooring device.
However, this device is subject to failure when the power supply of the pump fails. Nor does the device specifically address protection against excessive forces.

Summary

Among others, it is an object to provide for a device that makes it possible to use cables to keep a ship moored with robust protection against excessive forces on the cables.
A mooring cable holding device according to claim 1 is provided. This device may be coupled in series with a mooring cable of a ship. It has a hydraulic cylinder with a piston in the hydraulic cylinder and a reservoir for hydraulic liquid and gas. Operationally, the reservoir and a part of the hydraulic cylinder on a first side of the piston form a closed hydraulic circuit, which may also comprise connections between the cylinder and the reservoir, but as it is closed it is not in fluid communication with the cylinder at the other side of the piston. Valves are coupled in parallel between the reservoir and the hydraulic cylinder. A one-way valve (NL: terugslagklep) and a relief valve (NL: overdrukklep) may be used. The relief valve opens when the force on the mooring cable causes the pressure in the cylinder on the first side of the piston to exceed the pressure in the reservoir by more than a predetermined pressure threshold. Thus, the device provides slack on the mooring cable when the force on the cable exceeds a force threshold. When the force decreases, the one way valve opens, allowing liquid from the reservoir to push back the piston, to haul in the mooring cable.
As the one way valve and the relief valve may be passive mechanical devices that do not require external power to operate, the cable fastening device is very robust. The device may work without relying on external power supply while the ship is moored. Energy needed for hauling in is supplied by the force that pulls out the piston. Thus power consumption to keep a ship moored can be avoided. Instead of the one way valve and relief valve other combinations of valves may be used that provide for a similar difference between the pressure differences at which the valves open. The pressure difference at which the valve from the reservoir to the hydraulic cylinder opens determines the normal holding force and the pressure difference at which the valve from the hydraulic cylinder to the reservoir opens determines the maximum force on the cable. The predetermined threshold, which is determined by the difference between the pressure difference settings of the valves, may be at least ten Bar, more preferably at least fifty Bar or at least a hundred Bar and for example two-hundred Bar. The absolute value of the pressures is determined by the pressure in the reservoir which may be fifty Bar for example, or at least ten Bar.
In an embodiment the device may installed on a quayside, with one of the hydraulic cylinder and the piston attached to the quayside and the other one of the hydraulic cylinder and the piston attached to a ship via a cable. Thus, a port may provide facilities to protect ships against excessive forces on their cables.
In a further embodiment the device may be installed with a direction of movement of the piston in the hydraulic cylinder in parallel with the quay, the cable running from the device to the ship via a bollard on the quayside. In this way working space on the quay can be left free.
In an embodiment the device is provided with an auxiliary reservoir and a pump coupled between the auxiliary supply vessel and the hydraulic cylinder, on a second side of the piston, opposite said first side. This makes it easy to configure the mooring cables on mooring.
In a further embodiment the device comprises a control valve coupled between the auxiliary reservoir and the hydraulic cylinder, on the second side of the piston. The valve can be used to set an initial position of the piston on mooring.
In an embodiment the mooring device has an outer cylinder, the hydraulic cylinder being located within the outer cylinder, said closed reservoir comprising a space between the outer cylinder and the hydraulic cylinder. In this way a large reservoir can be provided without taking up much quayside space. The large reservoir helps to keep the maximum force independent of the position of the piston.
A mooring system may be provided that comprises a plurality of hydraulic mooring cable fastening devices according to the device according to any one of the preceding claims, installed along a quayside at a ships berth, each device having substantially the same predetermined threshold. Thus it is prevented that an excessive force will be placed on any one cable.

Brief description of the drawing

These and other objects and advantageous aspects will become apparent from a description of exemplary embodiments using the following figures.

Figure 1 shows a ship moored alongside a quay
Figure 2 shows a device for connecting a ship's cable
Figure 3 shows an embodiment of a device for connecting a ship's cable
Figure 4 shows a physical configuration of components on the device

