Maritime University of Szczecin
Akademia Morska w Szczecinie
2008, 13(85) pp. 54‐58 2008, 13(85) s. 54‐58
Use of modern radars in order to maintain navigation safety
in restricted water areas
Wykorzystanie współczesnych radarów w celu zapewnienia
bezpieczeństwa nawigacji na akwenach ograniczonych
Evgeniy Lushnikov
Akademia Morska w Szczecinie, Instytut Nawigacji Morskiej
70-500 Szczecin, ul. Wały Chrobrego 1–2, tel. 091 48 09 402, e-mail: gena@am.szczecin.pl
Key words: base leading line, safety of navigation, compass error, accuracy of navigation, radar navigation Abstract
The method of manual and automatic definition of the compass error with the help of radar has been described. The article presents the mathematical description of accuracy of the offered methods and the ways of increasing the accuracy.
Słowa kluczowe: nabieżnik bazowy, bezpieczeństwo nawigacji, poprawka kompasu, dokładność
nawiga-cji, nawigacja radarowa
Abstrakt
Opisano metody ręcznego i automatycznego określenia poprawki kompasu za pomocą radaru. W artykule za-prezentowano opis matematyczny dokładności proponowanych metod oraz sposoby zwiększenia dokładno-ści.
Introduction
The most widespread kind of vessels emergency is a grounding. It is very often owing to uncon-trolled work of gyrocompass.
Such serious accidents of the 20th century were
destruction of a supertanker “Torrey Canyon” and pollution of 120000 tonn of oil to the south beach of England at rocks of Silly. This accident, evalu-ated as national tragedy of England, was the result of the undetected refusal of a gyrocompass at navi-gation in fog. The regular control of the compass error is one of the major tasks of the navigator. Even the form of the logbook compels the naviga-tor to watch at least 4 times the value of compass error accepted to the account. For determination of the compass error time and presence of opportuni-ties are essential. In this connection, the same value of a compass error very often corresponds from
watch to watch, day by day and even from week to week.
Fig. 1. Grounding and destruction of a supertanker “Torrey Canyon” in English Channel caused by a hidden defect of a gyrocompass during fog
Rys. 1. Osadzenie i zniszczenie superzbiornikowca „Torrey Canyon” w Kanale Angielskim spowodowane ukrytym defek-tem kompasu żyroskopowego podczas mgły
Not always does such a state mean carelessness of navigators. It shows that navigators during watch have a set of other, not less responsible and urgent duties. The duty of continuous supervision over surrounding conditions, management of a vessel and performance of industrial operations are their direct purpose. Similar operations are scientific and hydrographic measurements, search and rescue operations, fishing operations, military manoeuvres etc.
Reasonable arrangement of priorities of carried-out operations is an extremely complicated task. There is no solution of this task on strictly scientific basis. For this reason, the navigator puts priorities and chooses the order of actions proceeding from the developed situation [1].
In navigation in narrow waterways and in re-stricted water areas, the navigator frequently uses floating marks. These marks are potentially more dangerous than stationary marks, as there is a real opportunity to drift from anchor position. Such an opportunity demands from the navigator enhanced attention and control over the use of these protec-tion means that demands addiprotec-tional time, methods and means.
In the choice of means and methods for deter-mination of a task, the navigator takes into account time expenses for performance of operation. If the means or a method take a lot of time, he will never be granted any high priority. If the means or a me-thod demand knowing and remembering a lot of the complex information, such a method or means can not apply for a high priority either. All this speaks for limitation of time and resources.
Modern means and methods of monitoring a compass error
The appropriate control of the compass error over voyage can be executed in the presence of corresponding opportunities.
Frequently, the compass error is determined by a leading line when the vessel leaves or enters the port. For exact determination of the compass error it is necessary that the observer is situated precisely on a leading line at the moment of supervision, and a vessel is close enough to leading marks. Devia-tions from the leading line occur often and result in an additional error of supervision. Other means and methods have specific problems and restrictions as well.
The use of the AIS system demands providing the solution of the problem of bearing simultaneity, the account of antenna location of a counter vessel and a place of arrangements of compass repeater.
Visual methods of navigation with the use of superfluous bearing, horizontal angles, etc. demand essential time expenses and solution of the simulta-neous supervision problem.
