PROVISION OF THE PROBLEM OF NAVIGATION

SECURITY

5.1. ESSENCE OF THE PROBLEM OF NAVIGATION
SECURITY

The equipment of ships with gyrocompasses, electronic relative and hydroacoustic absolute logs, radio navigation systems, radar facilities, global satellite navigation systems, integrated navigation systems, vessel heading and trajectory control systems, electronic cartographic navigation and information systems caused significant changes in navigation methods, but to a qualitative leap – has not yet led to the complete transfer of managerial functions to the machine. This is explained by the fact that, in accordance with the dialectic of development, the methods of navigation and the principles of organizing navigation service on ships objectively lag behind the development of technical means of navigation and control. Modern navigation – a fusion of science and the art of management – remains a human activity in conditions of increased danger. The complication of the activity of a modern navigator is associated with the development of a network of ports and sea routes, an increase in the total number of ships, their displacement, size and speed, and an increase in the density of traffic flows.

Ensuring navigational safety is a necessary condition for protecting life at sea and the environment from pollution. Navigational errors and misses in the management of ships still lead to human casualties, material damage and environmental disasters. In 1960-1979. about 300 ships were lost at sea every year, which is 0.4% of the total number of ships in the world fleet. At present, this figure has somewhat decreased. At the same time, navigation accidents account for about 50% of all accidents. An alternative to navigational accidents is navigational safety, i.e. such a state of the ship in specific circumstances, when the minimum risk of the ship running aground, touching the ground, colliding with an artificial or natural obstacle, leaving the ship as a result of navigational errors outside the established zone or water area is ensured.

Numerous scientific studies, technical developments and organizational measures are aimed at improving this safety. However, a quantitative assessment of the achieved level of navigational safety and the impact of ongoing activities on it causes serious difficulties. Accident statistics reflect only long-term trends in the past, which reduces their importance for prompt action. Therefore, along with the statistical analysis of the accident rate, it is apparently necessary to develop methods for quantifying the influence of individual factors on navigational safety.

Navigational hazards are natural and artificial objects located on the surface and in the depths of the oceans, which pose a real threat to the ship. Natural hazards include: coastline, shoals, shoals, banks, reefs, rocks, etc. Artificial structures include: hydraulic structures, soil dumps, rigs, drilling and fishing towers, platforms, supports and high-voltage transmission lines, mine and side barriers, anti-submarine and fishing nets, etc.

For low-tonnage and small size vessels; including those with dynamic support means and a waterline of a limited area, the real danger is represented by floating fencing signs, anchor barrels, logs, tree roots, etc. For such vessels, the main problem of ensuring navigation safety is the lack of reliable means and methods for detecting the listed hazards at night and in conditions of limited visibility. Therefore, the operation of these vessels under these conditions is prohibited.

Fixed navigational hazards are shown on navigation charts, information about them is contained in sailing directions and navigation manuals. Information about new objects in the sea that pose a threat to navigation is contained in the sources of operational information on the navigation situation (IM, NAVIM, NAVIP, NAVAREA, etc.).

Skippers have developed a certain professional stereotype: the more accurate the ship’s coordinates and the farther it is from the coastline, the lower the degree of danger. However, this rule does not apply to submersibles and submersibles, very deep draft vessels and deep sea fishing gear of fishing vessels. For vessels of these classes, navigational hazards are all elements of the seabed topography adjacent to the navigation horizon (depth of immersion or draft). Due to the increase in coordination errors in the hydrographic survey of the seabed with distance from the coastline, the danger of navigation of underwater vessels, apparatuses, vessels with a very deep draft and deep-sea fishing gear also increases. For, even with a high accuracy of knowledge on these ships of their own coordinates, their position regarding underwater dangers is aggravated by significant errors.

Navigational safety on ships is ensured by a set of measures, which include:

• professional training of navigators;

• technical serviceability of technical means of navigation and communication;

• availability of the necessary set of corrected navigational charts, manuals and manuals for navigation;

• knowledge and consideration by navigators of navigational, hydrographic and hydrometeorological conditions of navigation;

• clear organization and implementation of procedures for keeping a watch;

• strict implementation of the rules of navigation and the International Rules for Avoiding Collisions of Vessels;

• continuous monitoring of the ship’s position.

It should be added that, in addition to ensuring navigational safety, navigators are responsible for monitoring the stability and unsinkability of ships, their explosion and fire safety.

