JAPAN P& I CLUBVol.34 March 2015

P&I Loss Prevention Bulletin
The Japan Ship Owners’
Mutual Protection & Indemnity Association
Loss Prevention and Ship Inspection Department

Bridge Watchkeeping and
Collision Avoidance

Table of Contents
Introduction…………………………………………………………………………………………………………… 2
ARPA – Risk of Collision…………………………………………………………………………………………… 3
ARPA – Action to avoid collision… ……………………………………………………………………………… 6
Collision Avoidance with AIS … ………………………………………………………………………………… 7－1－

JAPAN P& I CLUBP&I Loss Prevention Bulletin

Introduction
Fifty years ago it was generally acknowledged that the introduction of radar on board commercial
ships did not have the dramatic effect of reducing the numbers of collisions which was expected.
When automatic radar plotting aids (ARPAs) were launched on the shipping community, there wasconcern that the industry would have difficulty in providing the advanced training necessary to enable
operators to use the equipment properly and safely. Now we can say that, despite considerable investment in training and, even though the equipment has
been available to almost all navigators of seagoingcommercial ships for many years, the advanced
computer technology of the ARPA has not rendered
the ship collision a thing of the past.
In recent years, as a further aid to collision avoidance watchkeeping, the navigator has been given
the Automatic Identification System (AIS). This
technological advance provides the navigator withthe ability to identify another ship by name. Also, inmany cases, information transmitted by other ships
in the area is displayed on the radar screen and onelectronic charts (ECDIS) so that the navigator canview that “live” data.
Throughout this period of technical advancement,
government authorities worldwide have warned
that over-reliance upon a single electronic aid is a
primary cause of collisions. It is a fact that somenavigators on ships fitted with the most sophisticatedcollision avoidance systems are so captivated bytheir electronic displays, and the movement of targets
across their screens, that they routinely fail to lookout of the bridge windows to make a proper visualappraisal of what is going on around their ship!

AIS

ECDIS

We will discuss in this article the use of ARPA and AIS, the information they give the navigator andwhat it means, with some reminders of the International Regulations for Preventing Collisions at Sea
1972 (COLREGs) and then give some thoughts to be considered and some guidelines which should be
followed.

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JAPAN P& I CLUB

ARPA – Risk of Collision
The introduction of ARPA provided a significant advance in collision avoidance because any risk of collision with any of the otherships in the area is constantly assessed by computer technology andthe results are displayed for the navigator to use. That is, of course,
provided they are plotted or automatically detected. This technology has brought into focus the fact that it is necessary to determine
the distance off at the closest point of approach (CPA) of anothership in order to establish whether or not there is a risk of collision
with that other ship.
However, although the results of the computer calculation areprovided so that the navigator can evaluate the situation, thoseresults are in absolute terms, to two decimal places, such that the
CPA shown on the display is a simple numerical value; for example
0.16 miles.

?

Question

ARPA?

Do you plot all the targets on the radar screen, those which arewithin a certain range or only those which might affect your passage,or do you just rely on AIS targets?

??

The display of CPA distance provided by an ARPA has seductive qualities. It usually provides a convincingly precise result
which might appear entirely unremarkable. That is, unlessthe navigator has activated a closest point of approach alarm,in which case a distinctive marker is displayed on the screen
and, if the CPA distance is less than the alarm set distance, an
alarm will not sound. Invariably, if the CPA distance is lessthan the passing distance required by navigational practice on
board (for example as given in the master’s standing orders
or in night orders) but is nevertheless positive, the navigator
will be tempted to accept that CPA distance as being safe andRadarwill then be tempted to reduce the margin of safety for theparticular situation. He justifies this action by convincing himself that the computer has advised him that, although
the CPA distance is less than the minimum passing distance given in standing orders, the passing distance of the ship
being plotted remains positive and therefore no risk of collision exists.
The belief that an ARPA can tell the navigator that no risk of collision exists is
entirely false.

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JAPAN P& I CLUBP&I Loss Prevention Bulletin?

Question?

What is the minimum passing distance given in standing orders on
board your ship? When using an ARPA do you activate the closest
point of approach alarm and, if you do, what range do you use?