Detailed description of an exemplary embodiment

Figure 1 shows a ship 10 moored alongside a quay 18 with a plurality of cables 12. On the quayside bollards 16 and hydraulic mooring devices 14 are provided. Hydraulic mooring devices 14 extend in parallel with the quayside. Each hydraulic mooring device 14 is attached at one end to the shore and on the other end to a respective one of the cables 12. Each cable 12 runs from a respective hydraulic mooring device 14 to ship 10 via a respective one of bollards 16.
Although four cables 12 have been shown by way of example, a greater number may be used in practice. The length of a berth for a ship along quay 18 may be from fifty to as long as four hundred meters or more. Although an embodiment has been shown wherein mooring devices 14 are installed on the quay, it should be appreciated that instead, or in addition they may be installed on board ship 10, or another type of mooring object such as a mooring buoy, a mooring turret etc. Typically, each cable 12 will be longer than the length of mooring device 14, so that yawing freedom of the ship left by an individual cable 12 plus mooring device 14 (disregarding the other cables) is determined substantially by the length of the cable 12 and substantially not by the mooring device 14. Mooring device 14.provides for rocking of the ship.
Figure 2 schematically shows one of the hydraulic mooring devices. The hydraulic mooring device comprises a piston 20 in a cylinder 22, a closed reservoir 24 for hydraulic liquid and gas, a one-way valve 25 coupled between reservoir 24 and cylinder 22 on a first side of piston 20, and a relief valve 26 coupled in parallel with one-way valve 25 between reservoir 24 and cylinder 22 on the first side of piston 20. Eyes 20a, 22a, are provided on cylinder 22 and piston 20 for attachment to a ship's cable and the quayside. Although eyes are shown, it should be appreciated that other constructions for attachment to the cable and the quay may be used, such as hooks, pins etc.
One-way valve 25 is directed to block flow from cylinder 22 to reservoir 24, but to allow flow the other way when the pressure on the reservoir 24 side is higher than or equal to the pressure on the cylinder 22 side. Relief valve 26 is set to open when the pressure of the hydraulic liquid in cylinder 22 on the first side of piston 20 exceeds the pressure of the hydraulic liquid on the side of reservoir 24 by more than a preset pressure threshold value. A pressure difference threshold value of two-hundred Bar may be used for example. Relief valves are known per se. A relief valve may be realized for example as a spring loaded one way valve. Hydraulic liquid is provided in reservoir 24, but it is not entirely filled. Additional gas is provided in reservoir 24 at pressure. A residual gas pressure of fifty Bar may be used for example. During operation reservoir 24 and the part of cylinder 22 on the first side of piston 20 form a closed fluid system that includes their connections. No fluid enters this system or leaves to the outside during normal operation. Reservoir 24 may have a filling valve (not shown) for entering or removing hydraulic liquid and/or pressurizing gas in reservoir 24, but the filling valve is kept closed during normal operation.
In addition, the hydraulic mooring device is provided with a further reservoir 27, a pump 28, a one way valve 28a, and a valve 29. Pump 28 and valve 29 are coupled in parallel between further reservoir 27 and cylinder 22 on a second side of piston 20, with one way valve 28a coupled between pump 28 and cylinder 22, directed to block flow from cylinder 22 to pump 28. In operation the hydraulic mooring device 14 operates to provide slack to the cable 12 to ship 10 when the force on the cable exceeds a force threshold value and to haul in when the force drops below the force threshold value. The relevant forces are typically caused by rocking of ship 10 under the influence of wind gusts. A force on cable 12 results in a force on piston 20 that pulls piston 20 towards the side of cylinder 22 where relief valve 26 is connected. Typically this occurs when the superstructure of the ship tilts away from the quayside. When the resulting force is small, both valves 25, 26 to reservoir will remain closed. Relief valve 26 is set to open when the pressure of the hydraulic liquid in cylinder 20 exceeds the pressure of the hydraulic liquid on the side of reservoir 24 by more than a preset pressure threshold value (two hundred Bar for example). As a result, relief valve 26 will open when the force exerted by the cable 12 exceeds a threshold force, allowing hydraulic mooring device 14 to give slack on cable 10. When this happens, hydraulic fluid flows from cylinder 22 to reservoir 24.
Once the force decreases (typically when the ship rightens), the pressure difference between the hydraulic liquid in cylinder 20 and reservoir 24 will drop below the threshold. If the force decreases sufficiently this pressure difference will eventually reverse, causing one way valve 25 to open, which allows hydraulic liquid to flow back from reservoir 24 to cylinder 20. This produces a force on piston 20 to drive piston 20 away from the end of cylinder 20 on the first side of piston 20. This causes cable 12 to be pulled in, taking up the slack.
When the ship 10 is subject to a gale, the force peaks on the mooring cables 12 are mainly due to rocking of the ship, which has the effect that the superstructure of the ship moves away from the quayside and back. This kind of force peak can be relieved by giving a limited amount of slack, sufficient to allow for the rocking movement. As a result a limited stroke of the hydraulic mooring device 14, corresponding at least to this amount of slack, is sufficient to ensure that the force on the cable 12 will not exceed a maximum. The maximum force is determined by the relief pressure setting of relief valve 26. The maximum allowable force may depend on the type of cable 12 that is used. The pressure threshold setting is related to this force in proportion to the cross-sectional area of cylinder 22.
Although an embodiment with a one way valve from reservoir 24 to cylinder 22 and a check valve from cylinder 22 to reservoir 24 has been shown, it should be appreciated that other combinations of valves may be used to realize a similar effect. For example a one way valve could be used from cylinder 22 to reservoir 24 to open when the pressure in cylinder 22 is higher than that in reservoir 24 due to a force on the cable, and a check valve from reservoir 24 and cylinder 20 to open when the pressure in reservoir 24 is more than a threshold higher than that in cylinder 22 due to a drop in force on the cable. However, in this case a higher pressure in reservoir 24 is needed to provide for the same maximum force. As an alternative, check values could be used in both directions between cylinder 22 and reservoir 24.