Thus, the process of maritime navigation, and especially navigation on inland waterways, is complex and dynamic, associated with a significant number of objective and subjective factors. Without knowledge of the laws governing complex systems, the transition to automated navigation, to the scientific organization of labor, is impossible. The tool for understanding the connections, analyzing and implementing these laws is the general theory of control (cybernetics), which allows you to objectively evaluate the process of modern navigation, its means, methods and organization.

5.2. MEANS AND METHODS OF OBSERVATION
AND SHIP CONTROL

Prevention of navigational incidents (accidents) at sea and on inland waterways is initially ensured by observation, and then by the control of the ship, undertaken in order to prevent collision of ships, impact, bulk, grounding.

Surveillance is a set of application of means and methods for searching, detecting and classifying environmental objects for the purpose of efficient and safe ship management. Management – making a decision to save or change the parameters of the vessel’s movement (course, speed), issuing appropriate commands, giving signals, their execution and control over their implementation.

Surveillance for the prevention of accidents with a vessel on inland waterways or collisions at sea is carried out in order to fully assess the situation in which one’s own vessel is. At the same time, the content of the observation is the collection, processing and analysis of information about external and internal factors affecting the state of the vessel and the development of the existing situation.

In all cases, the primary task of observation is to determine whether there is a risk of collision or other emergency. When the navigator has doubts about the safe development of the existing situation, it should be considered that its development leads to a collision of ships, impact, bulk, grounding or other emergency.

Visual observation is carried out by the persons of the navigation watch, as well as the pilot on board. It must be continuous, qualified and reliable.

Visual means of observation include optical direction finders, binoculars, spotting scopes, optical rangefinders and searchlights.

Through visual observation, pilotage navigation methods are implemented, based on an eye assessment of the position of the vessel relative to the navigation situation and dangers, since visual means and methods allow you to obtain information in an explicit form, directly assess the situation and make the necessary decision.

Pilot methods of navigation at the present stage are also used by technical means of observation: ship radars, AIS, ECDIS and echo sounders.

Radar surveillance includes: detection of objects, determination of their position relative to the vessel and determination of the degree of danger. Radar surveillance is indispensable in conditions of limited visibility and navigation in cramped conditions. However, information from the radar regarding moving objects appears in an implicit form, and therefore needs to be processed, i.e. in charge of radar. Radar plotting provides for: determining the elements of the movement of objects (targets) and their relative courses, determining the degree of danger and its quantitative assessment, calculating the safe divergence maneuver and monitoring its implementation. Radar plotting is carried out by means of graphical problem solving, theoretically based on the relative motion method: manually (using a maneuverable tablet), as well as using automated radar plotting tools (ARPA). A common drawback of the means and methods of laying is that they contain a hypothesis about the constancy of the elements of the movement of targets after they have been determined.

The way out of this situation was the introduction of automatic identification systems (AIS), i.e. systems with an active response containing information about the elements of the vessel’s movement, its classification and status in accordance with COLREGs-72. This eliminates the need to determine the elements of the movement of targets and accelerates the appearance of information in an explicit form with a high degree of reliability.

Electronic charting navigation and information systems (ECDIS ), when connected to them by radar / ARPA, allow:

– identify target speed vectors;

– identify the paths of goals;

– write down the paths of the targets;

– play the selected maneuver;

– correct the ship’s coordinates using the reference taken from the radar/ARPA;

– when connecting the AIS, interpret the received data.

The automatic radar plotting tool implemented in ECDIS processes information with a resolution that is no worse, and often better, than a stationary ARPA. Errors in determining the parameters of targets are determined by the errors of information sensors: radar, gyrocompass and log. In turn, the selected objects of the system electronic navigation chart (SENC) can be displayed on the radar indicator screen. At the same time, the SENC information displayed should include the following objects: coastline, safe contour of own ship, navigational hazards, coastal and floating aids to navigation.

Thus, ECDIS provide continuous and objective monitoring of the position and movement of the vessel and observed targets, allow automation of measurements and their processing, provide the navigator with clear and reliable information in a form suitable for immediate use.

As a result, on a navigational watch, the navigator is freed from performing many routine operations, which eliminates the possibility of making mistakes. The system provides him with information in an integrated form that characterizes all aspects of the navigation process, which makes it possible to improve navigation safety and make informed decisions on ship management.

