Anchoring method for a marine autonomous surface vessel
By employing a mooring method based on real-time data acquisition and autonomous decision-making, the problems of insufficient environmental change and ship dynamic response in traditional mooring methods have been solved, thereby improving the safety and stability of autonomous ship mooring.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DALIAN MARITIME UNIVERSITY
- Filing Date
- 2026-04-15
- Publication Date
- 2026-06-05
AI Technical Summary
Traditional anchoring methods rely on human experience and are difficult to respond to environmental changes and ship dynamics in real time, making the anchoring process of autonomous vessels complex and fraught with safety risks.
It collects real-time data on ship status, environment, and anchoring equipment, autonomously generates anchoring plans, and issues alarms and re-decision when safety conditions are not met, continuously monitoring the anchoring status to trigger automatic responses.
It improves the pertinence and timeliness of anchoring decisions, reduces safety risks, and enhances the stability and safety of autonomous vessels anchoring.
Smart Images
Figure CN122144093A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ship anchoring technology, and in particular to an anchoring method for autonomous surface vessels at sea. Background Technology
[0002] Anchoring is a fundamental and crucial operation in maritime navigation, typically requiring crew members to manually make a series of decisions and take actions based on on-site environmental conditions, the ship's condition, and the performance of the anchoring equipment. However, traditional anchoring processes rely on human experience and manual adjustments, making them susceptible to crew misjudgments, environmental changes, and other factors, thus increasing navigational risks and operational difficulty.
[0003] With the continuous development of autonomous surface vessel (MASS) technology, the demand for autonomous vessels is increasing. Against this backdrop, traditional anchoring methods face challenges. Anchoring operations for autonomous vessels not only require consideration of automated vessel control but also must cope with complex and dynamically changing marine environments (such as wind, waves, currents, and tides). These factors make the process of finding and anchoring a vessel more complex and uncertain, thus making reliance on manual operation and traditional methods particularly unsuitable.
[0004] Existing anchoring systems largely rely on fixed parameters preset by crew members and traditional manual adjustments, lacking real-time intelligent analysis of ship status, environmental changes, and anchoring equipment status. This makes it difficult to establish a coordinated decision-making mechanism around anchor selection, anchoring timing, anchoring speed, and chain length. These systems cannot respond promptly to environmental changes and ship dynamics, potentially leading to risks such as dragging anchor, anchor tethering, and equipment malfunctions during anchoring, and in severe cases, even collisions and grounding.
[0005] Therefore, there is an urgent need for an anchoring method for autonomous surface vessels that combines safety, stability, and efficiency in ship anchoring operations. Summary of the Invention
[0006] In view of this, the present invention provides an anchoring method for autonomous surface vessels at sea, which collects real-time vessel status data, environmental data, and anchoring equipment status data; performs calculations and analysis based on the collected data to generate autonomous anchoring decision results; issues alarm information when the decision results do not meet preset safety conditions, and re-decides decisions after the response measures are ineffective; continuously monitors the anchoring status after the vessel has anchored, and triggers automatic response or dragging anchor alarm when an anomaly is detected; thus realizing autonomous anchoring of the vessel.
[0007] Therefore, the present invention provides the following technical solution:
[0008] An anchoring method for autonomous surface vessels at sea, comprising: Real-time collection of ship status data, environmental data, and anchoring equipment status data; Based on ship status data, environmental data, and anchoring equipment status data, autonomous anchoring decisions are made, and the results of the decisions, such as target anchor position, anchoring timing, anchoring speed, and chain length, are output. If any decision result does not meet the preset safety conditions, an alarm message will be output, and a re-collection and re-decision will be triggered; After the vessel has anchored, its anchoring status is continuously monitored. If any abnormality occurs, an automatic response or dragging anchor alarm will be triggered.