Astronavigating ways with the use of astronomy bodies are very complex and they demand much time for supervision and calculations.
A very essential factor is the fact that all these methods demand good visibility, which is rather rare.
Absence of visual visibility can explain, but not justify, the absence of the control. Navigator’s task in these conditions is to provide monitoring of a compass error as quickly as possible.
From all the means that the navigator has in conditions of bad visibility there is a unique oppor-tunity – a radar.
The use of a radar-tracking picture for the de-termination of a compass error can be executed within the framework of the classical method. This method assumes the mapping of a fix position free from the influence of a constant compass error with the subsequent determination of the true bearing and its comparison with the compass bearing from the radar. Here the observation can be executed by transition from three radar bearings to two horizon-tal angles etc.
All these methods of navigation created for a ra-dar picture complicate without long-term proce-dures. For this reason, such an opportunity in navi-gation in waterways, where frequently the account goes for seconds, has not received wide practical application.
The determination of the compass error always assumes presence of a reference direction, whether it is a leading line, a base leading line or a known true bearing of reference points. Leading line and base leading line can be used only when the vessel is on this leading line and even small deviation from it complicates the process.
Basically, the leading line of position represents [2, 3] deterioration of an isogon for a horizontal angle between reference points which equals zero. The opportunity for exception of bearing mistake is obtaining in this case as a charge for loss of oppor-tunity for position's fixing by these two marks.
The fundamental requirement of navigation for definition of the compass error is that a vessel should be on a leading line and at a distance provid-ing appropriate accuracy.
Rapid development of radar equipment enables expansion for a class of tasks created with the help of a radar. Practically nothing prevents the use of a radar picture as the navigation chart. This is pro-moted by the option in modern radars that allows to
render for a radar picture the direct marker lines focused on the set direction and in the set distance from the center of the screen. This option allows to solve enough challenges in a very simple way.
Let us assume that on the screen of a radar two dot objects are observed and coordinates of these objects are known with high accuracy on a map. In this case, true bearing TB of leading line is formed by objects as it is known with high accuracy. If the observer was on this line, he could, by this leading line, determine the compass bearing CB and also calculate the compass error ∆K with the use of the following formula:
CB TB K= −
∆ (1)
The arbitrary direct line on the radar screen can be transfer in parallel to himself to centre. This line shows on the screen of radar the compass bearing CB . This bearing is according to bearing of base leading line (see fig. 2).
Fig. 2. Determination of compass bearing taking place side-ways of base leading line
Rys. 2. Określenie namiaru kompasowego odbywającego się z boku podstawowej linii nabieżnika
The curvature of the earth can be ignored as the factor of accuracy at rather small distances.
In modern radars, such as Norcontrol’s “DATA
BRIDGE 2000”, Kelvin Hughes’ “NUCLEUS” and
others, there is an opportunity to indicate up to 50 parallel lines oriented in the set direction. These lines allow to determine the compass bearing of any leading line not being on it.
The absence of complex calculations and of re-strictions is very important merit for monitoring of gyrocompass.
The method does not demand a specially estab-lished leading line nor a presence of these marks on this line.
It is obvious that the final answer to the question of practical suitability of any method can be
received only when the question of accuracy of an offered method has been investigated.
Accuracy of the compass error determination by radar
At small distances between observable reference points (as it takes place at the classical visual lead-ing line), supervision is inexpedient owlead-ing to the lower sensitivity than at the visual leading line. Here, it is necessary to choose objects for supervi-sion on the greatest possible distance between them and to choose a scale for supervision so that sub-jects are as close to the opposite edges of the screen as possible. A limiting case of such a situation is navigation by base leading line. The navigation by line of boyages designating an axis of a waterway is the most typical case of navigation by base leading line [4].
In navigation by base leading line small devia-tions from an axial line are assumed. Determination of the compass error in the set situation depends on how precisely a readout of direction of a base line can be determined. As the basic source of errors is the error of measurement of directions, it is possible to count distances D1 and D2 as correct values. The
error of measurement of compass bearing mCB is
shown in figure 3.