??

An ARPA does not have the intelligence to consider all of the circumstances
which are involved with a close quarters situation, and cannot evaluate all of
the contributing factors in order to carry out a full risk assessment. It does nothave the ability to consider possible future events, weather conditions, steering
accuracy, safety contingency, traffic situations, navigational situations or, as
important as any of these, peace of mind! It can only make a calculation based on
past information.
In the days before ARPA, in almost all clear weather encounters with shipping traffic, navigators relied upon visual
bearings of an approaching ship to determine whether or not there was a collision risk. In the appraisals made in thosedays, the value for CPA was assumed to be either "zero" or "sufficient" depending upon the rate of change of observed
relative bearings. One of the advantages of such a visual assessment is that the visual check requires the navigator to
become physically involved with the dynamics of the situation. That is, by following a procedure as follows:Using his eyes and an azimuth mirror, shadow pin and other equipment on a compass
repeater on a number of occasions to obtain a series of relative bearings of the other shipand noting those bearings down.

By sighting the navigation lights, or the masts/cranes, to estimate the aspect and approximate heading of the other ship.

By observing the display presented on the radar screen to obtain the range of the othership and the closing speed.

This process makes use of
the watchkeeper's senses ina broad appreciation of thesituation. The process is still
relevant and should be used
when appropriate today.

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JAPAN P& I CLUB?

Question??

?

Do you routinely take visual bearings of an approaching ship toestablish whether or not risk of collision exists?

The CPA in pre-ARPA days on board most ships was generally never less than 0.5 mile in open waters. The
watchkeeper determined the CPA distance by applying his knowledge and experience, and by using a combinationof visual bearings and observations, and the simple technology provided by radar range rings or the variable range
marker and a bearing cursor. By use of these methods, the navigator was sure that either (a) the other ship would passwith a distance off his own ship greater than the minimum passing distance given in the standing orders, or whatever
he considered safe in the prevailing circumstances, without any action being taken, or (b) the distance off would not
be a safe distance and therefore action was required.
The advantage of the pre-ARPA appraisal techniques was that, in a sense, it was consistent with the requirements ofRule 7 (a). "If there is any doubt such risk shall be deemed to exist".
Checking for a risk of collision by visual bearings as described above produces two benefits:-

1

First, there is a requirement to start
the process of assessing whether or
not a risk of collision existed early because
there is a need for a series of bearings to betaken in order to obtain a reliable answer.

2

 econd, the assessment in most cases
Sdoes not take account of fine detail orsmall margins. That is, if a small change
in bearing occurs, this must be treated asif there is no change of the bearing at all.

There can be no doubt that an ARPA provides the watchkeeper with a powerful tool for studying and analysing the
movements of ships in the immediate sea area around his own ship. However, being a computer, an ARPA, on the
one hand, is only capable of making calculations, whilst on the other hand the results of those calculations will have ameasure of precision far and beyond that which is strictly necessary or justifiable for ordinary navigational purposes.
It is that computer ability to cheerfully predict CPA distances to an accuracy of 0.01 mile, and to therefore predict
actual CPA distances as small as 0.01 mile, that provides one of the pitfalls which, unfortunately, occasionally brings
about disaster. Remember that 0.01 mile is 1/10th of a cable or 18 metres and also that the antenna is above the bridgewith the bow possibly 300m, 1.6 cables or 0.16 miles, ahead of the bridge, so that a CPA distance of 0.25 miles could
lead to a collision.
Furthermore, the convincingly precise display presented by an ARPA can instil confidence to the extent that thenavigator feels he can relax and delay a collision risk appraisal, he feels he can maintain full speed in congested waters
and/or he can delay a collision avoidance manoeuvre until the range of the other ship has closed to some extent.
However, this often results in the development of a close-quarters situation where only a large alteration of course will
be enough to avoid collision. The navigator may know precisely what tracks other ships have been following at an
earlier stage, but that knowledge must be used in such a way that action is taken in ample time in accordance with therequirements of Rule 8: Action to Avoid Collision.
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JAPAN P& I CLUBP&I Loss Prevention Bulletin?

Question?

