Non-dynamic draught detection system and method for ship

Abstract

The invention belongs to the field of ship detection, and particularly relates to a non-dynamic draught detection system and method of a ship, the system comprises a base station, a tide level station, a plurality of mobile stations and an acquisition and control terminal, the base station is used for calculating an error value between a real-time observation coordinate and a known accurate coordinate; transmitting differential data including the error value to the mobile station; the tide level station is used for continuously monitoring real-time tide level data of the sea area where the ship is located. The mobile station is used for receiving the GNSS satellite signal and the differential data sent by the base station, and resolving to obtain a three-dimensional coordinate; measuring the offset of the mounting position of the mobile station and the vertical direction of the freeboard deck; and the acquisition and control terminal is used for receiving the three-dimensional coordinates and the offset in the vertical direction of each mobile station, calculating the barycentric coordinates of the freeboard deck by adopting a three-point barycentric algorithm according to the plane coordinates and the calibration elevation of the three mobile stations, obtaining the actual height of the water surface where the ship is located, and calculating the real-time draft of the ship. According to the draught detection system, efficient, convenient and accurate ship draught detection can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of ship inspection technology, specifically relating to a non-dynamic draft detection system and method for ships. Background Technology

[0002] Ship draft monitoring is a fundamental aspect of ensuring navigational safety, compliant operation, optimizing transportation efficiency, and maintaining the shipping ecosystem. It spans the entire lifecycle of a ship, providing crucial data support for ship operation and management. Currently, ship draft measurement mainly involves two methods: manual reading and instrument / equipment measurement, specifically including the following main technical means: Manual reading combined with float-state calculation: This is the most traditional and widely used method for draft measurement. Surveyors read draft data (six-sided draft data) from the draft gauges placed on both sides of the ship's bow, midships, and stern. Then, based on different float states such as upright, trim, and yaw, the average draft is calculated using formulas. For example, the draft is consistent when the ship is upright; when trimmed, corrections are needed based on the ship's length between perpendiculars and the distance from the center of float to midships; when yaw exists, a simplified formula (d_F + d_A + 6 × d_M) / 8 is commonly used for calculation. This method is low-cost and easy to implement, but it suffers from low measurement accuracy and efficiency, is highly susceptible to human factors, and the results lack objectivity, easily leading to disputes.

[0003] Precise Sonar Measurement: This method is suitable for automated monitoring in ports, waterways, and other similar scenarios, calculating draft based on the principle of sound wave reflection. Taking the side-scan sonar method as an example, sonar equipment is installed at the bottom of the waterway, continuously emitting sound beams. When a ship passes by, the echo signal from the hull is received. By analyzing the echo positions of characteristic points such as the intersection of the hull and the water surface, and the bilge, combined with the sonar installation depth, horizontal distance, and hull line parameters, a geometric equation is constructed to solve for the draft. This type of method has high accuracy, but the equipment must be installed underwater, making it susceptible to seawater corrosion and siltation, resulting in high maintenance costs. Furthermore, surface waves significantly interfere with measurement accuracy.

[0004] This method, based on the theory of ship weight and buoyancy, relies on Archimedes' principle, assuming that the ship's buoyancy equals its total weight. Draft is then calculated using the formula h = W / (ρ×L×B) (where W is the ship's total weight, ρ is the density of water, L is the length of the waterline, and B is the width of the waterline). While simple in principle, this method fails to consider variations in actual hull lines and is only suitable for rough estimations of regular ship types such as flat-bottomed vessels. Furthermore, since in shipping practice, it's often necessary to deduce load capacity from draft, this method represents a reversal of cause and effect, resulting in poor practicality. Moreover, changes in seawater salinity and temperature significantly impact the calculation results.

[0005] Ultrasonic phased array technology: This method uses a one-dimensional linear ultrasonic phased array transducer to emit focused acoustic waves to scan the hull. Matched filtering and thresholding algorithms are used to extract the echo signal delay. The upper and lower boundaries of the underwater profile of the hull are determined using the transit time method and the hyperbolic intersection method, thus deriving the draft. The maximum relative error can be controlled within 2%. This method is suitable for high-precision monitoring of inland waterway vessels, but the system is complex and its practical application is limited.

[0006] Image-processing-based water level gauge detection: In recent years, with the development of image processing technology, the automatic reading of water level gauges using image recognition technology has gradually emerged. This method has the advantages of being non-contact and highly efficient, but it is subject to many limitations due to conditions such as lighting, water quality, and ship cleanliness in the application scenario. Furthermore, the portability and integration of the equipment are poor, which limits its large-scale promotion.

[0007] Calculation methods based on high-precision differential positioning technology: High-precision differential positioning technology (including RTK and PPP) has been applied to ship draft measurement. RTK (Real-Time Kinematic) is based on real-time communication between a shore-based reference station and a shipborne rover station, achieving centimeter-level elevation measurement through differential correction, and then inferring the draft, with an accuracy of 0.1~0.3 meters. PPP (Precise Point Positioning), on the other hand, does not require a shore-based reference station; it achieves high-precision single-point positioning by receiving precise ephemeris data broadcast by satellite, making it suitable for ocean-going vessels.

[0008] However, existing GNSS (Global Navigation Satellite System) based draft measurement solutions still have the following shortcomings: First, rover stations are usually fixed to specific vessels and owned by the shipowner, making it difficult for port authorities to trust the authenticity and reliability of their data, resulting in the continued widespread use of manual draft readings; Second, existing solutions rely on attitude sensors to correct pitch / roll deviations, making the system complex and costly to install, which is unacceptable for small and medium-sized vessels, while integrating existing equipment on large vessels is difficult; Third, as a single-point device, the rover station has stringent requirements for its installation location, needing to consider both signal reception and hull layout, making it difficult to form a unified solution.

[0009] There is an urgent need for an objective, efficient, low-cost draft detection solution suitable for ships berthing in ports. Summary of the Invention

[0010] To achieve objective, efficient, low-cost, and applicable draft detection for ships berthing in ports, this application provides a non-dynamic draft detection system and method for ships.

