WO2022194852A1

WO2022194852A1 - Remote vessel-elevation survey system and method related thereto

Info

Publication number: WO2022194852A1
Application number: PCT/EP2022/056671
Authority: WO
Inventors: Line Sandager
Original assignee: Line Sandager
Priority date: 2021-03-16
Filing date: 2022-03-15
Publication date: 2022-09-22

Abstract

A system for measuring draft (4) of a vessel (20) is provided, the system comprising at least two positioning sensors (6,7), one of which is releasably mountable to the vessel (20), the other being arrangeable on a fix structure (5) separate from the vessel (20); an angle sensor (17) releasably mountable to the vessel (20); a sea level sensor (6, 8) mountable either on the vessel (20), or on the fix structure (5) separate from the vessel (20); and a control unit. The positioning sensors (6, 7) are configured to communicate in order to determine a relative elevation and/or lateral distance of the vessel positioning sensor (7) in relation to the fix structure positioning sensor (6); the angle sensor (17) is configured to determine an inclination angle of the vessel (20) in relation to the sea level; the sea level sensor (6, 8) is configured to determine a sea level distance between the sensor (6, 8) and the sea level; and the control unit is configured to calculate, by means of said relative elevation, said inclination angle, and said sea level distance, the draft (4) of the vessel (20) at any location along the vessel (20).

Description

REMOTE VESSEL-ELEVATION SURVEY SYSTEM AND METHOD RELATED THERETO

TECHNICAL FIELD

The present invention relates to a system for measuring draft of a vessel and a re lated method.

BACKGROUND

When referring to vessel draft (or draught) we refer to the depth of the vessel in the water. T raditionally this is determined by taking multiple (usually 6) points of visual measure, utilising markings where the sea meets the hull of the vessel.

Monitoring of draft is essential during the loading and discharge of cargo from a ves sel. It can be used, as is, to make sure the vessel does not reach the sea-bed. It is also used to calculate the weight of the vessel. This is achieved by combining draft data with vessel constants such as vessel length/breadth and calculated/measured variables such as ballast. Based on this the vessel displacement can be calculated which then provides the weight (by means of Archimedes' principle).

There are other associated advantages with determining draft, one of which is the improvement of load dynamics avoiding non-ideal trimming, causing aerodynamic and hydrodynamic environmental internal or external force, and hull stresses. It is thus concluded that an accurate draft measurement is important.

SUMMARY

The invention is defined by the appended independent claims. Additional features and advantages of the concepts disclosed herein are set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the described technologies. The features and advantages of the concepts may be realized and obtained by means of the instruments and combinations partic ularly pointed out in the appended claims. These and other features of the described technologies will become more fully apparent from the following description and ap pended claims, or may be learned by the practice of the disclosed concepts as set forth herein.

In a first aspect, a system for measuring draft of a vessel is provided. The system comprises at least two positioning sensors, one of which is releasably mountable to the vessel, the other being arrangeable on a fix structure separate from the vessel; an angle sensor releasably mountable to the vessel; a sea level sensor mountable either on the vessel, or on the fix structure separate from the vessel; and a control unit. The positioning sensors are configured to communicate in order to determine a relative elevation and/or lateral distance of the vessel positioning sensor in relation to the fix structure positioning sensor; the angle sensor is configured to determine an inclination angle of the vessel in relation to the sea level; the sea level sensor is configured to determine a sea level distance between the sensor and the sea level; and the control unit is configured to calculate, by means of said relative elevation, said inclination angle, and said sea level distance, the draft of the vessel at any lo- cation along the vessel.