5.3. QUANTITATIVE CRITERIA OF NAVIGATION
NAVIGATION SAFETY

International Maritime Organization Navigation Accuracy Standard . In maritime navigation, the navigational method of navigation is the main one, which consists in the continuous keeping of dead reckoning and in the regular determination of the position of the vessel.

Constant control over the location of the vessel, knowledge of its exact geographical or route coordinates at any time is the key to trouble-free navigation and successful completion of the voyage. If location determinations are performed often enough or continuously, which is possible with their automation, then the reckoning acquires a reserve value. In all cases, navigational safety depends, first of all, on the frequency and accuracy of determining the position, as a result of which determining the position of the vessel is referred to as the main task of navigation. The solution of this responsible task at sea lies with the officer in charge of the watch, who, in accordance with his duties, bears full responsibility for the safety of navigation.

More than a third of all ship accidents are strandings, and such accidents more often than others lead to the loss of the ship, many of them have tragic, and some – catastrophic consequences. To prevent such accidents, along with other measures, attempts are being made to standardize the requirements for the accuracy and frequency of observations depending on navigation conditions.

The navigator service on the ship is organized and headed by the captain of the ship and is intended to ensure navigational safety of navigation.

The presence of a ship at sea is constantly associated with its stay in certain difficult navigation areas. At any time during the navigation of the vessel, navigational safety of navigation must be ensured, i.e. the condition must be met

D but > 0,

where Dbut is the distance to the navigational hazard.

To ensure the navigational safety of the ship when sailing
from the moment of departure to the moment of arrival, navigation laying should be constantly maintained, which includes dead reckoning, determination of the position of the vessel and calculations of maneuvers for divergence from other vessels.

The process of measurement and processing of navigational parameters is accompanied by errors, which will burden the coordinates of the ship’s position. Therefore, in order to ensure the navigational safety of navigation, to justify the maneuver of the vessel in order to diverge from the navigational danger, it is necessary to assess the accuracy of determining the position of the vessel.

The assessment of the ship’s position accuracy should be made:

– when performing preliminary laying;

– when approaching the coast, navigational danger, constrained waters;

– in cases where the discrepancy of the observed place exceeds the allowable value.

The interval between observations, depending on the navigational conditions of navigation, is set by the captain of the ship.

To prevent navigational accidents associated with groundings, a subcommittee of the International Maritime Organization (IMO) developed a standard for navigational accuracy and adopted it in Resolution A.529 (13) on 11/17/83.

The standard is intended to develop requirements for the accuracy of navigation, ensuring navigational safety of navigation with a given probability ( Pbp = 0.95), evaluating the performance of systems and aids to navigation equipment (SNO) and technical aids to navigation (TSN), as well as evaluating the work of navigators.

The factors influencing the requirements for the accuracy of navigation are: the speed of the vessel, the distance to the nearest navigational danger, the navigation area.

The navigation of the vessel is carried out in three specific, in terms of the presence of navigational hazards, areas:

– the open sea;

– coastal navigation;

– constrained swimming.

In accordance with the requirements of the accuracy standard when sailing in open sea areas and coastal waters at a speed of up to 30 knots, the error of the calculated (current) position with a probability P = 0.95 should not exceed 4% of the distance to navigational danger, and at the same time its maximum value should be no more than 4 miles:

M T <0.04D but .

The IMO standard includes a table containing requirements for the accuracy of determining the location M 0 , the allowable sailing time according to the dead reckoning t d depending on D, but provided that the gyrocompass and log comply with the IMO requirements, the calculation was not corrected, the errors have a normal distribution, and the current and drift are taken into account with the possible accuracy (Table 5.1).

Table 5.1. International standards for navigational accuracy

Minimum distance to the nearest navigational hazard D but , miles Permissible radial error of the ship’s position R d with a probability of 95%, miles Radial error of the observed position of the vessel R0 with a probability of 95%, miles
<0.1 0.1 0.25 0.5 1.0 2.0
The minimum allowable time interval between observations t d , min
0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 – – – – – – –

The requirements of this standard are indicative in nature, as they are based on average estimates of the accuracy of the calculation.