[0011] In a first aspect, embodiments of this application provide a non-dynamic draft detection system for ships, the system comprising a base station, a tide station, multiple mobile stations, and a data acquisition and control terminal, wherein the number of mobile stations is 3 to 6. The base station is fixedly set at a land location with known precise coordinates. It is used to receive GNSS satellite signals, calculate real-time observation coordinates based on the GNSS satellite signals, and calculate the error value between the real-time observation coordinates and the known precise coordinates. It then sends differential data including the error value to the rover station. The tide level station is used to continuously monitor the real-time tide level data of the sea area where the ship is located and send the tide level data to the acquisition and control terminal. The mobile station is used to receive GNSS satellite signals and differential data sent by the reference station, calculate centimeter-level three-dimensional coordinates with the reference station as the origin, measure the vertical offset between the installation position of the mobile station and the freeboard deck using a laser ranging module, and send the three-dimensional coordinates and the vertical offset to the data acquisition and control terminal. The multiple mobile stations are deployed at different positions on the ship's freeboard deck, and their deployment purpose is to enable the data acquisition and control terminal to determine the center of gravity of the ship's deck through geometric relationships based on their coordinate data. The deployment positions of the multiple mobile stations satisfy the following: there are two mobile stations deployed on the same side of the ship, and there is a third mobile station deployed in the opposite area to that side, the opposite area including the other side, the bow, or the stern. The acquisition and control terminal is used to receive the three-dimensional coordinates and vertical offset sent by each mobile station, subtract the difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset to obtain the calibration elevation of each mobile station on the deck plane, calculate the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the plane coordinates and calibration elevations of the three mobile stations, receive the tide level data sent by the tide level station, and calculate the actual height of the ship in the water based on the tide level data and the known elevation information of the reference station, and calculate the real-time draft of the ship based on the elevation in the centroid coordinates, the water level height, and the ship's draft depth.

[0012] In one possible implementation, when the plurality of mobile stations include two mobile stations on the same side and one mobile station on the other side, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two calibrated mobile stations on the other side as the vertex, and the mobile station with the longest side formed with the vertex among the two calibrated mobile stations on the same side as the other vertex.

[0013] In one possible implementation, when the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern on the centerline of the ship, the acquisition and control terminal is used to calculate the center-of-gravity coordinates of the freeboard deck based on the difference in calibration elevations of the two calibrated mobile stations on the same side, the calibration elevation of one of the calibrated mobile stations, the calibration elevation of the third mobile station, and the planar coordinates of the three mobile stations.

[0014] In one possible implementation, when the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern off the centerline, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two mobile stations on the same side with the longest side formed with the calibrated bow / stern off the centerline as the vertex, and the calibrated bow / stern off the centerline as the other vertex.

[0015] In one possible implementation, calculating the ship's real-time draft based on the elevation, water level, and ship depth in the centroid coordinate system includes: The height of the deck's center of gravity above the water surface is obtained from the elevation and water level in the center of gravity coordinates. The draft of a ship is determined by subtracting the height of the deck's center of gravity from the waterline from the ship's hull depth.

[0016] Secondly, embodiments of this application provide a non-dynamic draft detection method for ships, the method comprising: The system receives GNSS satellite signals from a base station fixed at a land location with known precise coordinates, calculates real-time observation coordinates based on the GNSS satellite signals, and calculates the error value between the real-time observation coordinates and the known precise coordinates; then it sends differential data including the error value to the mobile station. The real-time tide level data of the sea area where the ship is located is continuously monitored by the tide level station, and the tide level data is sent to the acquisition and control terminal. The mobile station receives GNSS satellite signals and differential data transmitted by the base station, and calculates centimeter-level three-dimensional coordinates with the base station as the coordinate origin. A laser ranging module measures the vertical offset between the mobile station's installation position and the freeboard deck, and the three-dimensional coordinates and the vertical offset are transmitted to the data acquisition and control terminal. Multiple mobile stations are deployed at different locations on the ship's freeboard deck. Their deployment aims to enable the data acquisition and control terminal to determine the ship's deck center of gravity based on its coordinate data and geometric relationships. The deployment positions of the multiple mobile stations satisfy the following conditions: two mobile stations are deployed on the same side of the ship, and a third mobile station is deployed in the opposite area, including the other side, the bow, or the stern. The number of mobile stations is 3 to 6. The acquisition and control terminal receives the three-dimensional coordinates and vertical offset sent by each mobile station. The difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset is subtracted to obtain the calibration elevation of each mobile station on the deck plane. Based on the plane coordinates and calibration elevation of the three mobile stations, the centroid coordinates of the freeboard deck are calculated using the three-point centroid algorithm. The tidal data sent by the tidal station is received, and the actual height of the ship in the water is calculated based on the tidal data and the known elevation information of the reference station. Based on the elevation in the centroid coordinates, the water surface height, and the ship's draft, the real-time draft of the ship is calculated.

[0017] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station on the other side, the step of calculating the center-of-gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station on the other side as the vertex, the mobile station with the longest side formed with the calibrated mobile station on the same side is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

[0018] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern along the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated rover station at the bow / stern of the ship's centerline as the vertex, and the rover station with the longest side formed with the calibrated rover station on the same side as the other vertex, the coordinates of the center of gravity of the freeboard deck are calculated based on the difference in calibration elevations of the two vertices, the calibration elevation of one of the vertices, the calibration elevation of the third rover station, and the planar coordinates of the three rover stations.

[0019] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern not on the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station at the bow / stern (not on the centerline) as the vertex, the mobile station with the longest side formed by the two calibrated mobile stations on the same side as the calibrated mobile station is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

[0020] Thirdly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any of the above-described methods for non-dynamic draft detection of ships.

