APPARATUS

The present invention relates to monitoring of offshore mooring arrangements and in particular, though not exclusively, to transmission of monitored data relating to offshore mooring

arrangements.

The oceans are becoming ever more important in the production of energy, from oil and gas production to offshore wind, tidal and wave power generation. As a result the number of substantial constructions related to these industries which need to be secured in marine environments is increasing. Floating structures, in water ranging from shallow to ultra-deep, can be secured using a variety of different techniques including single and multi-line mooring spreads. When mooring lines are used to secure a structure, each line can be sized and pre-tensioned to suit the requirements of the structure and the marine environment, including water depth, where it is deployed. However, marine environments can be harsh and the stresses, strains and wear and tear on the mooring lines need to be monitored to ensure that they are fit for purpose and operating within environmental and safety parameters which are deemed appropriate.

Systems for monitoring mooring lines have been developed to operate in marine environments.

ROV's with integrated sensors and monitors have been one mooring monitoring system developed wherein the ROV, carrying sensing equipment is connected to and launched from the anchored structure or a vessel associated with an anchored structure and explores the mooring lines detecting the mooring line status at that time. Whilst such systems provide good instant snapshots of the condition of the mooring line, the cable connected to the ROV is subject to the same harsh marine conditions as the mooring lines and therefore is also subject to wear, tear and damage. In addition, whilst these systems provide good data relating to a particular point in time, they do not provide an ongoing picture of the environment and condition of the mooring lines.

To overcome these drawbacks, cabled systems for monitoring mooring lines which are connected to, or integrated with, the mooring lines enables ongoing data to be obtained so that should any particular condition parameters be detected which are outside those which are deemed safe, an alarm system can be activated. This enables any potential weakness or failure in the mooring line to be addressed as and when they arise, or if environmental conditions appear to be likely to cause damage, appropriate precautions can be taken. Although these cabled systems provide ongoing data as to the condition of the mooring lines and the surrounding environments the cable connections are still weak points which can become damaged in the harsh marine environments meaning the monitoring systems can be unreliable.

Monitoring systems with acoustic wireless transmitters associated with the underwater detectors have been used to monitor mooring lines have reduced the need for fully cabled underwater systems, however acoustic signaling in marine environments has inherent difficulties due to the noise caused by reflections of the signal from surfaces and the Doppler effects which arise.

Therefore ensuring effective mooring monitoring data is provided reliably using a system relying upon acoustic transmission can be beset with difficulties due to the environment in which the mooring monitoring system is operating. It is an object of the present invention to provide a system and method for monitoring mooring lines which obviates or mitigates at least some of the disadvantages of the prior art.

According to a first aspect of the present invention there is provided a system for monitoring a mooring arrangement securing an offshore apparatus, the system comprising at least one detection mechanism operable to detect at least one characteristic of the mooring arrangement, at least one subsea communication unit associated with the mooring arrangement and operable to obtain data from the at least one detection mechanism, the at least one subsea communication unit including a wireless transmitter, and a master communication unit associated with the offshore apparatus, the master communication unit including a wireless receiver, operable to obtain data from the wireless transmitter of the at least one subsea communication unit wherein the at least one subsea communication unit and master communication unit are operable to communicate through a water and air boundary.

By having a monitoring system which enables wireless transmission of data relating to a characteristic of the mooring arrangement being monitored real time monitoring can be carried out and data transmitted accordingly. The facilitation of such real time data transmission ensures that swift and effective action can be taken should the data detected indicate that any change of condition has occurred which could adversely effect the functioning of the mooring arrangement. The mooring arrangement may comprise one or more mooring lines.

Preferably, the detection unit is provided with at least one sensor unit. The sensor unit may detect at least one characteristic of a mooring line. This arrangement facilitates the obtaining of characteristic data of the condition or environmental conditions surrounding the mooring line.

The detection unit may comprise a communication system for providing the detected data between the detection unit and the subsea communication unit.

Preferably, the detection unit and subsea communication unit are included in a monitoring unit. The detection unit, or the monitoring unit, may be integrally formed with a mooring line.