[0009] Furthermore, the autonomous anchoring decision-making includes: If multiple anchoring feasibility assessments are passed simultaneously, the candidate anchorage will be used as the target anchorage; if any one of them fails, a new candidate anchorage will be selected. After determining the target anchor position, the timing of anchoring is determined based on the direction of environmental forces and the ship's residual kinetic energy: Based on the direction of environmental forces, position the ship in a favorable orientation against the wind or current; When the residual kinetic energy is less than the threshold allowed by the anchor winch braking system and the anchor holding force, the anchoring speed is determined according to the safety constraint of the anchor chain tension. If the residual kinetic energy is greater than or equal to the threshold allowed by the anchor winch braking system and anchor holding force, then decelerate and wait; After determining the anchoring speed, anchoring is carried out, and the compensation length is calculated based on the total environmental load to determine the chain extension length.
[0010] Furthermore, the anchoring feasibility assessment includes: Water depth safety assessment, seabed grip assessment, and safe turning range verification; The water depth safety assessment: If the actual water depth of the candidate anchorage meets the safety range, the water depth safety assessment is passed; the safety range of the actual water depth of the candidate anchorage:
[0011] in, For the ship's draft, Because of the abundance of deep water, The maximum water depth at which anchoring can be carried out, determined in conjunction with the capabilities of the anchoring equipment; This refers to the actual water depth. The seabed holding capacity assessment is as follows: if the total anchoring force is greater than or equal to the total environmental load, the seabed holding capacity assessment is passed. The safe turning range verification is as follows: the minimum distance from the candidate anchorage to surrounding obstructions, channel boundaries and adjacent vessels must be greater than or equal to the sum of the safe turning radius and the preset safe distance, then the safe turning range verification is passed.
[0012] Furthermore, the ship's residual kinetic energy includes:
[0013] in, As residual kinetic energy, For ship quality, For added mass, For ground speed.
[0014] Furthermore, determining the anchoring speed based on the safety constraint of the anchor chain tension includes: The anchor chain tension is determined by constructing an equation based on the dissipation of the ship's residual kinetic energy at the moment of anchoring by the work done by the ship's wind resistance, water resistance and anchor chain tension after the anchor touches the bottom. The range of anchoring speed is determined by solving the equation with the anchor holding force corresponding to the bottom conditions of the target anchoring position as the lower limit of the anchor chain tension and the allowable braking force of the anchor winch braking system as the upper limit of the anchor chain tension. The equation:
[0015] in, For the wind resistance of the hull, For the water resistance of the hull, For anchor chain tension, This refers to the horizontal displacement from the moment the anchor touches the bottom until the ship comes to a stop. This refers to the horizontal displacement from the moment the anchor touches the bottom until it firmly grips the ground. For ship quality, For added mass, This is the ship's speed relative to the ground when anchored.
[0016] Furthermore, the step of determining the chain length based on the compensation length calculated according to the total environmental load includes: The outgoing chain length is the sum of the base outgoing chain length and the compensation length; The range of the basic chain extension length is 4-8 times the water depth of the target anchorage, and is selected within this range based on experience. The compensation length is calculated based on the total environmental load.
[0017] in, For compensation coefficient, The total environmental load formed by the combined effects of wind, current, and waves. The total resistance that the mooring system can provide under the target anchorage conditions; To compensate for the length.
[0018] Furthermore, the abnormal state includes: Abnormal position drift, abnormal anchor chain tension, or abnormal movement posture.
[0019] Further, the automatic response includes: Completing the chain, increasing the ship's draft or dropping a second anchor.
[0020] Further, the ship status data includes: ship position, course, speed, draft and ship attitude; Environmental data includes: wind speed, wind direction, flow velocity, flow direction, wave height, water depth, seabed information, forecast wind, forecast flow and forecast wave parameters; Anchoring equipment status data includes: anchor status and anchor chain tension.