Do you use the ARPA properly to take early action to avoid potential
close-quarters actions in multiple vessel situations, or does it give you
confidence to navigate at passing distances and speeds closer and fasterthan you would if you did not have it?

??

The computer may provide accurate information on the situation around a ship but this does not provide the navigatorwith the freedom to navigate close to or within the margins of safety. In fact, the exact opposite is the case; the large
amount of information should permit the navigator to take early action when appropriate and to improve his collision
avoidance strategy for overall navigational benefit, always bearing in mind good seamanship practice.
The following are guidelines to be followed for successful watchkeeping with ARPA:-

1

2

Appreciate that the ARPA
display cannot tell you that there
is no risk of collision.

3

Recognise that the information provided by the
ARPA does not permit you todelay taking collision avoidance
action.

Understand that the information provided
by the ARPA does not allow you to reducethe minimum allowed CPA distance to less than isconsidered safe by the master, and as instructedin his night orders and standing orders.

4

Do not rely only upon the information givenby the ARPA display and, when appropriate,use a series of individual bearings to assess
whether or not there is a risk of collision withanother ship.

ARPA – Action to avoid collision
The navigator of the pre-ARPA days was aware of one important factor; that is, unless he was in restricted visibility,
he was navigating his ship on a visual basis and so too were all the navigators of other ships he could see. For thatreason, good navigators had an appreciation that any alteration of course had to be large enough to be readily apparent
to the navigator of the other ship. By day, this was done by reference to the alignment of ship's masts/cranes, whilst atnight this was done by applying knowledge of the aspect of the navigation lights. For example when altering course to
starboard for a ship crossing ahead (under Rule 15: Crossing Situation), a navigator would make sure that he changed
his ship's heading sufficiently to bring the other ship from his starboard bow onto his port bow so that he changed theview of the masts/cranes by day or at night changed the navigation light displayed by his own ship towards the otherfrom green to red.
The proper use of visual references made actions unambiguous.

－6－

JAPAN P& I CLUBA navigator using an ARPA is tempted to make an alteration of course which will simply bring about a prediction of
the safe passing of the other ship by achieving the required mathematical result on the computer. That is to say, hewill make an alteration of course which results in the predicted CPA distance, as calculated by the ARPA, being equal
to the minimum required CPA distance. This may, or equally may not, result in a change in the aspect of the masts/
cranes or navigation lights, or as a change in target trail on a radar screen which can be seen by the navigator of theother ship. If the COLREGs are adhered to, then the alteration should be large enough to be observed visually or byradar. It is important to remember that an alteration of course of less than 10o is unlikely to satisfy the requirement.

?

Question?

What change in the ship's heading is the minimum acceptable
alteration of course under normal circumstances so as to be readily
apparent to others?

??

The need to comply with the meaning of Rule 8: Action to Avoid Collision - that, is making action taken "large
enough to be readily apparent" to the navigators of other ships - becomes critical when circumstances require that
manoeuvres must take place at close range, for example, when the distance between ships is less than 3 miles.
This might, for instance, arise in a multi-ship encounter in a strait where a ship is avoiding crossing traffic. Here, the
ARPA may be of assistance in judging where there will be a gap in a traffic flow sufficient to permit a safe manoeuvre. When such a situation has been identified, the navigator must focus all of his attention on the manoeuvres to beundertaken. In this type of situation it is imperative that all action taken is unambiguous to a navigator on another ship
and this means the heading must be altered so that the aspect of the ship in daylight or the navigation lights at nightchange significantly.

Collision Avoidance with AIS
When they were first introduced, Automatic Identification Systems delivered a whole new layer of information onto
the navigation bridge. The technology provides the navigator with the identification (name, call sign and MMSI
number) of other ships in his immediate sea area. The data received also includes the heading, speed and position of,and some additional information about, the other ships.
When AIS was launched on the shipping industry in the 1990s, some representatives of the electronics industry werepredicting that the system had the potential to replace radar as the principal collision avoidance aid. In 2000, IMO
adopted a new requirement for all ships to carry Automatic Identification Systems capable of providing information
about the ship to other ships and coastal authorities automatically. Since 2004 the equipment has been a compulsory
provision on board all ships of 300 gross tonnage and upwards engaged on international voyages, on board cargo shipsof 500 gross tonnage and upwards not engaged on international voyages and on board all passenger ships irrespectiveof size.
The greatest beneficiaries of AIS information are the shore stations, and coastal and port authorities, because thesystem allows identification of traffic approaching ports or transiting straits. The system compliments traffic surveillance systems and is of considerable assistance when issuing traffic guidance messages and warnings, and for search－7－