Integration of a detection unit, or a monitoring unit including a detection unit, into the mooring line facilitates the real time detection of any adverse changes of condition thus enabling swift and effective provision of such adverse changes to the master communication unit which can help ensure swift and effective action be taken to address the adverse change.

The detection unit, or the monitoring unit, may be located between a mooring line and the offshore apparatus.

The locating of a detection unit, or a monitoring unit including a detection unit, between the mooring line and the offshore apparatus facilitates the real time detection of any adverse changes of condition thus enabling swift and effective provision of such adverse changes to the master communication unit which can help ensure swift and effective action be taken to address the adverse change. The communication system may be a cable or wire. This arrangement is advantageous for arrangements where the detection unit and communication unit are located within a monitoring unit arrangement.

The communication system may alternatively comprise a transmitter and may comprise a receiver. Furthermore the communication system may alternatively comprise a transceiver.

Each subsea communication unit may comprise a transmitter and may comprise a receiver.

Furthermore, the subsea communication unit may comprise a transceiver.

Similarly, the master communication unit may comprise a transmitter and may comprise a receiver. Furthermore, the master communication unit may comprise a transceiver.

In this way, data may be wirelessly transmitted between the detection unit and the subsea communication unit. This arrangement is advantageous when the detection unit and the subsea communication unit are not formed integrally and therefore removes the requirement for an external cable connection between the two units.

Similarly, data may wirelessly be transmitted between the master communication unit and the subsea communication unit. Such an arrangement is advantageous as it removes the requirement of cabled or lossy acoustic transmission of data from the subsea communication unit to the master communication unit which is located at the air/water interface or above the water surface.

Preferably, each transmitter, receiver or transceiver has an electrically insulated magnetic coupled antenna. The antenna may be a wire loop, coil or similar arrangement. Such antenna creates both magnetic and electromagnetic fields. The magnetic or magento-inductive field is generally considered to comprise two components of different magnitude that, along with other factors, attenuate with distance (r) at rages proportional to 1/r ² and 1/r ³ respectively. Together they are often termed the near field components. The electromagnetic filed has a still different magnitude and, along with other factors, attenuates with distance at a rate proportional to 1/r. It is often termed the far field or propagating component.

Preferably, the data is transmitted as an electromagnetic and/or magneto -inductive signal.

Electromagnetic signals are rapidly attenuated in fluids which are electrically conductive in nature. Propagating radio waves are a result of an interaction between the electric and magnetic fileds. The high conductivity of a fluid will attenuate the electric field. The magnetic permeability of a material or fluid will affect the magnetic field. Water has a magnetic permeability close that of free space so there is little direct effect on the magnetic field component of a signal. Losses in electromagnetic signals are largely due to the effect of conduction on the electric field component. Propagating electromagnetic waves continually cycle energy between the electric and magnetic fields; hence conduction leads to strong attenuation of electromagnetic propagating waves. The attenuation losses in seawater provide a workable bandwidth which still provide for data transmission over a practical distance. Furthermore, the losses which occur in electromagnetic or magneto-inductive transmission over a water/air interface, as may be found between the subsea communication unit and the master communication unit, are negligible. This has the advantage of enable effective communication between the subsea communication unit and master communication unit. The data may be compressed prior to transmission. In this way the occupied transmission bandwidth can be reduced. This allows use of a lower carrier frequency which leads to lower attenuation. This in turn allows data transfer through the fluids over greater transmission distances.

Preferably, the subsea communication unit transceiver is operable to support inductive power transfer. This enables power to provided to the subsea communication unit without the need for battery exchanges or subsea contact power transfer both of which involve complex and costly operations.

The subsea communication unit and master communication unit may each further comprise acoustic transceivers. The inclusion of acoustic transceivers enables the use of hybrid

acoustic/electromagnetic communication between the subsea communication unit and master communication unit to provide an optimized communication system.