In a second aspect, a method for measuring draft of a vessel is provided. The method comprises the steps of: providing a system for measuring draft of a vessel; - arranging at least two positioning sensors, of which at least one is ar ranged on the vessel and at least one is arranged on the fix structure separate from the vessel; arranging an angle sensor on the vessel; obtaining, by means of the positioning sensors, a relative elevation and/or lateral distance of the vessel positioning sensor in relation to the fix structure positioning sensor; obtaining, by means of the sea level sensor, a sea level distance be tween the sensor and the sea level; correcting, by means of the obtained sea level distance resulting from variations of the sea level, the relative elevation of the vessel positioning sensor; obtaining, by means of the angle sensor, an inclination angle of the vessel in relation to the sea level; calculating, by means of the control unit, a draft value for any location along the vessel by utilizing the relative elevation and the inclination angle of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to best describe the manner in which the above-described embodiments are implemented, as well as define other advantages and features of the disclosure, a more particular description is provided below and is illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the invention and are not therefore to be considered to be limiting in scope, the ex amples will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

Figure 1 Is a schematic of a ‘Fixed Sea-Level Sensor’ (FSS) attached to a fixed structure (wharf) to produce a sea-level (tide) reading Figure 2 is a schematic of two ‘Known Spatial Points’ (KSP) attached to a fixed struc ture (wharf)

Figure 3 is a front and above view of a vessel showing location of ‘Vessel Mounted Triangulation Sensors’ (VMTS) Figure 4a is an above view of a vessel showing the interaction of ‘Known Spatial Points’ (KSP) with Vessel mounted Thangulation Sensors’ (VMTS)

Figure 4b is a front vessel view showing the interaction of ‘Known Spatial Points’ (KSP) with Vessel mounted Triangulation Sensors’ (VMTS)

Figure 5 is a front and above view of a vessel showing location of ‘Vessel Mounted Depth Sensors’ (VMDS)

Figure 6 is a front and magnified view of a vessel showing attachment of a pressure sensor cable and ‘Data Transmission Node’ using a ‘S-shaped’ attachment unit.

Figure 7 is an above view of a vessel showing a magnified view of a stabilising collar and weight on a pressure sensor cable.

Figure 8a is a side view of a vessel, depicting the process of calculating a vessel ele vation at a chosen point, using a vessel angle as measured by a ‘Vessel Mounted Angle Sensor’ (VMAS) to extrapolate a specific elevation measurement measured by a ‘Vessel Mounted Depth Sensor’ (VMDS).

Figure 8b is a front and above view of a vessel, showing a combination of ‘Vessel Mounted Angle Sensor’ (VMAS) and ‘Vessel Mounted Depth Sensor’ (VMDS) to de rive Port and Starboard elevation data at chosen points.

Figure 9 is a flow diagram describing three embodiments of the invention.

Further, in the figures like reference characters designate like or corresponding parts throughout the several figures.

DETAILED DESCRIPTION

Various embodiments of the disclosed methods and arrangements are discussed in detail below. While specific implementations are discussed, it should be under stood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components, configurations, and steps may be used without parting from the spirit and scope of the disclosure.

In the description and claims the word “comprise” and variations of the word, such as “comprising” and “comprises”, does not exclude other elements or steps.

Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the inventive con cept. Other embodiments will be apparent to those skilled in the art from considera tion of the specification and practice disclosed herein. The embodiments herein are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept, and that the claims be construed as encompassing all equivalents of the present inventive concept which are apparent to those skilled in the art to which the inventive concept pertains. If nothing else is stated, different embodiments may be combined with each other.

The need to improve upon traditional draft survey is clear. There is a span of prior art that has addressed the problem in various ways. The invention described herein overcomes or at least mitigates various limitations in the prior art. It is a mobile unit allowing it to be utilised on any vessel compared to a fixed unit, one example of which is disclosed in CN104443299b. By capturing vessel angle data, the herein de scribed system is able to calculate multiple points of draft based on a single point of measure, improving on existing prior art capturing single point of measure via vari ous elevation measuring devices; pressure sensors as described in NL1029071 C2, ultrasonic sensor as described in CN2012200316157U, sonar as described in CN103661836A or GPS as described in AU2018248022A1. The herein described system has the advantage of minimising installation time by reducing the number of elevation measuring devices required and increasing ‘whole vessel’ draft accuracy by increasing the number of draft points. The system forms a ‘local position unit ar rangement’ meaning elevation data collection is completely independent of exterior data providers such as satellite, improving on the use of GPS. In addition, forming a ‘local position unit arrangement’ improves elevation real-time accuracy vs GPS, avoiding satellite related signal delays. The system compensates for sea level fluctu ations, unlike systems relying on fixed optical recognition, as described in AU2018248022A1. Yet another example of prior art is disclosed in AU2013268170B2.