Fig. 3. An error of measurement of compass bearing by radar at base leading line
Rys. 3. Błąd pomiaru namiaru kompasowego przez radar na podstawowej linii nabieżnika
Having taken such assumptions into account, the error of determination of compass bearing CBr by
radar can be written down as [3]:
CB CB CB CB m D D D D D D m D m D m r + ⋅ + = + + = 2 1 2 2 2 1 2 1 2 2 2 2 2 1 (2)
From the formula (2) follows that at the begin-ning and at the end of base leading line (in immedi-ate proximity to marks), accuracy of determination
of the compass error will be determined by the ex-pression: CB CB m m r = (3)
In the middle of base leading line the accuracy will make: CB CB CB , m m m r = 2 =07 (4)
Thus, we see that the accuracy of definition of the compass error depends on accuracy of determi-nation of bearing readout for a leading line at which the maximal accuracy takes place in the middle of a base line.
As the measurement is carried out very simply during a few seconds, it is possible to provide su-pervision for increasing the accuracy.
The role of the base leading line is that it can carry out not only navigation marks on waterways, but also the marks placed on the opposite side of channels, gulfs and rivers.
Regular radar errors do not render influence on accuracy of determination of the compass error for that simple reason that the radar picture is conform (equiangular). The scale of a radar picture in any direction is always the same as it is on a map of the Mercator projection. It means that any scale changes and changes of radar picture connected to it do not result in distortion of directions.
Control of vessel's presence in a waterway
In navigation by radar inside the waterway, even in the presence of navigational marks, the navigator estimates the position of a vessel concerning the line of the set course in a visual way. The visual estimation is of no high accuracy which does not guarantee high reliability of navigation [3, 5].
The presence of marker line in a radar allows to guarantee high accuracy and reliability of naviga-tion. Even small displacement from a line of the set
course of a vessel is easily found by a parallel line. It allows to correct operatively the ship course without the use of a plotting as it takes place in navigation by usual leading line.
The classical radar's leading line has not possi-bility for discovery of mark's drift from regular place. When using marker lines and not less than four protecting marks, there are opportunities of visual detection of boyage's drift from a regular place.
Control of buoy's position in a waterway
The parallel arrangement of the right and left lines of buoys is established by the passage corre-sponding to marker lines through correcorre-sponding buoys. When one of the buoys is situated away from a corresponding marker, it specifies its drift.
Fig. 5. Observation of drifting buoy Rys. 5. Obserwacja dryfującej pławy
The drift of marks in lateral direction from an axis from a waterway is observated more effec-tively. The observation of drift in longitudinal di-rection is much more difficult.
Conclusions
The wide usage of marker lines enables simple, fast and exact decision-making in such major navi-gation problems as detemination of a compass er-ror, deduction of a vessel in the set trajectory or the control of reliability of protecting marks.
The use of marker lines reduces the time of de-termination of navigation tasks and thus increases safety of navigation in channels, narrows and in the limited water areas.
References
1. LUSHNIKOV E.: Use of system AIS for maintenance of
navi-gating safety. International conference “Explo-Ship 2004”. Szczecin-Copenhagen 2004, 263–271.
a) b)
Fig. 4. The use of a radar marker line in navigation in a wa-terway a – the vessel is on the right from axis; b – the vessel is on the left from axis
Rys. 4. Użycie markera w nawigacji na drodze wodnej; a – statek jest na prawo od osi; b – statek jest na lewo od osi
2. LUSHNIKOV E.: Increase of navigational accuracy at sailing by leading line. II International Congress Seas and Oceans, Szczecin – Międzyzdroje, AM, Szczecin 2005, 129–138. 3. LUSHNIKOV E.: Use of base leading line for determining of
a compass error. II International Congress Seas and Oceans, Szczecin – Międzyzdroje, AM, Szczecin 2005, 139–143. 4. ЛУШНИКОВ Е.М.: Определение правки компаса при
отсутствии видимости. XV International Scientific and Technical Conference “The Role of Navigation in Support of Human Activity at Sea”. AMW, Gdynia 2006, 184–190.
5. LUSHNIKOV E.: The estimation of radars information for collision situation. Sympozjum Nawigacyjne. Nawigacja morska i bezpieczeństwo transportu morskiego. WSM, Gdynia 2005, 77–84.
Recenzent: dr hab. inż. Wiesław Galor, prof. AM Akademia Morska w Szczecinie