[0021] An anchoring system for an autonomous surface ship at sea, comprising: An information acquisition module, an information processing and decision-making module, an alarm module and a monitoring module; The information acquisition module acquires ship status data, environmental data and anchoring equipment status data in real time; The information processing and decision-making module makes an autonomous decision on anchoring based on the ship status data, environmental data and anchoring equipment status data, and outputs decision results on anchor position selection, anchoring time, anchoring speed and chain length; The alarm module outputs an alarm message when any decision result does not meet the preset safety conditions, and triggers re-acquisition and re-decision; The monitoring module continuously monitors the anchoring status after the ship has dropped the anchor. If an abnormal status occurs, it triggers an automatic response or a dragging anchor alarm.
[0022] Advantages and positive effects of the present invention: The present invention can perform real-time linkage analysis based on the ship status, environmental changes and anchoring equipment status, and form autonomous decision results on anchor position selection, anchoring time, anchoring speed and chain length, thereby improving the pertinence and timeliness of the anchoring decision. The present invention constructs a closed-loop mechanism of "decision - alarm - data update - re-decision", which can adjust the anchoring plan in time when the decision result does not meet the preset safety conditions, and improve the adaptability in complex sea conditions. By continuously analyzing the changes in ship position, anchor chain tension and ship motion attitude, the present invention can timely identify the risk of dragging anchor, and trigger an automatic response or a dragging anchor alarm in case of an abnormality, thereby improving the safety and stability during anchoring. Description of the Drawings
[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.
[0024] Figure 1 This is a structural block diagram of the anchoring system for autonomous surface vessels in Example 2; Figure 2 This is an example diagram of the anchoring system structure for autonomous surface vessels in Example 2; Figure 3 This is a flowchart of the anchoring method for autonomous surface vessels at sea in Example 1; Figure 4 This is a schematic diagram of the workflow of the information processing and decision-making module in Example 2; Figure 5 This is a flowchart of the anchor drag analysis in Example 1; Figure 6 This is a flowchart of the anchor preparation, anchor placement, and anchor sinking process in Example 1. Detailed Implementation
[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.
[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.
[0027] This invention provides an anchoring method for autonomous surface vessels at sea. It involves real-time collection of vessel status data, environmental data, and anchoring equipment status data to determine the target anchor position, anchoring timing, anchoring speed, and chain extension length. If any decision result for the target anchor position, anchoring timing, anchoring speed, or chain extension length fails to meet preset safety conditions, an alarm module outputs an alarm message. After the response measures prove ineffective, the system re-collects vessel status data, environmental data, and anchoring equipment status data and re-determines the target anchor position, anchoring timing, anchoring speed, and chain extension length.
[0028] Example 1 like Figure 3 As shown, an anchoring method for autonomous surface vessels at sea includes the following steps: S1. Information Collection: Real-time collection of ship status data, environmental data, and anchoring equipment status data; S2, such as Figure 4 As shown, information processing and decision-making: The target anchor position, the timing of anchoring, the anchoring speed, and the length of the chain are determined.
[0029] 1) When multiple anchoring feasibility assessments are passed simultaneously, the candidate anchorage will be used as the target anchorage.
[0030] If a candidate anchorage simultaneously meets the requirements of water depth suitability, bottom gripping suitability, and safe turning range, then the candidate anchorage will be used as the target anchorage.
[0031] Water depth safety assessment includes: whether the actual water depth of the candidate anchorage meets the preset depth range, expressed by the formula:
[0032] in, For the ship's draft, Because of the abundance of deep water, The maximum water depth at which anchoring can be carried out, determined in conjunction with the capabilities of the anchoring equipment; This represents the actual water depth.
[0033] Seabed gripping strength assessment: If the total anchoring force is greater than or equal to the total environmental load, the seabed gripping strength requirement is met. The total environmental load can be characterized as:
[0034] in, Total environmental load; , , These are the equivalent environmental loads of wind, current, and waves acting on the ship, respectively.
[0035] Total anchoring force:
[0036]
[0037]
[0038] in, For anchor holding force; For the friction of the underfloor anchor chain; To determine the bottom-holding coefficient under corresponding anchor type and bottom conditions, The force of gravity when anchored in the air; The coefficient of friction between the anchor chain and the seabed. This refers to the weight per unit length of the anchor chain. This refers to the length of the bottom-holding chain segment. Seabed information is obtained through electronic charts, geological survey data, or real-time detection results, and a preset seabed gripping coefficient table is invoked based on the actual anchor type equipped on the vessel.