The subsea communication unit and master communication unit may each further comprise optical transceivers. The inclusion of optical transceivers enables the use of hybrid optical/electromagnetic communication between the subsea communication unit and master communication unit to provide an optimized communication system.

The subsea communication unit and master communication unit may each further comprise optical and acoustic transceivers. The inclusion of optical and acoustic transceivers enables the use of hybrid optical/acoustic/electromagnetic communication between the subsea communication unit and master communication unit to provide an optimized communication system.

According to a second aspect of the invention there is provided a method of monitoring a subsea mooring arrangement securing an offshore vessel, the method comprising the steps of:

a) detecting a data relating to a characteristic of the mooring arrangement using at least one detection unit;

b) providing said data to a subsea communication unit; and

c) transmitting said data from the subsea communication unit to a master communication unit;

wherein the master communication unit is located above sea.

Advantageously, the method of communication data relating to a characteristic of a mooring arrangement to a master communication unit enables the status of the mooring arrangement to be observed and managed.

Preferably, the detection unit provides the data to the subsea communication unit by one of electromagnetic and magneto-inductive transmission.

Preferably the subsea communication unit transmits the data to the master communication unit by one of electromagnetic and magneto-inductive transmission.

The use of electromagnetic and/or magento-inductive transmission facilitates effective

communication underwater and through the water/air boundary at the surface of the sea. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawing of which:

Figure 1A is a schematic illustration of a system for monitoring a mooring arrangement securing an offshore vessel according to an embodiment of the present invention;

Figure IB is a detail of an embodiment of a monitoring unit of the system of Figure 1A;

Figure 2 is a block diagram of a transceiver for use in the system of the present invention;

Figure 3 is a block diagram of an antenna for use in the transmitter or receiver of the transceiver of Figure 2;

Figure 4A is a schematic illustration of a system for monitoring a mooring arrangement securing an offshore vessel according to another embodiment of the present invention;

Figure 4B is a details of an embodiment of the mooring line arrangement of the system of Figure 4A;

Figure 5 is a schematic illustration of a system for monitoring a mooring arrangement securing an offshore vessel according to another embodiment of the present invention, and

Figure 6 is a schematic illustration of a system for monitoring a mooring arrangement securing an offshore vessel according to another embodiment of the present invention.

Reference is initially made to Figure 1A of the drawings which illustrates system for monitoring a mooring arrangement generally indicated by reference numeral 10, associated with an offshore apparatus which in this case is a boat 12. The system 10 is associated with the mooring arrangement 11 of the boat 12, the mooring arrangement 11 comprising mooring lines 14, in this case two mooring lines are shown, each of which is provided with an anchor 16. The mooring lines 14 extend from the boat 12, through the surface of the sea 18 to the seabed 20 where the anchors embed thus securing the boat 12. Monitoring units 22 are provided on mooring lines 14 with, in this case, two monitoring units 22 being provided on each mooring line 14. A master communication unit 30 is located on board the boat 12.

As can be seen in Figure IB, each monitoring unit 22 is formed integrally with the mooring line 14 and comprises a detection unit 24 and a subsea communication unit 26 which communicate with one another via communication system 25 which in this case is a cabled connection. However, it will be appreciated that in this case communication system 25 may be any suitable communication arrangement including, but not limited to an inductive arrangement, a socket connector or the like. The detection unit 24 includes a sensor unit 28 which detects at least one characteristic of the mooring line 14 including, but not limited to features such as tension, lateral force, rotational force, integrity and water current direction and speed. The subsea communication unit 26 is provided with at least one transmitter and/or receiver, in this case one transceiver 32 which transmit data through the water/air boundary 18 to the master communication unit 30 which is provided with least one transmitter and/or receiver, in this case one transceiver 33 which can receive the signals from the subsea communication unit 26. In use, the sensor unit 28 detects one or more predetermined characteristics and the detection unit 24 provides data relating to this characteristic to the subsea communication unit 26 via

communication system 25. The subsea communication unit 26 is then able to transmit data via wireless transceiver 32 which travels through the sea water, through the sea surface 18 and through the air to the master communication unit 30 where transceiver 33 receives the transmitted signals.