The embodiments of this invention allow height from a fixed point on a vessel to be measured in relation to the sea-level, hereby referred to as elevation. By subtracting the elevation height from the known total height of the vessel the height under sea- level (draft) can be determined.

The embodiments described herein allow draft to be measured in the case that a vessel is berthed (tethered to a fixed structure such as a wharf) or in the case that it is at anchorage (away from a wharf). The importance of which is evident when the vessel loads away from the wharf via barge (a vessel carrying cargo from shore).

The detailed components of the described system used in various combination to achieve the described embodiments are: 1) Fixed Sea-Level Sensor (FSS); 2)

Known Spatial Points (KSP); 3) Vessel Mounted Triangulation Sensor (VMTS); 4) Vessel Mounted Depth Sensor (VMDS) 5); Vessel Mounted Angle Sensor (VMAS).

In one embodiment, the system comprises a ‘Fixed Sea-Level Sensor’ (FSS), Figure 1, the sensor being arranged on a fixed structure, fixed meaning not on the vessel and not changing elevation due to sea level structure, such as a wharf. Data from the FSS is used to determine the height of the sea level referred to as tide. The sensor generates data allowing change in sea height relative to the fixed sensor, examples of which are ultrasonic, radar, pressure tube, laser and mechanical.

Figure 1 shows: A Data Transmission Node (DTN) (1) receiving and transmitting from a ‘Fixed Sea-Level Sensor’ (2);

A ‘Fixed Sea-Level Sensor’ (FSS) (2): o which in this arrangement is a submerged pressure sensor, o and which is interchangeable with other apparatus able to measure distance from a fixed point to sea-level ‘X’ e.g. ultrasonic, radar, me chanical laser;

A pressure sensor (3) positioned below lowest sea-level, zeroed so that change in ‘X’ is measured;

Measure of sea-level ‘X’ (4);

A fixed structure (5) e.g. a wharf.

In one embodiment, the method comprises the steps of forming a local positioning unit arrangement, meaning all reference points within 5km diameter, allowing a unit with changing position to have its position, relative to fixed points, determined based on triangulation. With a minimum of three reference points required, at least one of which is at a fixed position and at least one of which is on the vessel.

In one embodiment, the method comprises the steps of forming ‘known spatial points’ (KSP) by fixing at least one positioning unit, Figure 2, capable of sending and/or receiving a signal to other positioning units, on a fixed structure such as a wharf. Fixed in this instance meaning not on the vessel and not changing elevation due to sea level. The KSP must be within communication distance of the vessel. These positioning units use signaling protocols such as WiFi, Bluetooth low-energy (BLE) beacons, Infra-red, ultrasonic, Long Range (LoRa), Long Range Wide Area Network (LoRaWAN) or any communication protocol which allows triangulation of other positioning units by measuring signal transmission and or return time between at least two other positioning units. The positioning unit/sensor is a unit/sensor capa ble of communicating with at least one other unit/sensor in order to determine its po sition. The positioning units/sensors are configured to only communicate with each other, in order to determine their mutual positions. Thus, a local positioning system is obtained.

Figure 2 shows:

- A fixed structure (5), e.g. a wharf;

- ‘Known Spatial Points’ (KSP) (6): o Fixed Transmitter/Receiving Units o Fixed horizontal and/or vertical from each other

- The sea.