[0039] Safety range determination: The minimum distance from the candidate anchorage to surrounding obstructions, channel boundaries, and adjacent vessels must be greater than or equal to the sum of the safe turning radius and the preset safe distance, expressed by the formula:
[0040]
[0041] in, The minimum distance from the candidate anchorage to surrounding obstructions, channel boundaries, and adjacent vessels. Preset safety distance; For a safe turning radius, To achieve the planned target chain length, As captain, This is the correction amount for the cyclone caused by wind, current, and waves.
[0042] 2. After determining the target anchor position, determine the timing for anchoring.
[0043] Continuously monitor the direction of the combined environmental forces formed by wind, current, and waves, and guide ships to favorable positions against the wind and current based on the direction of the combined environmental forces.
[0044] Check if the residual kinetic energy is less than the threshold allowed by the anchor winch braking system and anchor holding force. If it is less, proceed to the next step of confirming the anchoring speed. If it is greater, continue to decelerate and wait.
[0045] The formula for calculating the residual kinetic energy of a ship is:
[0046] in, As residual kinetic energy, For ship quality, For added mass, For ground speed.
[0047] 3) Determine the anchoring speed after determining the timing for anchoring.
[0048] The critical values of the anchoring speed range are respectively based on the anchor holding force corresponding to the bottom conditions at the target anchorage. The anchor winch braking system allows braking force It is used as a constraint condition for solving.
[0049] when The anchoring speed obtained at that time The range is the recommended anchoring speed range.
[0050] The residual kinetic energy of a ship at the moment of anchoring is dissipated by the work done by the ship's wind resistance, water resistance, and anchor chain tension after the anchor touches the bottom. The formula is as follows:
[0051] in, For the wind resistance of the hull, For the water resistance of the hull, For anchor chain tension, This refers to the horizontal displacement from the moment the anchor touches the bottom until the ship comes to a stop. This refers to the horizontal displacement from the moment the anchor touches the bottom until it firmly grips the ground. For ship quality, For added mass, This is the ship's speed relative to the ground when anchored.
[0052] The formula for water resistance is:
[0053]
[0054]
[0055]
[0056] in, For the ship's speed relative to the water, For the density of water, As captain, For the width of the boat, For drinking water, The square coefficient, For coefficients, The viscosity coefficient of water movement.
[0057] 4) Determine the chain length; Outgoing chain length includes: basic outgoing chain length and compensation length.
[0058] The basic chain length is equal to 4-6 times the water depth under normal sea conditions, and 6-8 times the water depth under severe sea conditions; The formula for compensation length is:
[0059] in, For compensation coefficient, The total environmental load formed by the combined effects of wind, current, and waves. The total resistance that the mooring system can provide under the target anchorage conditions.
[0060] S3, Alarm and Re-decision.
[0061] When any decision result among the target anchor position, anchoring timing, anchoring speed, or chain length does not meet the preset safety conditions, the alarm module outputs an alarm message, and after the response measures are ineffective, it re-enters S1, collects the ship status data, environmental data, and anchoring equipment status data, and executes S2 again.
[0062] S4. Continuous monitoring and automatic response.
[0063] like Figure 5 As shown, after the vessel anchors, the system continuously acquires the vessel's position, heading, anchor chain tension, and environmental parameters, and establishes an electronic safety fence based on the anchoring location. Then, it continuously performs position drift analysis, anchor chain tension analysis, and motion attitude analysis. Anomaly flags from these three analyses are summarized. If any anomaly flag is 1, a response measure is triggered. If all anomaly flags are 0, the status is normal, and routine monitoring continues. When the monitoring module detects an anomaly, the system first executes automatic response measures.