As monitoring system 10 which enables wireless transmission of data relating to a characteristic of the mooring lines 14, which are being monitored real time, the sensed data can be collected and transmitted accordingly. As the transmission of data may also be in real time, swift and effective action can be taken should the data received by master communication unit 30 indicate that a change of condition at or on the mooring 14 has occurred which could adversely effect the functioning of the mooring arrangement 11.

Reference is now made to Figure 2 of the drawings which illustrate parts of each transceiver 32, 33. In transceivers 32 the sensor interface 56 receives data from the sensor unit 28 which is forwarded to data processor 58. Data is then passed to signal processor 60 which generates a modulated signal which is modulated onto a carrier signal by modulator 62. Transmit amplifier 64 then generates the desired signal amplitude required by transmit transducer 66. In the transceiver 33, there is a control interface 52 which sends command signals to the data processor 58 which are transmitted by the above described path. The command signals can be used to detect the location of wireless transceivers 32.

The transceivers 32, 33 also have a receive transducer 70 which receives a modulated signal which is amplified by receive amplifier 72. De-modulator 74 mixes the received signal to base band and detects symbol transitions. The signal is then passed to signal processor 76 which processes the received signal to extract data. Data is then passed to processor 58 which in turn forwards the data to control interface 68. For the transceiver 33, there is also a memory 78 which can store data. Figure 3 shows and example of an antenna that can be used in the transmitter and receiver of Figure 2. This has a high permeability ferrite core 80. Wound round the core are multiple loops 82 of an insulated wire. The number of turns of the wire and length to diameter ratio of the core 80 can be selected depending on the application. However, for operation at 125kHz, one thousand turns and a 10:1 length to diameter ratio is suitable. The antenna is connected to the relevant

transmitter/receiver assembly parts described in Figure 2 and is included in a sealed housing 84. Within the housing, the antenna may be surrounded by air or some other suitable insulator 86, for example, low conductivity medium such as distilled water that is impedance matched to the propagating medium.

In use, the wireless transceiver 33 is located in the master communication unit 30 and the subsea wireless transceiver 32 is located in subsea communication unit 28. When data is provided to the subsea communication unit 28 by detection unit 22, the data is transmitted wirelessly between transceiver 32 to transceiver 33.

Reference is now made to Figures 4A and 4B of the drawings which illustrates another embodiment of the system 10. Like parts to those of Figure 1 have been given the same reference number to aid clarity. In this arrangement, the mooring lines 14 are provided with monitoring units 122 which are integrated into the mooring lines 14. Each mooring line 14 is also provided with a subsea communication unit 126. Each monitoring unit 122 is provided with a detection unit 124 which includes a sensor unit 128, and acoustic wireless transceiver 131 and an electromagnetic wireless transceiver 132. Each acoustic wireless transceiver 131 and an electromagnetic wireless transceiver 132 of monitoring unit 122 forms a communication system 125 with the subsea communication unit 126 which is similarly provided with acoustic wireless transceiver 131 and an electromagnetic wireless transceiver 132.

In use, when a sensor unit 28 detects one or more predetermined characteristics of the mooring line 14 recorded data is provided to one of the acoustic wireless transceiver 131 or electromagnetic wireless transceiver 132 depending on preset transmission criteria being met. The selected transceiver subsequently transmits the data to communication unit 126 where it is received by the corresponding acoustic wireless transceiver 131 or electromagnetic wireless transceiver 132. From there, the data is subsequently transmitted, from electromagnetic wireless transceiver 132 to the corresponding electromagnetic transceiver 133 on master communication unit 130. By using electromagnetic communication to transmit through sea surface 18, the integrity of the communicated data is better maintained thus ensuring more effective data commutation enabling more responsive monitoring of the mooring arrangement 11.