[0021] This application provides a non-dynamic draft detection system for ships. The system includes a base station, a tide level station, multiple mobile stations, and a data acquisition and control terminal. The number of mobile stations is 3 to 6. The base station is fixedly installed at a land location with known precise coordinates. It receives GNSS satellite signals, calculates real-time observation coordinates based on the GNSS satellite signals, and calculates the error value between the real-time observation coordinates and the known precise coordinates. It then sends differential data including the error value to the mobile stations. The tide level station continuously monitors real-time tide level data in the sea area where the ship is located and sends the tide level data to the data acquisition and control terminal. The mobile stations receive the GNSS satellite signals and the differential data sent by the base station, calculate centimeter-level three-dimensional coordinates with the base station as the coordinate origin, and measure the vertical offset between the installation position of the mobile station and the freeboard deck using a laser ranging module. The three-dimensional coordinates and the vertical offset are then sent to the data acquisition and control terminal. The multiple mobile stations... The multiple mobile stations are deployed at different locations on the ship's freeboard deck. Their purpose is to enable the data acquisition and control terminal to determine the ship's deck center of gravity based on its coordinate data and geometric relationships. The deployment positions of the multiple mobile stations satisfy the following conditions: two mobile stations are deployed on the same side of the ship, and a third mobile station is deployed in the opposite area to that side, including the other side, the bow, or the stern. The data acquisition and control terminal is used to receive the three-dimensional coordinates and vertical offset sent by each mobile station, subtract the corresponding vertical offset from the elevation value in the three-dimensional coordinates to obtain the calibration elevation of each mobile station on the deck plane, calculate the center of gravity coordinates of the freeboard deck using a three-point center of gravity determination algorithm based on the plane coordinates and calibration elevations of the three mobile stations, receive the tide level data sent by the tide level station, and calculate the actual height of the ship in the water based on the tide level data and the known elevation information of the reference station. Based on the elevation in the center of gravity coordinates, the water level height, and the ship's draft, the real-time draft of the ship is calculated. The draft detection system described in this application enables efficient, convenient, and accurate ship draft detection. Attached Figure Description

[0022] Figure 1 A schematic diagram of a non-dynamic draft detection system for a ship provided in an embodiment of this application; Figure 2 A schematic diagram showing the deployment locations and signal coverage of the base station and data acquisition and control terminal; Figure 3(i) is a schematic diagram of the first deployment method of the mobile station; Figure 3(ii) is a schematic diagram of the first method for calculating the center of gravity of a mobile station; Figure 4(i) is a schematic diagram of the second deployment method of the mobile station; Figure 4(ii) is a schematic diagram of the second method for calculating the center of gravity of the mobile station; Figure 5(i) is a schematic diagram of the third deployment method of the mobile station; Figure 5(ii) is a schematic diagram of the third method for calculating the center of gravity of a mobile station; Figure 6 This is a schematic diagram illustrating the system composition and information transmission relationships in the embodiments of this application; Figure 7 This is a schematic diagram of the internal structure of the base station; Figure 8 This is a schematic diagram of the internal structure of the mobile station; Figure 9 This is a schematic diagram of the internal structure of the tide gauge station; Figure 10 This is a schematic diagram of the internal structure of the data acquisition and control terminal; Figure 11 This is a schematic diagram for calculating the waterline. Detailed Implementation

[0023] The present invention will be described in detail below through embodiments.

[0024] Ship draft monitoring is a fundamental aspect of ensuring navigational safety, compliant operation, optimizing transportation efficiency, and maintaining the shipping ecosystem. It spans the entire lifecycle of a ship, providing crucial data support for ship operation and management. Currently, ship draft measurement mainly involves two methods: manual reading and instrument / equipment measurement, specifically including the following main technical means: Manual reading combined with float-state calculation: This is the most traditional and widely used method for draft measurement. Surveyors read draft data (six-sided draft data) from the draft gauges placed on both sides of the ship's bow, midships, and stern. Then, based on different float states such as upright, trim, and yaw, the average draft is calculated using formulas. For example, the draft is consistent when the ship is upright; when trimmed, corrections are needed based on the ship's length between perpendiculars and the distance from the center of float to midships; when yaw exists, a simplified formula (d_F + d_A + 6 × d_M) / 8 is commonly used for calculation. This method is low-cost and easy to implement, but it suffers from low measurement accuracy and efficiency, is highly susceptible to human factors, and the results lack objectivity, easily leading to disputes.

[0025] Precise Sonar Measurement: This method is suitable for automated monitoring in ports, waterways, and other similar scenarios, calculating draft based on the principle of sound wave reflection. Taking the side-scan sonar method as an example, sonar equipment is installed at the bottom of the waterway, continuously emitting sound beams. When a ship passes by, the echo signal from the hull is received. By analyzing the echo positions of characteristic points such as the intersection of the hull and the water surface, and the bilge, combined with the sonar installation depth, horizontal distance, and hull line parameters, a geometric equation is constructed to solve for the draft. This type of method has high accuracy, but the equipment must be installed underwater, making it susceptible to seawater corrosion and siltation, resulting in high maintenance costs. Furthermore, surface waves significantly interfere with measurement accuracy.

[0026] This method, based on the theory of ship weight and buoyancy, relies on Archimedes' principle, assuming that the ship's buoyancy equals its total weight. Draft is then calculated using the formula h = W / (ρ×L×B) (where W is the ship's total weight, ρ is the density of water, L is the length of the waterline, and B is the width of the waterline). While simple in principle, this method fails to consider variations in actual hull lines and is only suitable for rough estimations of regular ship types such as flat-bottomed vessels. Furthermore, since in shipping practice, it's often necessary to deduce load capacity from draft, this method represents a reversal of cause and effect, resulting in poor practicality. Moreover, changes in seawater salinity and temperature significantly impact the calculation results.

[0027] Ultrasonic phased array technology: This method uses a one-dimensional linear ultrasonic phased array transducer to emit focused acoustic waves to scan the hull. Matched filtering and thresholding algorithms are used to extract the echo signal delay. The upper and lower boundaries of the underwater profile of the hull are determined using the transit time method and the hyperbolic intersection method, thus deriving the draft. The maximum relative error can be controlled within 2%. This method is suitable for high-precision monitoring of inland waterway vessels, but the system is complex and its practical application is limited.

[0028] Image-processing-based water level gauge detection: In recent years, with the development of image processing technology, the automatic reading of water level gauges using image recognition technology has gradually emerged. This method has the advantages of being non-contact and highly efficient, but it is subject to many limitations due to conditions such as lighting, water quality, and ship cleanliness in the application scenario. Furthermore, the portability and integration of the equipment are poor, which limits its large-scale promotion.

[0029] Calculation methods based on high-precision differential positioning technology: High-precision differential positioning technology (including RTK and PPP) has been applied to ship draft measurement. RTK (Real-Time Kinematic) is based on real-time communication between a shore-based reference station and a shipborne rover station, achieving centimeter-level elevation measurement through differential correction, and then inferring the draft, with an accuracy of 0.1~0.3 meters. PPP (Precise Point Positioning), on the other hand, does not require a shore-based reference station; it achieves high-precision single-point positioning by receiving precise ephemeris data broadcast by satellite, making it suitable for ocean-going vessels.