[0064] An abnormal position drift is defined as: the vessel's position exceeds the fence, which is a circular area centered on the anchorage and with a radius equal to the minimum distance from the candidate anchorage to surrounding obstructions, channel boundaries, and adjacent vessels. Anomaly in anchor chain tension is caused by the resultant force of the environment exceeding the anchor chain tension. An abnormal motion attitude is defined as: the ship's motion trajectory is directional drifting and the rate of change of heading is less than 5° / minute.
[0065] Automatic response measures include chain replenishment, increasing the ship's draft, and dropping a second anchor. If the automatic response fails, the system issues an anchor dragging alarm and, after raising the anchor, re-enters step S1. Based on the latest collected data, it re-determines the target anchor position, anchoring timing, anchoring speed, and chain length, thus forming a closed-loop anchoring control process of "information collection—information processing and decision-making—alarm and re-decision-making—continuous monitoring and automatic response".
[0066] In this embodiment, the anchor preparation, anchor placement, and anchor sinking process is as follows: Figure 6 As shown: 1. Confirm the final anchor position; 2. Power on the anchor winch, brake firmly, disengage the clutch, and close the chain stopper; 3. Remove the baffle plate and the cover plate at the top of the anchor chain tube; 4. Engage the clutch, start the anchor winch, and open the chain stopper; 5. Release the brake, start the anchor winch to send the anchor to the ready position; 6. Brake firmly, disengage the clutch, and wait for anchoring; 7. Upon receiving the anchoring command, release the brake and anchor; 8. Anchor on the bottom; 9. Proceed to the subsequent anchor chain length and bottom grip confirmation process.
[0067] Example 2 like Figure 1 and Figure 2 As shown, this embodiment provides an intelligent anchoring system for autonomous surface vessels at sea, including: The system includes an information acquisition module, an information processing and decision-making module, an alarm module, and a monitoring module.
[0068] 1. The information acquisition module is used to collect real-time ship status data, environmental data, and anchoring equipment status data.
[0069] 1) Ship status data, including: position, heading, speed, draft, and attitude; 2) Environmental data, including: wind speed, wind direction, current speed, current direction, wave height, water depth, seabed information, forecast wind, forecast current, and forecast wave parameters; 3) Anchoring equipment status data, including: anchor status and anchor chain tension.
[0070] 2. The information processing and decision-making module is used to make autonomous anchoring decisions based on ship status data, environmental data, and anchoring equipment status data, and output the decision results of anchor position selection, anchoring timing, anchoring speed, and chain length.
[0071] 3. The alarm module is used to output alarm information and trigger re-collection and re-decision when any decision result does not meet the preset safety conditions.
[0072] 4. The monitoring module is used to continuously monitor the anchoring status after the vessel has finished anchoring, and to trigger an automatic response or dragging anchor alarm when an anomaly is detected.
[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for anchoring autonomous surface vessels at sea, characterized in that, include: Real-time collection of ship status data, environmental data, and anchoring equipment status data; Based on ship status data, environmental data, and anchoring equipment status data, autonomous anchoring decisions are made, and the results of the decisions, such as target anchor position, anchoring timing, anchoring speed, and chain length, are output. If any decision result does not meet the preset safety conditions, an alarm message will be output, and a re-collection and re-decision will be triggered; After the vessel has anchored, its anchoring status is continuously monitored. If any abnormality occurs, an automatic response or dragging anchor alarm will be triggered.
2. The method according to claim 1, characterized in that, The autonomous anchoring decision-making includes: If multiple anchoring feasibility assessments are passed simultaneously, the candidate anchorage will be used as the target anchorage; if any one of them fails, a new candidate anchorage will be selected. After determining the target anchor position, the timing of anchoring is determined based on the direction of environmental forces and the ship's residual kinetic energy: Based on the direction of environmental forces, position the ship in a favorable orientation against the wind or current; When the residual kinetic energy is less than the threshold allowed by the anchor winch braking system and the anchor holding force, the anchoring speed is determined according to the safety constraint of the anchor chain tension. If the residual kinetic energy is greater than or equal to the threshold allowed by the anchor winch braking system and anchor holding force, then decelerate and wait; After determining the anchoring speed, anchoring is carried out, and the compensation length is calculated based on the total environmental load to determine the chain extension length.