The later IMO Resolution A.815(19) defines the following accuracy standards for knowing coordinates in constrained waters and on approaches to ports with a modern satellite navigation system on board: the permissible value of the error in determining the location is not more than 10 m (with a probability of 0.95) , the discreteness interval for updating coordinates is no more than 2 s.

The IMO recommendations make it possible to implement a unified approach to determining the requirements for navigation accuracy and contribute to improving the safety of navigation of ships.

In areas of constrained navigation, where the position of the ship is controlled by observations using coastal landmarks and radio navigation systems, the requirements for navigational accuracy depend on the specific circumstances of navigation.

To ensure navigational safety of navigation, it is necessary to make the following calculations:

– evaluate the probability of safe navigation Р bp for specific navigation conditions;

– in the case when R bp < R ass , it is necessary to calculate the allowable RSKP of the numbered place M d depending on R ass ;

– choose methods for determining the ship’s position that satisfy the condition М 0 < M d ;

– calculate t d for specific methods of determining the position of the vessel;

– calculate the discreteness of observations Δt 0 = t d – 2t obs ;

– build a graph of changes in M d and M t over time for individual sections of the transition route.

The navigational safety of navigation Р bp is estimated by the probability of a ship passing through clear water without contact with surface and underwater obstacles with known coordinates.

To calculate Pbp when navigating among navigational hazards located in different directions in the coastal zone, the Rayleigh circular distribution function is used

Pbp = 1 – exp (D/M) 2

where D is the shortest distance to the nearest navigational hazard; M – RCMP of the calculated position of the ship at the point of the shortest distance to the nearest navigational danger.

The calculation of R bp is made using the table. 4.18 MT-2000 for arguments D and M.

Table 4.18 can be used to calculate M d for a given D min according to a given probability of safe navigation P bp , as well as to determine the minimum allowable distance to navigational danger D min with a known RAIS of the ship’s numbered position M and a given probability of safe navigation R bp .

If navigational hazards are located on one side, then the probability of safe navigation:

P bp u003d 0.5 [1 + Ф (Z)],

where Ф(Z) is the Laplace function determined by the argument

Z = D√2/M

And in this case, for calculations, you can use the collection MT-2000, entering the table. 4.19 for arguments D and M.

With the advent of the pilotage method of navigation, a simple and immediate quantitative safety criterion arose – a safe distance, which is understood as the minimum distance measured or determined by eye between the vessel and the danger. Based on experience and common sense, as well as science, the most likely and dangerous in terms of consequences is a meeting with dangerous objects located at sharp heading angles of the ship (Table 5.2).

Table 5.2. Probability of appearance of objects, % depending on the ratio of velocities V H /V 0 and heading angles of the vessel

Heading angle Speed ratio 0-30 about 30-60 about 60-90 about 90-120 about 120-150 about
0.5 1.0 2.0 4.0∞ 50.2 44.8 40.6 30.0 24.4 16.7 37.1 32.7 31.6 25.0 22.0 16.7 12.7 16.2 17.7 19.4 18.2 16.7 5.1 7.9 12.4 14.0 16.7 1.2 2.7 7.4 11.4 16.7
Notes: 1. V H – the speed of the observer, V 0 – the speed of the object. 2. The probabilities of the appearance of objects in the stern, within 150-180 about , are insignificant values (with a ratio of speeds from 1.0 to 4.0), respectively, 0.5-10.0%.

From here it is possible to determine the values of safe distances D b for discrepancy with the detected immovable hazards:

– when avoiding danger by active or passive braking of the vessel

D b ≥ D 0 – VΔt – S t – m D – m S , (5.1)

where D0 is the hazard detection distance; V is the ship’s speed until the start of the evasive maneuver; Δt is the dead time interval when the machines are maneuvering; S t – stopping distance of the ship until it comes to a complete stop; m D – limiting with a given probability error in determining the distance to the danger; m S – limiting with a given probability error in determining the stopping distance;

– when avoiding danger by turning the vessel

D b ≥ D 0 – R – VΔt – S t – m R – m D, (5.2)

where Δt – dead time during the implementation of the turning maneuver; R is the radius of the actual circulation of the vessel (taking into account its dimensions); m R – marginal error with a given probability of determining the real radius (diameter) of the ship’s circulation.

In accordance with the requirements of good maritime practice, as well as the rules regulated by IMO Resolution A.601 (15) dated 11/20/87

“Representation on ships of information about their maneuvering characteristics”, errors in determining the stopping distance and run-out of the vessel, as well as the circulation diameter, should not, with a probability of 0.95, exceed values constituting 10% of the inertial-braking characteristics themselves.