In one embodiment, the method comprises the steps of forming a ‘Vessel Mounted Triangulation Sensor’ (VMTS), Figure 3, fixing to a vessel at least one positioning unit using a signaling protocol compatible with those used to create the ‘Known Spa tial Points’.

Figure 3 shows: Placement of ‘Vessel mounted triangulation sensors’ (VMTS) (7) in an exam ple arrangement.

In one embodiment, the method comprises the steps of determining the location, meaning horizontal distance and or vertical distance (elevation) relative to a KSP, of at least one VMTS by triangulation with two other positioning units including at least one KSP. Figure 4a & 4b Figure 4a shows an above vessel view:

‘Vessel mounted triangulation sensors’ (VMTS) (7) communicating with ‘Known Spatial Points’ (KSP) (6) to determine relative elevation of the VMTS (7) in relation to the KSP (6).

- ‘Known Spatial Points’ (KSP) (6): o Showing one arrangement where KSP (6) are horizontal from each other o In another arrangement KSP (6) may also be fixed vertical from each other o Or any combination of the two arrangements.

Figure 4b shows a front vessel view:

- ‘Known Spatial Points’ (KSP) (6): o Showing one arrangement where KSP (6) are vertical from each other o In another arrangement KSP (6) may also be horizontal from each other o Or any combination of the two arrangements ‘Vessel mounted triangulation sensors’ (VMTS) (7)

A fixed Structure (5) e.g. a wharf.

In one embodiment, the method comprises the steps of forming at least one ‘Vessel Mounted Depth Sensor’ (VMDS), Figure 5. The sensor is fixed to the vessel and ze roed. Meaning an arbitrary starting distance of zero is applied to the current meas urement between the fixed point and sea-level. This could then be corrected to a specific distance for example one related to the vessel draft lines as measured by a visual marine draft survey. As the vessel rises and falls in the water the sensor will capture this change relative to the zeroed point of reference, giving the change of elevation.

Figure 5 shows in a front vessel view and in a top vessel view:

Placement of ‘Vessel Mounted Depth Sensor’ (VMDS) (8) o In an example arrangement a ‘Vessel Mounted Angle Sensor’ (VMAS) (17) is utilised in combination.

In figure 5, ‘X’ = elevation or draft.

In one embodiment, the method comprises the steps of attaching the ‘Vessel Mounted Depth Sensor’ (VMDS) to the vessels railing, in one arrangement the VMDS is a pressure based depth sensor (pressure sensor), comprising of: 1) a control module; 2) a pressure sensor; 3) a cable. The cable transmits the pressure data and locates the pressure sensor. In one arrangement the pressure sensor is se cured to the vessel using a ‘cable-lock’ mechanism which grips the cable but does not damage the cable. In one arrangement an ‘s-shaped’ hook is used to attach the control module and ‘cable-lock’ to the vessel as well as provide a means to store ex cess cable. Figure 6

Figure 6 shows in a front vessel view and in a cross-section of ships railing:

- Railing (10)

‘S-shaped’ attachment unit (11)

Friction cable clamp attachment point (12)

- Cable (13)

Friction cable clamp (14)

Pressure sensor ‘Data Transmission Node’ (DNT) (1)

Looped excess cable (9)

In one embodiment, the method comprises the steps of stabilizing the ‘Vessel Mounted Depth Sensor’ (VMDS), in one arrangement the VMDS is a pressure sen sor having a cable connecting a control module (mounted on the vessels railing) to the sensor which is submerged in the sea. The sensor will experience force due to the sea current and the portion of the cable suspended in the air will experience wind force. For the sensor to accurately measure depth change due to the vessel, ideally it remains at a fixed vertical distance from the control module. To achieve this in one arrangement a weight is added to the cable, close to the sensor. In a second arrangement one or more ‘collars’ are added to the cable below water level, to pro vide an increased surface area in the horizontal plane and resist vertical movement. Figure 7

Figure 7 shows in a front vessel view:

Vessel Mounted Depth Sensor (VMDS) (8) o In this arrangement a pressure sensor

- Cable (13)

- Collar (15)

- Weight (16)

Pressure sensor (3)

Wind force Current force

Note that both current and wind force can be acting from any direction.