3. The method according to claim 2, characterized in that, The anchoring feasibility assessment includes: Water depth safety assessment, seabed grip assessment, and safe turning range verification; The water depth safety assessment: If the actual water depth of the candidate anchorage meets the safety range, the water depth safety assessment is passed; the safety range of the actual water depth of the candidate anchorage: in, For the ship's draft, Because of the abundance of deep water, The maximum water depth at which anchoring can be carried out, determined in conjunction with the capabilities of the anchoring equipment; This refers to the actual water depth. The seabed holding capacity assessment is as follows: if the total anchoring force is greater than or equal to the total environmental load, the seabed holding capacity assessment is passed. The safe turning range verification is as follows: the minimum distance from the candidate anchorage to surrounding obstructions, channel boundaries and adjacent vessels must be greater than or equal to the sum of the safe turning radius and the preset safe distance, then the safe turning range verification is passed.
4. The method according to claim 2, characterized in that, The ship's residual kinetic energy includes: in, As residual kinetic energy, For ship quality, For added mass, For ground speed.
5. The method according to claim 2, characterized in that, The determination of anchoring speed based on the safety constraint of anchor chain tension includes: The anchor chain tension is determined by constructing an equation based on the dissipation of the ship's residual kinetic energy at the moment of anchoring by the work done by the ship's wind resistance, water resistance and anchor chain tension after the anchor touches the bottom. The range of anchoring speed is determined by solving the equation with the anchor holding force corresponding to the bottom conditions of the target anchoring position as the lower limit of the anchor chain tension and the allowable braking force of the anchor winch braking system as the upper limit of the anchor chain tension. The equation: in, For the wind resistance of the hull, For the water resistance of the hull, For anchor chain tension, This refers to the horizontal displacement from the moment the anchor touches the bottom until the ship comes to a stop. This refers to the horizontal displacement from the moment the anchor touches the bottom until it firmly grips the ground. For ship quality, For added mass, This is the ship's speed relative to the ground when anchored.
6. The method according to claim 2, characterized in that, The process of determining the chain length based on the compensation length calculated according to the total environmental load includes: The outgoing chain length is the sum of the base outgoing chain length and the compensation length; The range of the basic chain extension length is 4-8 times the water depth of the target anchorage, and is selected within this range based on experience. The compensation length is calculated based on the total environmental load. in, For compensation coefficient, The total environmental load formed by the combined effects of wind, current, and waves. The total resistance that the mooring system can provide under the target anchorage conditions; To compensate for the length.
7. The method according to claim 1, characterized in that, The abnormal states include: Abnormal position drift, abnormal anchor chain tension, or abnormal movement posture.
8. The method according to claim 1, characterized in that, The automatic response includes: Repair the chain, increase the ship's draft, or drop a second anchor.
9. The method according to claim 1, characterized in that, The ship status data includes: ship position, heading, speed, draft, and ship attitude; Environmental data, including: wind speed, wind direction, current speed, current direction, wave height, water depth, seabed information, forecast wind, forecast current, and forecast wave parameters; Anchorage equipment status data, including: anchor status and anchor chain tension.
10. An anchoring system for autonomous surface vessels at sea, characterized in that, include: Information acquisition module, information processing and decision-making module, alarm module, and monitoring module; The information acquisition module collects real-time data on ship status, environmental data, and anchoring equipment status. The information processing and decision-making module, based on ship status data, environmental data, and anchoring equipment status data, performs autonomous anchoring decisions and outputs decision results on anchor position selection, anchoring timing, anchoring speed, and chain length. The alarm module outputs an alarm message and triggers re-collection and re-decision when any decision result does not meet the preset safety conditions; The monitoring module continuously monitors the anchoring status after the vessel has anchored. If any abnormality occurs, it will trigger an automatic response or an anchor dragging alarm.