Reference is now made to Figure 5 of the drawings which illustrates another embodiment of the system 10. Like parts to those of Figure 1 have been given the same reference number to aid clarity. In this arrangement, the mooring lines 14 are provided with monitoring units 22. In this embodiment, the system 10 further includes a remotely operated vehicle (ROV) 90 which is connected to the vessel 12 by tether 92. The ROV 90 is provided with a transceiver 94 which comprises an antenna such as that detailed in Figure 2. The antenna can be used to magnetically couple energy between the transceivers 32 in monitoring units 22. In this regard, the housing 84 of the transceivers 94, 22 will act as a magnetic flux guide and the multiple loops 82 with the ferrite core 80 provide a transformer when a pair of transceivers are bought together such they are separated by an acceptable gap of only 1 - 2 cm. Thus, the range for power transfer is much smaller than the range for data communication. Coupling efficiency reduces as frequency increases because of leakage inductance effects. Eddy current losses increase with frequency so also act to reduce the bandwidth available for data transmission. Data and power transmission can be separated in frequency to allow simultaneous operation of the two functions. Transfer efficiency is more critical for power transfer than for data communication applications so a higher frequency will usually be assigned to the data communication signals. While the transceivers 32, 94 have been described with a common antenna for transmit and receive, separate antennas may be used. Additionally, a separate transmitter coil arrangement can be provided solely for power transfer. In this way, power can be transmitted from the ROV 90 to a battery (not shown) which supplies power to the monitoring unit 22. Furthermore, should a problem occur where transmission of data between monitoring unit 22 and master communication unit 30 has failed, the ROV can also act to collect data from and provide data to the monitoring unit 22. Any collected data can then be downloaded from the ROV. It will be appreciated that as opposed to an ROV, data and power may be transmitted and received to the monitoring units 22 from an AUV (not shown) or a diver carrying power and data transmitting equipment (not shown).

Reference is now made to Figure 6 of the drawings which illustrates another embodiment of the system 10. Like parts to those of Figure 1 have been given the same reference number to aid clarity. In this arrangement, the mooring lines 14 extend from an undersea area 12a of vessel 12. The mooring lines 14 are secured to the undersea area 12a by monitoring units 22. Each monitoring unit 22 comprises a detection unit 24 and a subsea communication unit 26 which communicate with one another via communication system 25 such as that shown in Figure IB. However, it will be appreciated that in this case communication system 25 may be any suitable communication arrangement including, but not limited to an inductive arrangement, a socket connector or the like.

In use, when detection unit 24 detects one or more predetermined characteristics of the mooring line 14 at the connection between the mooring line and the vessel 12 where the monitor unit 22 is located, recorded data is provided to the communication unit 26 from where it is transmitted using electromagnetic wireless transmission to the master communication unit 130. By using electromagnetic communication to transmit through sea surface 18, the integrity of the communicated data is better maintained thus ensuring more effective data commutation enabling more responsive monitoring of the mooring arrangement 11. This arrangement is particularly suited to offshore vessels 12 provided with a moon pool (not shown).

The principle advantage of the present invention is that real time data can be collected from a subsea mooring arrangement of an offshore vessel and provided to a master unit located above sea level to enable expedient action should any operational or conditional parameters of the mooring arrangement be exceed.

A further advantage of the present invention is that the system provides a wireless arrangement for monitoring a mooring arrangement.

A yet further advantage of the present invention is that the system provides a wireless arrangement for the monitoring of a mooring arrangement wherein subsea components can be provided with power using the same wireless components.

It will be appreciated by those skilled in the art that various modifications may be made to the invention as herein before described without departing to the scope thereof. For example, the vessel 12 has been described as a boat, however the vessel may alternatively be a wind turbine, a tidal power or wave power harnessing arrangement or an oil industry vessel. In addition, while the monitoring units 22, 122 have been described as being integral with the mooring lines 14, they may instead be attached or secured to the mooring lines 14. Similarly, whilst the mooring lines have been described as each being provided with two mooring monitoring units 22, each mooring line 14 may be provide with any number of monitoring units 22 arranged in a daisy chain type arrangement whereby they can communicate with one another and passing information up and down adjacent monitoring units to and from the vessel.