[0030] However, existing GNSS (Global Navigation Satellite System) based draft measurement solutions still have the following shortcomings: First, rover stations are usually fixed to specific vessels and owned by the shipowner, making it difficult for port authorities to trust the authenticity and reliability of their data, resulting in the continued widespread use of manual draft readings; Second, existing solutions rely on attitude sensors to correct pitch / roll deviations, making the system complex and costly to install, which is unacceptable for small and medium-sized vessels, while integrating existing equipment on large vessels is difficult; Third, as a single-point device, the rover station has stringent requirements for its installation location, needing to consider both signal reception and hull layout, making it difficult to form a unified solution.

[0031] There is an urgent need for an objective, efficient, low-cost draft detection solution suitable for ships berthing in ports.

[0032] Therefore, the main objective of this invention is: First, it provides port and shipping authorities with an objective and accurate method for measuring the non-dynamic draft of vessels in port, replacing manual labor and significantly improving work efficiency, achieving near real-time monitoring (second-level).

[0033] Second, reduce reliance on other sensors and invent a relatively independent ship draft measurement device.

[0034] Third, the functions are broken down to improve the portability of mobile stations and achieve efficient deployment and measurement.

[0035] Fourth, reduce reliance on specific ships and invent a universal method for measuring ship draft.

[0036] Fifth, it provides a multi-redundancy design to avoid single-point failures and reduce the probability of measurement failure.

[0037] In a first aspect, embodiments of this application provide a non-dynamic draft detection system for ships, the system comprising a base station 101, a tide station 102, multiple mobile stations 103, and a data acquisition and control terminal 104, wherein the number of mobile stations is 3 to 6. The base station 101 is fixedly set at a land location with known precise coordinates. It is used to receive GNSS satellite signals, calculate real-time observation coordinates based on the GNSS satellite signals, and calculate the error value between the real-time observation coordinates and the known precise coordinates. It then sends differential data including the error value to the rover station. In the fields of GNSS satellite navigation and surveying, "solution" is a specific term. It describes the entire process of calculating the real-time observed coordinates of a base station from the received raw satellite signals (carrier phase, pseudorange, etc.) through a series of complex algorithms and models (such as error elimination and ambiguity fixing). The base station transmits differential data, including the error values ​​between the real-time observed coordinates and the known precise coordinates, to the rover station in real time via wireless communication (such as 4G / 5G, microwave). Since there are unified specifications and standards for base station differential data transmission, it is not necessary to build new base stations; it is sufficient to use existing data directly according to the specifications.

[0038] The tide station 102 is used to continuously monitor the real-time tide data of the sea area where the ship is located and send the tide data to the acquisition and control terminal. Like reference stations, tide gauge stations are built at fixed locations on land. They are core infrastructure for marine hydrological monitoring, with the primary function of providing long-term, continuous, and accurate monitoring of hydrological data such as tidal changes in the area. Tidal data can also be linked with ship positioning and draft measurement data to enhance the completeness of ship monitoring. Tidal gauge stations are also common port facilities and can therefore be directly utilized. If both reference and tide gauge stations need to be newly built, they can be considered for combined construction. If new stations are built, a simplified configuration can be adopted, using deep-water buoys deployed in the still waters of the port area to obtain real-time water level information.

[0039] The mobile station 103 is used to receive the GNSS satellite signal and the differential data sent by the reference station, calculate the centimeter-level three-dimensional coordinates with the reference station as the coordinate origin, measure the vertical offset between the installation position of the mobile station and the freeboard deck through a laser ranging module, and send the three-dimensional coordinates and the vertical offset to the data acquisition and control terminal. The multiple mobile stations are deployed at different positions on the ship's freeboard deck. The purpose of their deployment is to enable the data acquisition and control terminal to determine the center of gravity of the ship's deck through geometric relationships based on their coordinate data. The deployment positions of the multiple mobile stations satisfy the following: there are two mobile stations deployed on the same side of the ship, and there is a third mobile station deployed in the opposite area to that side, the opposite area including the other side, the bow, or the stern. After receiving differential data, the mobile station corrects its own position data accordingly, thereby achieving high positioning accuracy. The mobile station is a key piece of hardware in this invention and needs to be installed on the freeboard deck and superstructure of the target vessel. The mobile station simultaneously receives satellite signals and differential data from the base station, calculates its own centimeter-level precise coordinates in real time, and converts them into three-dimensional Cartesian coordinates with the base station as the origin. The mobile station also includes a laser ranging module to measure the distance between the mobile station and the freeboard deck during deployment. The mobile station also provides an LED display and a keypad for convenient bearing determination (port / starboard / fore and aft, center) and manual input of elevation differences. Additionally, the mobile station has internal storage for offline calculation and analysis. To facilitate deployment, the mobile station is equipped with strong magnets to adhere to the hull surface and a restraining device to enhance stability and prevent accidental falls.

[0040] The minimum number of mobile stations required for this application is 3, and the maximum is no more than 6. Fewer than 3 mobile stations will not be able to implement the three-point center of gravity (deck center of gravity) algorithm; more than 6 mobile stations will not help improve the calculation results.

[0041] The decision to limit the number of mobile stations to a maximum of six was based on the practice of manually reading draft gauges. These six stations should be positioned along the edge of the vessel. Figure 2As shown, the four mobile stations should be positioned as close as possible to the bow or stern on both sides of the vessel, with two on each side; the remaining two should be positioned at the center of the bow and stern, respectively. Figure 2 Points A1 and A2 on the port side, points B1 and B2 on the starboard side, point X (bow) and point Y (stern). The deployment principle of mobile stations is as follows: 1. The hull markings on the port and starboard sides should be placed as far away from the midships as possible and as close to the bow as possible; 2. The layout on both port and starboard sides should be as symmetrical as possible. For example, points A1 and B1 should be symmetrical along the ship's centerline (midship longitudinal section) as possible; 3. The bow (X) and stern (Y) should be positioned as far away from the center of the ship as possible from the centerline.

[0042] Due to various practical constraints, especially in cases of weak satellite signals or base station signals, the above principles may not be met, and principle 4 will be adopted: 4. Try to ensure that the midpoint of the longest side of the triangle formed by the three points is close to the center of gravity of the ship's deck.