In one embodiment, the method comprises the steps of using at least one ‘Vessel Mounted Angle Sensor’ (VMAS), in a preferred arrangement this device is a gyro scope, mounted using removable fittings to a fixed position on the vessel, fixed meaning the movement measured by the gyroscope scope is due to the vessel not the gyroscope moving independent of the vessel. In an alternative embodiment, the vessel mounted angle sensor may be any device suitable for measuring an angle, such as, but not limited to, an accelerometer, theodolite, inclinometer, etc. This is used to determine the angle of the vessel relative to sea level and subsequent data such as list, trim, roll, pitch.

In one embodiment, the method comprises the steps of combining ‘Vessel Mounted Angle Sensor’ (VMAS) data with ‘Vessel Mounted Depth Sensor’ (VMDS) to calcu late the elevation of the vessel, at multiple points other than the points where spe cific VMDS data is captured. Figure 8a & 8b Figure 8a shows in a vessel side view:

Vessel Mounted Angle Sensor (VMAS) (17), determining angle of vessel rela- tive to sea-level (Z°)

Vessel Mounted Depth Sensor (VMDS) (8), determining distance from fixed point to sea-level, ‘X’ (Elevation)

Distance selected from VMDS where elevation is required.

Figure 8b shows in a vessel top view and a vessel front view:

- Vessel Mounted Depth Sensor (VMDS) (8): o Determining distance from fixed point to sea-level o Port side value Ύ’ o Starboard side value ‘X’

Vessel Mounted Angle Sensor (VMAS) (17), determining angle of vessel in relative to sea-level (Z°)

Using VMAS (17) + VMDS (8) data to determine elevation at chosen points: o In this arrangement VMAS (17) data (Z°) is used with VMDS (8) data (X) to calculate elevation on Starboard side o And VMAS (17) data (Z°) with VMDS (8) data (Y) on Port side.

In one embodiment, the method comprises the steps of combination of ‘Vessel Mounted Angle Sensor’ (VMAS) data with ‘Vessel Mounted Triangulation Sensor’ (VMTS) data to calculate the elevation of the vessel, at multiple points other than the points where VMTS data is specifically captured.

In one embodiment, the method comprises the steps of using the tide data gener ated by the ‘Fixed Sea-Level Sensor’ (FSS) to correct the data generated from the ‘Vessel Mounted Triangulation Sensor’ (VMTS). This is advantageous as the VMTS has measured total height which is composed of that: 1) due to sea-level, tide 2) due to vessel weight and its subsequent displacement. By subtracting the FSS tide data from the VMTS data determining the height due to vessel weight alone (elevation) is possible. In one embodiment, the method comprises the steps of using the elevation data generated to calculate, using known dimensions of the vessel and other required pa rameters such as water density, the vessel draft.

In one embodiment, the method comprises the steps of collecting elevation data at multiple points during the loading or discharging of a vessel, this in turn can be used to provide a change in draft measurement at time intervals and further a ‘live feed’ of vessel weight.

In one embodiment, the method comprises the steps of collecting elevation data at multiple points during the loading or discharging of a vessel, this may be used alone or in combination with ‘Vessel Mounted Angle Sensor’ data to determine changes in vessel angle at time intervals and further a ‘live feed’ of vessel angle.

In one embodiment, the method comprises the steps of optimising vessel position in the water. Whereby a combination of vessel angle data and or elevation/draft data are used to adjust the vessel, in one arrangement this provides improved fuel con sumption, lowered emissions, and a reduced risk of vessels structural stresses (avoiding associated environmental and economical impact resultant from hull fail ure).