JAPAN P& I CLUBP&I Loss Prevention Bulletin

and rescue purposes.
As far as the navigator on board ship is concerned, the eye catching benefitof the AIS is that the names of ships which are in his vicinity can bepresented on the ARPA screen. It was considered that, in theory, this would
be of considerable assistance when deciding upon an appropriate collision
avoidance strategy. The fundamental question here is, however, in reality:
Does the enhanced knowledge of target identity make the task of avoiding acollision any easier?
VHF

Discussing intentions with a clearly identified ship at an early stage can,without doubt, and in certain circumstances, be an advantage. Examples of this type of encounter might include
overtaking in a narrow channel and meeting a ship in a river with bends. However, these events are only a relatively
small proportion of the total of all ship encounters around the world.
As far as the relationship between individual ships in any encounter is concerned, it is the International Regulations
for Preventing Collisions at Sea 1972 that must be complied with in every case. Navigators should not need to bereminded that there is no provision in the COLREGs either for use of AIS information or for contact to be madebetween ships to allow actions to be discussed. There are very good reasons for this.
If a navigator has any doubt as to whether or not VHF contact to discuss collision avoidance strategy is a valid option,
he should, for a moment, imagine himself in a busy seaway off an archipelago which is crossed by both local andinternational traffic. He should consider, for example, how many different nationalities of watchkeeping personnel
there might be on the bridges of ships which are within the range of his radar. He should then think about the possible
standard of English spoken by those many watchkeepers and bear in mind that some of those watchkeepers might
have only poor, broken English and that others, particularly the watchkeepers on board coastal ships, might have no
English at all.

?

Question?

Before you call another ship on VHF ask yourself: what do you hopeto learn that cannot be obtained by plotting its target and following
the COLREGs? If you are in doubt about another ship's intention, use
the appropriate sound and light signals.

??

He might also like to consider how the name of his ship might be pronounced, and how the names of other ships in thearea might be pronounced by the navigators on the bridges of other ships. He might then reflect on his experiencesof trying to identify calls - which were not instantly comprehensible - from port control operators spoken in broken
English.
The navigator should also then consider what evidence he has that the voice he can hear on the radio when contact
is established is the voice of the navigator on the bridge of the ship he has identified from the AIS. There are many
parts of the world where abuse of the radio frequencies remains a very serious problem and where coastal authorities
are powerless to take any action against those abusers. Finally, the navigator should contemplate the effects of all the－8－

JAPAN P& I CLUBforegoing if, through neglect, he is making a desperate attempt to contact the navigator of another ship because of his
own failure to take early action to avoid a close quarters encounter.
The following are guidelines for successful watchkeeping with AIS:-

1

2

 IS should not be consideredA
as a device to encourage communication between ships’
navigators.

 IS information has the sameA
status as ARPA information,and it should be treated as an
information display system.

Finally, some simple good seamanship practice:-

good seamanshipA

You know
the COLREGs, they
provide guidance for theprevention of collisions in
all circumstances, so
use them.

Ｃ

Ｂ
Understand what the ARPA
display and the AIS can provide
and what they cannot provide they cannot tell you that there isno risk of collision.

Do not rely upon one aid tonavigation; use the ARPA in conjunction with visual bearings, and any othermeans, to establish if a risk of collisionexists. If there is any doubt, such risk
shall be deemed to exist and appropriate
action must be taken which is inaccordance with the COLREGs.

Ｆ

ＤＥ
Keep a good lookout. Watch
the other ships in the area there is no substitute for theMark I eyeball.

Always make alterationsof course large enough tobe observed visually or byradar.

Do not ever forget that themain engine is there to be
used - slow down or stop if
the circumstances require.

Safe Watchkeeping－9－

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