[0043] When deploying the mobile station, press the button on the front panel to set its location as port / starboard / fore / stern. If at the fore / stern, also set whether it is on the ship's centerline. Additionally, if it cannot be deployed flush with the freeboard deck, use a laser rangefinder to measure the vertical distance between the mobile station and the deck (accurate to millimeters). The distance measurement result will be automatically recorded and can be manually confirmed. If the rangefinder cannot measure the distance, it should be manually entered.

[0044] Figure 2 In addition to showing the deployment locations, the display also demonstrates the wireless signal coverage of the base station and data acquisition and control terminal. The base station and data acquisition and control terminal can be located in any direction on the ship. Figure 2 The diagram illustrates four extreme scenarios, 1-4. Since the ship's hull and cargo often obstruct radio signals, when the base station and data acquisition terminal are in direction 1, point Y may not receive a signal; when in direction 2, points A1 and A2 may not receive a signal; when in direction 3, point X may not receive a signal; and when in direction 4, points B1 and B2 may not receive a signal. Therefore, regardless of the orientation of the base station and data acquisition terminal, at least three points can be guaranteed to receive a radio signal.

[0045] When there are more than 3 points where signals can be received, the data acquisition and control terminal will select data from 3 points for calculation according to the following principles: 1. Prioritize using points on the same side of the hull; 2. Next, select points on different sides of the hull; 3. Select points where the bow and stern are located on the centerline of the ship again.

[0046] The acquisition and control terminal 104 is used to receive the three-dimensional coordinates and vertical offset sent by each mobile station, subtract the difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset to obtain the calibration elevation of each mobile station on the deck plane, calculate the center of gravity coordinates of the freeboard deck using a three-point centroid algorithm based on the plane coordinates and calibration elevations of the three mobile stations, receive the tide data sent by the tide station, and calculate the actual height of the ship in the water based on the tide data and the known elevation information of the reference station, and calculate the real-time draft of the ship based on the elevation in the centroid coordinates, the water surface height, and the ship's draft depth.

[0047] In this invention, the elevation value refers to the z-axis coordinate. The data acquisition and control terminal is the core hardware component and should be placed within visual range of the mobile station for easy communication. Its main function is to collect all information and calculate the draft. The coordinate information from the mobile station needs to be filtered to eliminate the influence of periodic waves. The center point is calculated using a three-point centroid (deck centroid) algorithm, and the draft is calculated and displayed on the monitor based on the ship's freeboard height, water level information, and deck height difference. Data from the mobile station can also be imported offline into the data acquisition and control terminal via the input / output interface for delay calculation. The water surface height based on the reference station can be obtained using tidal data and the known elevation information of the reference station. Since both the deck centroid coordinates and the water surface height are based on the reference station, the distance from the deck centroid to the water surface can be calculated from the elevation in the centroid coordinates and the water surface height.

[0048] Specifically, this includes obtaining the height of the deck's center of gravity above the water surface based on the elevation and water level in the center of gravity coordinates; The draft of a ship is determined by subtracting the height of the deck's center of gravity from the waterline from the ship's hull depth.

[0049] This application provides a non-dynamic draft detection system for ships. The system includes a base station, a tide level station, multiple mobile stations, and a data acquisition and control terminal. The number of mobile stations is 3 to 6. The base station is fixedly installed at a land location with known precise coordinates. It receives GNSS satellite signals, calculates real-time observation coordinates based on the GNSS satellite signals, and calculates the error value between the real-time observation coordinates and the known precise coordinates. It then sends differential data including the error value to the mobile stations. The tide level station continuously monitors real-time tide level data in the sea area where the ship is located and sends the tide level data to the data acquisition and control terminal. The mobile stations receive the GNSS satellite signals and the differential data sent by the base station, calculate centimeter-level three-dimensional coordinates with the base station as the coordinate origin, and measure the vertical offset between the installation position of the mobile station and the freeboard deck using a laser ranging module. The three-dimensional coordinates and the vertical offset are then sent to the data acquisition and control terminal. The multiple mobile stations... The multiple mobile stations are deployed at different locations on the ship's freeboard deck. Their purpose is to enable the data acquisition and control terminal to determine the ship's deck center of gravity based on its coordinate data and geometric relationships. The deployment positions of the multiple mobile stations satisfy the following conditions: two mobile stations are deployed on the same side of the ship, and a third mobile station is deployed in the opposite area to that side, including the other side, the bow, or the stern. The data acquisition and control terminal is used to receive the three-dimensional coordinates and vertical offset sent by each mobile station, subtract the corresponding vertical offset from the elevation value in the three-dimensional coordinates to obtain the calibration elevation of each mobile station on the deck plane, calculate the center of gravity coordinates of the freeboard deck using a three-point center of gravity determination algorithm based on the plane coordinates and calibration elevations of the three mobile stations, receive the tide level data sent by the tide level station, and calculate the actual height of the ship in the water based on the tide level data and the known elevation information of the reference station. Based on the elevation in the center of gravity coordinates, the water level height, and the ship's draft, the real-time draft of the ship is calculated. The draft detection system described in this application enables efficient, convenient, and accurate ship draft detection.

[0050] In this invention, the draft calculation does not use additional sensors to measure trim / listen to correct for deviations. Instead, the deck center of gravity coordinates are directly calculated based on the three-point coordinates of the rover station, and then the draft is determined.

[0051] In one example, when the plurality of mobile stations include two mobile stations on the same side and one mobile station on the other side, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two calibrated mobile stations on the other side as the vertex, and the mobile station with the longest side formed with the vertex among the two calibrated mobile stations on the same side as the other vertex.

[0052] Figure 3(i) is a top view of the ship. Observing Figure 3(i), we can see that points B1 and B2 are located on the starboard side, and point A1 is located on the port side, nearly symmetrical to point B1 (not precisely symmetrical). Let the horizontal direction be the x-axis, the vertical direction the y-axis, and the direction perpendicular to the plane of the figure as the z-axis. Since the placement height of the mobile station may vary, the plane B1-B2-A1 is not necessarily parallel to the deck plane. Therefore, it is necessary to subtract the height difference between the mobile station and the deck recorded during placement from the z-coordinate values. Let the coordinates of the three points after adjustment be (xb1, yb1, zb1), (xb2, yb2, zb2), and (xa1, ya1, za1). This set of coordinate values ​​is equivalent to the coordinates of the plane B1-B2-A1 projected onto the deck plane along the z-axis. In Figure 3(ii), a1 is the projection of point A1, b1 is the projection of point B1, and b2 is the projection of point B2. Points b1, b2, and b1' form a right triangle, where b1 and b1' are symmetrical about the ship's centerline, and their coordinates are (xb1, yb1), (xb2, yb2), and (xb1', yb1').