The situation related to safe distances relative to moving objects (other ships) is more complicated. If we proceed only from the premises of common sense, then in this case the distances given in formulas (5.1) and (5.2) should be doubled.

International and national requirements do not categorically define the values of safe distances when passing from other vessels. However, Rule 6 COLREG-72 defines the concept of “safe speed”, without giving quantitative characteristics. In our opinion, the experience of the past cannot be neglected. In the interpretation of the requirements of Rule 16(a) RPSS-60, the term “moderate speed” meant the speed of the ship, at which its stopping distance should be at least 0.5 of the visual detection range of another ship under given visibility conditions. In order to automate the control of the ship in the absence of other criteria, this approach can be recommended. In accordance with accepted international and domestic practice and the requirements of Rule 3 of COLREG-72, limited visibility is considered visibility of less than 3 miles. This distance is taken as safe when sailing on the high seas, decreases to 2 miles in the coastal zone and is 1 mile when sailing in cramped conditions.

When visibility is less than 5 miles, it is prudent to at least keep the car ready to reverse. But it also depends on a number of other factors that are not related to visibility, for example, the navigation area, own speed and stopping distance, the efficiency of using radar information, etc. Thus, a speed selected with a visibility of 5 miles in the ocean, where an encounter with small craft is unlikely, cannot be considered safe in narrow places, or in an area of heavy traffic, or in a fishing area, etc.

When navigating through systems of divided traffic, when ships are traveling in the same direction, the safest speed will be the “stream speed”, corresponding to the average speed of other ships.

Thus, the above quantitative criteria for navigation safety should be guided by the choice of means and methods of marine navigation, when equipping ships with navigation and control tools, to formalize the criteria laid down in the logic of analyzing navigation information using a computer, and also to determine the principles of organizing a navigational court services.

Requirements of the International Association of Lighthouse Authorities. When sailing in cramped areas, in narrow spaces, along traffic separation systems, canals, fairways, the requirements for navigation accuracy are increased and more detailed than the IMO requirements.

The International Association of Lighthouse Authorities (IALA) regulates the calculation of Pbp using the normalized Laplace function, which can be selected from Table. 4.20 MT-2000.

1. In the general case, when the line of a given path (LZP) is laid at distances D l and D 2 from the borders of the strip along which the vessel follows, the probability of safe navigation is calculated by the formula

P bp u003d 0.5 [Ф (Z 1 ) + Ф (Z 2 )],

where Ф(Z i ) – normalized Laplace function;

Z i u003d D i / 0.7M T – normalized distance to the danger, expressed in standard deviations;

D i is the distance to the nearest lane boundary;

0.7M T is the root-mean-square error of the ship’s position in the direction perpendicular to the track.

2. In the case when the LZP is laid in the middle of the strip, i.e. D 1 u003d D 2 u003d u003d 0.5H

(H is the width of the ship’s lane along the traffic separation system, fairway, channel):

F (Z 1 ) u003d F (Z 2 ) u003d F (Z),

where Z u003d 0.5N / 0.7M T u003d 0.7 N / M T ,

P bp u003d F (Z).

Table use 4.20 MT-2000 can also facilitate the solution of the inverse problem, when, in order to provide a given probability of safe navigation P bp , it is required to calculate the allowable RCWP of the ship’s position M d .

Laying LZP in the middle of the narrowness is most preferable, since in this case P bp = max.

3. In accordance with rules 9 and 10 of COLREGs-72, when a ship is navigating in narrowness, along the NRS, on the fairways, along the channels, the boatmaster should, as far as possible, keep to the outer boundary of the passage on the starboard side.

If, when swimming in the middle of the narrowness, R bp u003d 1 or R bp > R ass , then you should calculate the minimum distance D min at which the LZP can be laid relative to the outer limit of the narrowness.

When sailing along one navigational hazard (one border of the passage), when the distance to another navigational hazard is D 2 > 3M T and P 2 = 1, the probability of safe navigation

P bp u003d 0.5 (P 1 + 1),

where R 1 u003d F (Z 1 ) u003d F (1.4 D 1 / M T ).

When solving a similar problem, the work is simplified if you use the table. 4.23 MT – 2000.

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