When a plurality of cables 12 is used, each coupled between ship 10 and a respective hydraulic mooring device 14, slack will be produced first on the cable 10 that is subject to the greatest force. This allows other cables 12 to take over part of the force. Preferably, all hydraulic mooring devices 14 that are used for the same ship are set to start providing slack from the same threshold force. This prevents that excessive forces are redirected to any one cable 12. The setting of relief valve 26 may be adjustable, to enable boatmen to set the force at mooring. Alternatively, a set of hydraulic mooring devices with predesigned substantially equal relief pressures may be used at a quayside. Preferably, hydraulic mooring devices 14 are used in combination with bollards 16, the cable running to the ship 10 from the hydraulic mooring device 14 via the bollard 16. This makes it possible to arrange the length of the hydraulic mooring device 14 along the quayside, leaving maximum space for harbor operation, without any need to rearrange the mooring system in anticipation of gales.
Further reservoir 27, pump 28, one way valve 28a and valve 29 are used temporarily to set the position of hydraulic mooring device 14 when the ship 10 is moored. Pump 28 may be used to drive piston 20 to a maximum position before mooring. When the ship has been brought along the quay, the cables 12 are coupled to the hydraulic mooring devices 14, hauled in and fastened on the ship 10. Next valve 29 may be opened, so that hydraulic pressure from reservoir 24 will drive back piston 20, taking up slack in cable 12 until the pressure due to hydraulic liquid from reservoir 24 equals the pressure due to force on cable 12. Valve 29 may be left open during further use. In this way forces that oppose hauling in the slack are avoided.
In an embodiment a stand alone system arrangement may be used wherein reservoir 27, pump 28, one way valve 28a, valve 29 are included in the hydraulic mooring device 14, optionally with an external mechanical, hydraulic or electric power connector to drive pump 28. This makes it to set the tension: simply and in a safe way by connection of the external mechanical hydraulic or electric power connection and activating the pump tension can be set. However, it should be appreciated that alternatively pump 28 and/or further reservoir 27 may be partly or fully detachable, so that they can be shared by different hydraulic mooring devices.
Figure 3 shows a design of the hydraulic mooring device 14 wherein reservoir 24 is realized in parallel with cylinder 22. The hydraulic mooring device 14 comprises an outer cylinder 30 and an inner cylinder 22, placed within outer cylinder 30. Piston 20 is included in inner cylinder 22. The space between outer cylinder 30 and inner cylinder 22 forms reservoir 24. This arrangement provides for a large size reservoir 24 with a minimum quayside occupation. The large size allows for a correspondingly large amount of pressurized gas in reservoir 24. This has the advantage that the maximum force on the cable 12 is hardly dependent on the position of piston 12.
Figure 4 shows a configuration with locations of the various components. In an embodiment, one way valve 26 and/or relief valve may be electronically controlled valves. However, it is preferred to use passive valves, i.e. valves that do not require any external power for there operation, such as known valves wherein the mechanical construction ensures one way operation and/or relief operation. No further energy input is needed during normal use. The energy needed to perform the work (pressure times piston stroke times piston area) needed to pull in the cable is supplied by the cable itself when it pulls out the piston and forces hydraulic fluid into the reservoir. No external energy supply is needed for this while the ship remains moored. This makes operation the hydraulic mooring device 14 highly robust.
In an embodiment the hydraulic mooring device 14 is provides with an electronic transmitter (e.g. a GSM or UMTS device or a transmitter for another type of communication channel) to transmit status information that allows mooring conditions to be monitored. For example, a detector may be provided for detecting whether piston 20 is driven out beyond a predetermined point on cylinder 22, and/or whether relief valve remains open for more than a predetermined amount of time. The detector may be configured to measure movement or position of the piston and to supply measured information to the electronic transmitter. In addition a pressure sensor may be provided, that measures pressure in the cylinder for example and supplies measurement results to the transmitter. The transmitter may be configured to transmit an alarm signal in response to detection that piston 20 is driven out beyond a predetermined point on cylinder 22, and/or whether relief valve remains open for more than a predetermined amount of time, to call for human intervention. The transmitter may be configured to supply measured information on request. It may comprise a memory and a controller to store measured information as a function of time for supply on request. Thus, mooring conditions can be remotely monitored.
A computer system may be provided with connections (e.g. wireless conditions) to the transmitters of different mooring cylinders, and a program with instructions to read out data from the plurality of mooring cylinders. Such a computer system may be provided for a port, to monitor mooring conditions in the port. Measurements may be read out from a plurality of mooring cylinders attached to mooring cables for the same ship for example, to evaluate or guard the mooring condition of the ship, or from mooring cylinders attached to mooring cables for a plurality of ships to monitor port conditions.
Preferably a transmitter for transmission to a remote location is provided for, that is a location outside the mooring device, for example to a location on the moored ship, or a computer network of the port. Preferably, the transmitter of each mooring device has a stored identity code, which allows individual mooring devices to be distinguished from each other, fro example by including the identity codes in the transmissions, or by allowing the identity code to be read out with the measurements. The computer network of the port may have a memory with stored information that links identity codes to quayside positions and information that links ships to quayside positions, or information that links identity codes directly to ships. Thus, the sensor data and/or alarms can be processed in combination with an identification of the ship.