In one embodiment, the method comprises the steps of forming a ‘Central Commu nication Hub’ (CCH), this hub would receive information from the ‘Data Transmission Nodes’ via an adequate communication protocol such as LoRaWAN, WiFi, Blue- Tooth. Raw Data received may be processed by a processing unit ‘computer’. Raw or processed data may then be transmitted to a cloud storage via an adequate com munication protocol such as WiFi or GSM connection to the internet.

In one arrangement the ‘Central Communication Hub’ (CCH) is a LoRaWAN gateway receiver device, mounted in a water-resistant enclosure and powered by a recharge able power source such as Lithium Polymer (LiPo) battery.

In one embodiment, the method comprises the steps of creating one or more ‘Data Transmission Nodes’ (DTN) linked to individual measuring devices, namely the Fixed Sea-Level Sensor (FSS); 2) Known Spatial Points (KSP); 3) Vessel Mounted Triangu lation Sensor (VMTS); 4) Vessel Mounted Depth Sensor (VMDS); 5) Vessel Mounted Angle Sensor (VMAS). These nodes would use a communication protocol to allow data captured to be communicated between nodes and to the Central Communica tion Hub.

In one embodiment, the method comprises the steps of forming a Cloud Storage Da tabase (CSD), as a depositary for raw data generated from the various points of measure, namely 1) Fixed Sea-Level Sensor (FSS); 2) Known Spatial Points (KSP);

3) Vessel Mounted Triangulation Sensor (VMTS); 4) Vessel Mounted Depth Sensor (VMDS); 5) Vessel Mounted Angle Sensor (VMAS). Additionally, processed data may be stored.

In one embodiment, the method comprises the steps of forming a User Interface, this would communicate to any combination of the following 1) Data Transmission Node (DTN); 2) Central Communication Hub (CCH); 3) Cloud Storage Database (CSD); 4) other exterior data sources such as those providing tidal, weather and ves sel data.

In one embodiment, the method comprises the steps of utilising the User Interface to control one or multiple points connected to a Data Transmission Node, namely the 1) Fixed Sea-Level Sensor (FSS); 2) Known Spatial Points (KSP); 3) Vessel Mounted Triangulation Sensor (VMTS); 4) Vessel Mounted Depth Sensor (VMDS); 5) Vessel Mounted Angle Sensor (VMAS). Examples of use would be collecting and receiving data, calibrating, zeroing or arranging interaction between the Data Transmission Nodes.

In one embodiment, the method comprises the steps of utilising the User Interface to monitor raw data collected from one or more Data Transmission Node (DTN) or the subsequent processed data or any combination of the two. This could be via a sum mary ‘dashboard’ or another visual representation such as graphs or data overlaid on a vessel schematic. It would display desired vessel metrics such as Angle,

Loaded Cargo Weight, Ballast etc.

Three specific embodiments of the system are given with reference to the figures. These are summarised in Figure 9.

EMBODIMENT No. 1: Determine at vessel elevation (draft) utilising; Known Spatial Points (KSP), Vessel Mounted Triangulation Sensor (VMTS), Vessel Mounted Angle Sensor (VMAS) and Fixed Sea-Level Sensor.

EMBODIMENT No. 2: Determine at vessel elevation (draft) utilising; Vessel Mounted Depth Sensor (VMDS) with Vessel Mounted Angle Sensor (VMAS).

EMBODIMENT No. 3 Determine at vessel elevation (draft) utilising; Known Spatial Points (KSP), Vessel Mounted Triangulation Sensor (VMTS), Vessel Mounted Angle Sensor (VMAS) and Vessel Mounted Depth Sensor (VMDS).

The various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Those skilled in the art will readily recognize various modifications and changes that may be made to the present in vention without following the example embodiments and applications illustrated and described herein, and without departing from the scope of the present disclosure.