[0053] Given (xb1, yb1) and (xb2, yb2), we need to find xb1' and yb1'. Since the ship's port and starboard sides are parallel, it's easy to deduce that xb1' = xb1 and yb1' = ya1. Therefore, the deck plane coordinates of points b1, b2, and b1' are (xb1, yb1), (xb2, yb2), and (xb1, ya1).

[0054] If we consider the geometric centroid of Figure 3(ii) as the center of gravity of the ship, then it must lie at the midpoint c of line segment b1'-b2. For a right triangle b1-b2-b1', the coordinates of the midpoint c of its hypotenuse b1'-b2 are ((xb1+xb2) / 2, (yb1+yb1') / 2). Since yb1' = ya1, the deck plane coordinates of c are ((xb1+xb2) / 2, (yb1+ya1) / 2). Since a1 and b1 are nearly symmetrical, a1 and b1' are very close. Therefore, we take za1=zb1', and the z-coordinate of point c is (zb2+zb1') / 2 = (zb2+za1) / 2.

[0055] Point c is the center of gravity of the deck, which represents the height of the deck above the horizontal plane, and the effects of trim / sing can be ignored.

[0056] In one example, when the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern on the centerline of the ship, the acquisition and control terminal is used to calculate the center-of-gravity coordinates of the freeboard deck based on the difference in calibration elevations of the two calibrated mobile stations on the same side, the calibration elevation of one of the calibrated mobile stations, the calibration elevation of the third mobile station, and the planar coordinates of the three mobile stations.

[0057] In Figure 4(i), the three selected points are B1 and B2 on the starboard side and the midpoint Y of the stern. Projecting these three points onto the freeboard deck, their coordinates are (xb1, yb1, zb1), (xb2, yb2, zb2), and (xy, yy, zy). As shown in Figure 4(ii), these correspond to points b1, b2, and y, respectively. An auxiliary line b1-b1' is drawn such that b1 and b1' are symmetrical about the ship's centerline. Another auxiliary line y-y' is drawn such that y-y' is perpendicular to b1-b1'. c is the midpoint of line segment y-y'. Since point y is the midpoint of the stern, it is easy to determine that the deck plane coordinates of c are ((xb1+xb2) / 2, yy). Its z-coordinate is (zb2+zb1') / 2, and zb1' = zb1 + 2*(zy-zb1) =2zy-zb1, so the z-coordinate of c is: (zb2+ 2zy - zb1) / 2.

[0058] In one example, when the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern off the centerline, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two mobile stations on the same side with the longest side formed with the calibrated mobile station at the bow / stern off the centerline, using the calibrated mobile station at the bow / stern off the centerline as the vertex and the mobile station at the longest side formed with the calibrated mobile station on the same side as the other vertex.

[0059] Figure 5(i) illustrates the worst-case scenario where the bow point X is not on the ship's centerline. In this case, point X must at least cross the ship's centerline and be as close to the port side as possible. For this situation, the midpoint of line segment x-b2 in Figure 5(ii) can be approximated as the ship's center of gravity. Since the ship's length is often several times its width, the closer point X is to the port side, the closer point c is to the center of gravity. The slight difference between these points has a limited impact on the draft calculation and can be largely ignored. If point X cannot cross the ship's centerline, the measurement should be considered a failure and abandoned.

[0060] The system consists of four parts and their information transmission relationships are as follows: Figure 6As shown, the base station and rover calculate their own positions and obtain time using GNSS satellite data provided by BeiDou / GPS. The fixed location of the base station is considered the origin of the entire system's coordinates, and the three-dimensional coordinates of all rover stations are calculated relative to this origin. The base station broadcasts differential data to the surrounding area in real time. After receiving the differential data, the rover stations correct their own position data based on this information, thus achieving high positioning accuracy (centimeter-level). The tide gauge station simultaneously provides water level information to the data acquisition and control terminal in parallel at regular intervals. At the same time, each rover station also reports its position information (its own coordinates and vertical offset from the deck) to the data acquisition and control terminal. After receiving all this information, the data acquisition and control terminal begins comprehensive calculations to ultimately obtain the precise draft of the measured vessel.

[0061] The basic components and information transmission relationships of the base station, tide station, rover station, and data acquisition and control terminal are as follows: Figure 7-10 As shown.

[0062] Figure 7 The diagram shows the internal structure of the base station, including a BeiDou / GPS receiver module, a differential calculation module, and wireless module 1. The differential calculation module performs differential data calculation based on the real-time observed coordinates sent by the BeiDou / GPS receiver module and the known coordinates. The base station transmits differential data to the rover station via wireless module 1; the rover station receives differential data from the base station via wireless module 1. The specific communication method used is determined by the base station, but a data transmission radio is generally used.

[0063] Figure 8 The demonstration showcases the internal structure of the mobile station, including a main control module, wireless module 1, a BeiDou / GPS receiver module, a differential coordinate transformation module, a storage module, a ranging module, a clock, input interfaces, output interfaces, and wireless module 2. The mobile station performs differential coordinate transformation based on data from wireless module 1 and the BeiDou / GPS receiver module, sending the calculated 3D coordinates to the storage module for offline calculation and analysis. The ranging module sends the vertical offset of the mobile station from the deck to the main control module. The main control module then sends location information and other data to the data acquisition and control terminal via wireless module 2. The data acquisition and control terminal uses wireless module 2 to receive data from the mobile station. Communication between the mobile station and the data acquisition and control terminal uses LoRa. LoRa is low-power and has high penetration; although its bandwidth is relatively low, this has no impact on the system.

[0064] Figure 9 The demonstration shows the internal structure of a tide gauge station, including a water level information acquisition module, a clock, a tide information processing module, and wireless module 3. If the tide gauge station is newly built, it can communicate with the data acquisition and control terminal via LoRa through wireless module 3. In this case, wireless modules 2 and 3 can be simplified into one module. However, if the tide gauge station is not newly built, it needs to be configured according to its communication method.