Claims

A hydraulic mooring cable holding device for holding one end of a cable to a moored ship, the device comprising
- a hydraulic cylinder with a piston in the hydraulic cylinder;

- a reservoir with hydraulic liquid and gas, a part of the hydraulic cylinder on a first side of the piston and the reservoir forming an operationally closed hydraulic circuit;

- a first directional valve between the reservoir and the hydraulic cylinder on said first side of the piston, directed to selectively allow flow of the hydraulic liquid from the reservoir to the hydraulic cylinder,

- a second directional valve coupled between the reservoir and the hydraulic cylinder on said first side of the piston and directed to selectively allow flow of the hydraulic liquid from the hydraulic cylinder to the reservoir, the first and second directional valve being set to open at a first and second pressure difference from the hydraulic cylinder to the reservoir respectively, the second pressure difference exceeding the first pressure difference by a predetermined threshold.
A device as claimed in claim 1, wherein the first directional valve is a one way valve set to open substantially when pressure in the reservoir exceeds pressure in the hydraulic cylinder and the second directional value is a check valve set to open substantially when pressure in the hydraulic cylinder exceeds pressure in the reservoir by the predetermined threshold.
A device as claimed in claim 1 or 2, installed on a quayside, with one of the hydraulic cylinder and the piston attached to the quayside and the other one of the hydraulic cylinder and the piston attached to a ship via a cable.
A device as claimed in claim 3, installed with a direction of movement of the piston in the hydraulic cylinder in parallel with the quay, the cable running from the device to the ship via a bollard on the quayside.
A device according to any one of the preceding claims, comprising an auxiliary reservoir and a pump coupled between the auxiliary reservoir and the hydraulic cylinder, on a second side of the piston, opposite said first side.
A device according to claim 5, comprising a control valve coupled between the auxiliary reservoir and the hydraulic cylinder, on the second side of the piston.
A device according to any one of the preceding claims, comprising an outer cylinder, the hydraulic cylinder being located within the outer cylinder, said reservoir comprising a space between the outer cylinder and the hydraulic cylinder.
A device according to any one of the preceding claims, comprising at least one sensor for measuring a condition of the device and a transmitter coupled to the at least one sensor and configured to transmit sensor data and/or alarms based on sensor data to a remote location.
A device according to claim 8, wherein the at least one sensor includes at least one of a cylinder position detector and a hydraulic pressure sensor.
A system comprising a plurality of hydraulic mooring cable holding devices according to the device according to any one of the preceding claims, installed along a quayside at a ships berth, each device having substantially the same predetermined threshold.
A method of mooring a ship using a hydraulic reservoir with hydraulic liquid and gas and a hydraulic cylinder with a piston, the hydraulic reservoir and the hydraulic cylinder on a first side of the piston forming an operationally closed circuit for hydraulic fluid, the method comprising
- connecting a ship to a quayside via a cable and the piston and the hydraulic cylinder in series with each other;

- giving slack on the cable by automatically releasing hydraulic liquid from the hydraulic cylinder on said first side of a piston to the reservoir, selectively when a liquid pressure in the hydraulic cylinder due to force exerted by the cable exceeds a pressure in the reservoir by more than a first value;

- hauling in the cable by returning hydraulic liquid from the reservoir to the hydraulic cylinder on said first side of the piston selectively when a pressure in the reservoir exceeds a liquid pressure in the hydraulic cylinder by more than a second value, a difference between the first value and second value being equal to a predetermined positive threshold.
A method according to claim 11, the method comprising introducing hydraulic fluid into the cylinder on a second side of the piston, opposite the first side, coupling the ship to the quay via a ship's cable via the hydraulic cylinder and releasing the hydraulic fluid from the cylinder on said second side after the ship has been coupled to the quay to set an initial position of the piston.
A method according to claim 9 or 10, the method comprising using a plurality of hydraulic cylinders with a piston to moor a ship, each coupled between the ship and a quay via a respective cable, the thresholds being set substantially equal to each other for all hydraulic cylinders.