Claims

1 . A system for measuring draft (4) of a vessel (20), the system compris ing: at least two positioning sensors (6, 7), one of which is releasably mountable to the vessel (20), the other positioning sensor being arrangeable on a fix structure (5) separate from the vessel (20), an angle sensor (17) releasably mountable to the vessel (20), a sea level sensor (6, 8) mountable either on the vessel (20), or on the fix structure (5) separate from the vessel (20), and a control unit; wherein the positioning sensors (6, 7) are configured to communicate in or der to determine a relative elevation and/or lateral distance of the vessel positioning sensor (7) in relation to the fix structure positioning sensor (6); wherein the angle sensor (17) is configured to determine an inclination an gle of the vessel (20) in relation to the sea level; wherein the sea level sensor (6,8) is configured to determine a sea level distance between the sensor (6, 8) and the sea level; and wherein the control unit is configured to calculate, by means of said relative elevation, said inclination angle, and said sea level distance, the draft (4) of the ves sel (20) at any location along the vessel (20).

2. The system according to any one of the preceding claims, comprising at least three positioning sensors (6, 7), one of which is releasably mountable to ei ther the vessel (20) or to the fix structure (5) separate from the vessel (20), the re maining positioning sensors (6, 7) being arrangeable on the other of the vessel (20) or the fix structure (5) separate from the vessel (20).

3. The system according to claim 2, wherein the positioning sensor(s) (7) arranged on the vessel (20) is arranged in a mid-portion of the vessel (20), on oppo site sides of the vessel (20).

4. The system according to any one of the preceding claims, wherein the positioning sensors (6, 7) are configured to form a local positioning system.

5. The system according to any one of the preceding claims, wherein the positioning sensors (6, 7) are triangulation sensors or sensors configured to perform local triangulation.

6. The system according to any one of the preceding claims, wherein the sea level sensor (8) is a level meter arranged on the fixed structure (5) separate from the vessel (20) and configured to measure a distance between the sensor (8) and the sea level.

7. The system according to any one of the preceding claims, wherein the sea level sensor (8) is a depth sensor releasably mountable on the vessel (20) on a fixed location in relation to the vessel (20) and configured to measure a distance be tween the fixed sensor location and the sea level.

8. The system according to any one of the preceding claims, wherein the fix structure (5) is any structure having a fixed level compared to the sea level, for example a wharf, a building, a land vehicle or a structure rigidly anchored to the sea bed.

9. The system according to any one of the preceding claims, wherein the system further comprises a communication unit for communicating the draft value to a display unit and/or a data storage means.

10. The system according to any one of the preceding claims, wherein the angle sensor (17) is one of a gyroscope, an accelerometer, or an inclinometer.

11. A method for measuring draft (4) of a vessel (20), the method compris ing the steps of: providing a system according to any one of the preceding claims; arranging at least two positioning sensors (6, 7), of which at least one is arranged on the vessel (20) and at least one is arranged on the fix structure (5) separate from the vessel (20); arranging an angle sensor (17) on the vessel (20); obtaining, by means of the positioning sensors (6, 7), a relative eleva tion and/or lateral distance of the vessel positioning sensor (7) in relation to the fix structure positioning sensor (6); obtaining, by means of the sea level sensor (6, 8), a sea level distance between the sensor (6, 8) and the sea level; correcting, by means of the obtained sea level distance resulting from variations of the sea level, the relative elevation of the vessel positioning sensor (7); obtaining, by means of the angle sensor (17), an inclination angle of the vessel (20) in relation to the sea level; calculating, by means of the control unit, a draft value for any location along the vessel (20) by utilizing the relative elevation and the inclination angle of the vessel (20).

12. The method according to claim 11 , wherein the method further com prises arranging the sea level sensor (8) on the vessel (20).

13. The method according to claim 11 or 12, wherein the method further comprises, during loading/unloading of the vessel (20), continuously obtaining val ues of the relative elevation and/or lateral distance, the sea level distance and the inclination angle, and calculating the draft value for any location along the vessel (20) at predetermined time intervals.