[0065] Figure 10 The display shows the internal structure of the data acquisition and control terminal, including wireless module 2, wireless module 3, filtering, draft calculation, input interface and display. The data acquisition and control terminal uses wireless module 2 to receive data sent by the mobile station and filters it to eliminate the influence of periodic waves. Based on the data from wireless modules 2 and 3, it calculates the draft and displays the results on the display.

[0066] Figure 11 h0 is the height difference between the depth datum and the tide level, and its value is provided by the tide level station (known); h1 is the height difference between the deck center of gravity and the depth datum (which can be obtained by the system of the present invention mentioned above); the ship's draft is D (known), and what needs to be calculated is the draft t.

[0067] pass Figure 11 It is easy to see that t = D - (h1 - h0), so the draft can be calculated. Here, the deck center of gravity and tide level are calculated based on the depth datum. Therefore, the height of the deck center of gravity above the water surface can be calculated by (h1 - h0). The ship's draft is obtained by subtracting the height of the ship above the water surface from the ship's molded depth.

[0068] This invention utilizes high-precision differential positioning technology based on the Global Navigation Satellite System (GNSS) to achieve high-precision determination and near real-time monitoring of the non-dynamic draft of ships in port areas. The hardware consists of four parts: a base station, a tide gauge station, a rover station, and a data acquisition and control terminal. The base station and tide gauge station can utilize existing port equipment; the rover station and data acquisition and control terminal are the main equipment of this invention. The rover station consists of 3-6 portable devices containing satellite positioning information. The rover station is deployed on the target ship by surveyors. After receiving satellite positioning information and differential information from the base station, it performs correction calculations and coordinate transformations, and then transmits the precise coordinate information to the data acquisition and control terminal via a wireless network. The data acquisition and control terminal is a modified portable laptop computer used to receive positioning information from the rover station and tide gauge information from the tide gauge station. It uses software to filter the data, determine the center point, and finally calculate the ship's draft by combining the elevation difference and water level information.

[0069] The beneficial effects of this invention include: First, this invention provides an objective and efficient method for measuring ship draft. Compared to traditional manual draft measurement methods, this invention can significantly save measurement time and reduce workload.

[0070] Secondly, it provides a non-contact method for draft monitoring. The mobile station is installed on the ship's deck / superstructure, eliminating the need for underwater deployment, and avoiding risks of seawater corrosion, snagging on the ship's bottom, collision damage, and low maintenance costs.

[0071] Third, it is suitable for all weather conditions and is less affected by weather and sea conditions.

[0072] Fourth, the positioning data can be transmitted to the shore-based monitoring center through the data acquisition and control terminal, enabling remote monitoring of the ship's draft and meeting the remote verification needs of ports and maritime authorities.

[0073] Fifth, it can achieve continuous near real-time (second-level) draft monitoring. The data acquisition and control terminal can not only calculate the draft, but also further calculate the roll or pitch angle, which is of great significance for the safety of the ship (load).

[0074] Sixth, it can be adapted to any type of ship (especially small and medium-sized vessels) without requiring any upgrades or modifications to the vessel.

[0075] Seventh, both mobile stations and data acquisition and control terminals are portable devices, which are flexible in deployment and easy to control.

[0076] The draft monitoring system provided in this application enables ports and ship owners to achieve efficient, convenient, and accurate ship draft monitoring without adding any operational complexity, thereby effectively improving production efficiency and safety levels.

[0077] Secondly, embodiments of this application provide a non-dynamic draft detection method for ships, the method comprising: The system receives GNSS satellite signals from a base station fixed at a land location with known precise coordinates, calculates real-time observation coordinates based on the GNSS satellite signals, and calculates the error value between the real-time observation coordinates and the known precise coordinates; then it sends differential data including the error value to the mobile station. The real-time tide level data of the sea area where the ship is located is continuously monitored by the tide level station, and the tide level data is sent to the acquisition and control terminal. The mobile station receives GNSS satellite signals and differential data transmitted by the base station, and calculates centimeter-level three-dimensional coordinates with the base station as the coordinate origin. A laser ranging module measures the vertical offset between the mobile station's installation position and the freeboard deck, and the three-dimensional coordinates and the vertical offset are transmitted to the data acquisition and control terminal. Multiple mobile stations are deployed at different locations on the ship's freeboard deck. Their deployment aims to enable the data acquisition and control terminal to determine the ship's deck center of gravity based on its coordinate data and geometric relationships. The deployment positions of the multiple mobile stations satisfy the following conditions: two mobile stations are deployed on the same side of the ship, and a third mobile station is deployed in the opposite area, including the other side, the bow, or the stern. The number of mobile stations is 3 to 6. The acquisition and control terminal receives the three-dimensional coordinates and vertical offset sent by each mobile station. The difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset is subtracted to obtain the calibration elevation of each mobile station on the deck plane. Based on the plane coordinates and calibration elevation of the three mobile stations, the centroid coordinates of the freeboard deck are calculated using the three-point centroid algorithm. The tidal data sent by the tidal station is received, and the actual height of the ship in the water is calculated based on the tidal data and the known elevation information of the reference station. Based on the elevation in the centroid coordinates, the water surface height, and the ship's draft, the real-time draft of the ship is calculated.

[0078] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station on the other side, the step of calculating the center-of-gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station on the other side as the vertex, the mobile station with the longest side formed with the calibrated mobile station on the same side is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

[0079] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern along the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated rover station at the bow / stern of the ship's centerline as the vertex, and the rover station with the longest side formed with the calibrated rover station on the same side as the other vertex, the coordinates of the center of gravity of the freeboard deck are calculated based on the difference in calibration elevations of the two vertices, the calibration elevation of one of the vertices, the calibration elevation of the third rover station, and the planar coordinates of the three rover stations.

[0080] In one possible implementation, when the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern not on the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station at the bow / stern (not on the centerline) as the vertex, the mobile station with the longest side formed by the two calibrated mobile stations on the same side as the calibrated mobile station is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

[0081] Thirdly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any of the above-described methods for non-dynamic draft detection of ships.

[0082] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid state disk (SSD)).

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0084] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the method embodiments are described more simply because they are similar to the system embodiments; relevant parts can be referred to the descriptions of the system embodiments.

[0085] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A non-dynamic draft detection system for ships, characterized in that, The system includes a base station, a tide gauge station, multiple rover stations, and a data acquisition and control terminal, wherein the number of rover stations is 3 to 6. The base station is fixedly set at a land location with known precise coordinates to receive GNSS satellite signals, calculate the real-time observation coordinates based on the GNSS satellite signals, and calculate the error value between the real-time observation coordinates and the known precise coordinates. Send differential data including the error value to the mobile station; The tide level station is used to continuously monitor the real-time tide level data of the sea area where the ship is located and send the tide level data to the acquisition and control terminal. The mobile station is used to receive GNSS satellite signals and differential data sent by the reference station, calculate centimeter-level three-dimensional coordinates with the reference station as the origin, measure the vertical offset between the installation position of the mobile station and the freeboard deck using a laser ranging module, and send the three-dimensional coordinates and the vertical offset to the data acquisition and control terminal. The multiple mobile stations are deployed at different positions on the ship's freeboard deck, and their deployment purpose is to enable the data acquisition and control terminal to determine the center of gravity of the ship's deck through geometric relationships based on their coordinate data. The deployment positions of the multiple mobile stations satisfy the following: there are two mobile stations deployed on the same side of the ship, and there is a third mobile station deployed in the opposite area to that side, the opposite area including the other side, the bow, or the stern. The acquisition and control terminal is used to receive the three-dimensional coordinates and vertical offset sent by each mobile station, subtract the difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset to obtain the calibration elevation of each mobile station on the deck plane, calculate the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the plane coordinates and calibration elevations of the three mobile stations, receive the tide level data sent by the tide level station, and calculate the actual height of the ship in the water based on the tide level data and the known elevation information of the reference station, and calculate the real-time draft of the ship based on the elevation in the centroid coordinates, the water level height, and the ship's draft depth.

2. The system according to claim 1, characterized in that, When the plurality of mobile stations include two mobile stations on the same side and one mobile station on the other side, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two calibrated mobile stations on the other side as the vertex, and the mobile station with the longest side formed with the vertex among the two calibrated mobile stations on the same side as the other vertex.

3. The system according to claim 1, characterized in that, When the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern on the centerline of the ship, the acquisition and control terminal is used to calculate the center-of-gravity coordinates of the freeboard deck based on the difference in calibration elevations of the two calibrated mobile stations at the bow / stern on the centerline of the ship as the vertex, the mobile station with the longest side formed with the first vertex among the two calibrated mobile stations on the same side as the second vertex, the calibration elevation of one of the calibrated vertices, the calibration elevation of the third mobile station, and the planar coordinates of the three mobile stations.

4. The system according to claim 1, characterized in that, When the plurality of mobile stations include two mobile stations on the same side and one mobile station at the bow / stern off the centerline, the acquisition and control terminal is used to calculate the center of gravity coordinates of the freeboard deck based on the plane coordinates of the two mobile stations on the same side after calibration, taking the calibrated mobile station at the bow / stern off the centerline as the vertex and the mobile station with the longest side formed with the calibrated mobile station at the same side as the other vertex.

5. The system according to claim 1, characterized in that, The calculation of the ship's real-time draft based on the elevation, water level, and ship depth in the centroid coordinate system includes: The height of the deck's center of gravity above the water surface is obtained from the elevation and water level in the center of gravity coordinates. The draft of a ship is determined by subtracting the height of the deck's center of gravity from the waterline from the ship's hull depth.

6. A method for non-dynamic draft detection of a ship, characterized in that, The method includes: The system receives GNSS satellite signals from a base station fixed at a land location with known precise coordinates, calculates real-time observation coordinates based on the GNSS satellite signals, and calculates the error value between the real-time observation coordinates and the known precise coordinates; then it sends differential data including the error value to the mobile station. The real-time tide level data of the sea area where the ship is located is continuously monitored by the tide level station, and the tide level data is sent to the acquisition and control terminal. The mobile station receives GNSS satellite signals and differential data transmitted by the base station, and calculates centimeter-level three-dimensional coordinates with the base station as the coordinate origin. A laser ranging module measures the vertical offset between the mobile station's installation position and the freeboard deck, and the three-dimensional coordinates and the vertical offset are transmitted to the data acquisition and control terminal. Multiple mobile stations are deployed at different locations on the ship's freeboard deck. Their deployment aims to enable the data acquisition and control terminal to determine the ship's deck center of gravity based on its coordinate data and geometric relationships. The deployment positions of the multiple mobile stations satisfy the following conditions: two mobile stations are deployed on the same side of the ship, and a third mobile station is deployed in the opposite area, including the other side, the bow, or the stern. The number of mobile stations is 3 to 6. The acquisition and control terminal receives the three-dimensional coordinates and vertical offset sent by each mobile station. The difference between the elevation value in the three-dimensional coordinates and the corresponding vertical offset is subtracted to obtain the calibration elevation of each mobile station on the deck plane. Based on the plane coordinates and calibration elevation of the three mobile stations, the centroid coordinates of the freeboard deck are calculated using the three-point centroid algorithm. The tidal data sent by the tidal station is received, and the actual height of the ship in the water is calculated based on the tidal data and the known elevation information of the reference station. Based on the elevation in the centroid coordinates, the water surface height, and the ship's draft, the real-time draft of the ship is calculated.

7. The method according to claim 6, characterized in that, When the plurality of mobile stations includes two mobile stations on the same side and one mobile station on the other side, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station on the other side as the vertex, the mobile station with the longest side formed with the calibrated mobile station on the same side is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

8. The method according to claim 6, characterized in that, When the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern along the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated rover station at the bow / stern of the ship's centerline as the vertex, and the rover station with the longest side formed with the calibrated rover station on the same side as the other vertex, the coordinates of the center of gravity of the freeboard deck are calculated based on the difference in calibration elevations of the two vertices, the calibration elevation of one of the vertices, the calibration elevation of the third rover station, and the planar coordinates of the three rover stations.

9. The method according to claim 6, characterized in that, When the plurality of mobile stations includes two mobile stations on the same side and one mobile station at the bow / stern not on the centerline, the calculation of the center of gravity coordinates of the freeboard deck using a three-point centroid determination algorithm based on the planar coordinates and calibration elevation of the three mobile stations includes: Using the calibrated mobile station at the bow / stern (not on the centerline) as the vertex, the mobile station with the longest side formed with this vertex among the two calibrated mobile stations on the same side is taken as the other vertex. The coordinates of the center of gravity of the freeboard deck are calculated based on the planar coordinates of the two vertices and the calibration elevation.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 6-9.

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