International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 2
Number 3
September 2008
Combination of Navigational and VDRbased
Information to Enhance Alert Management
M. Baldauf & K. Benedict
Hochschule Wismar, University of Technology, Business and Design, Department of
Maritime Studies Warnemünde, Germany
E. Wilske & P. Grundevik
SSPA Gothenburg, Sweden
J.O. Klepsvik
Kongsberg Seatex, Trondheim, Norway
ABSTRACT: Within this paper results of ongoing investigations will be presented. Main subject of studies is
laid on the present situation of alert management onboard ships navigational bridges and potential use of data
recorded with mandatory ship-borne VDR equipment during normal ship operation to support the process of
on board collision avoidance. The investigations and results discussed and presented in the paper are gained
within trhe work in two different projects on research and technical development. The first is the European
MARNIS project on Maritime Navigation and Information Services. It is funded by the European
Commission, Department for Energy and Transport. Secondly some of the results presented here are part of
investigations performed under the national RD project "Maritime Safety Assistance Rostock" which is
funded by the German Ministry of Education and Research Berlin.
Safe navigation, including collision and grounding
avoidance, is the overall task of the navigating
officer in charge. The global aim is to ensure the safe
transport of goods during a ship's voyage from port
of departure to port of destination. Modern ship
bridges are highly-automated man-machine systems.
Safety and efficiency of the ship operations are
dependent, as in all other complex man-machine
systems, on the communication between humans and
machines during the accomplishment of tasks.
Humans can fulfil their assigned monitoring, control,
and decision tasks most effectively, if the
information flow between them and machines is
adapted to the human skills and abilities (e.g.
Brainbridge (1983) and Lützhöft, 2004).
In the last years a strong increase of modern
information systems on the ship bridges could be
observed. Simple displays and control systems were
supplemented or replaced by complex computer-
based information systems. Information of different
sensors and systems are combined in integrated
navigation systems (INS). In order to support the
mariner effectively on board, a task- and situation-
dependent presentation of the information is a
compellingly need.
With the enlarged number of systems and sensors
onboard, and the increase of automation a
proliferation of alarm signals on the bridge is
associated. Alarm signals coming from various
systems and sensors sometimes lead to a confusing
and difficult manageable situation for the mariner,
which is distracting him from his task to safely
navigate the vessel. Redundant and superfluous
audible and visual alarm announcements are
appearing on the bridge.
The International Maritime Organization (IMO)
IMO has recognised this situation and decided to
revise the exiting standards for INS and to develop
requirements for an alarm management system. A
working group coordinated by Germany was
established to progress this work. Further activities
as especially the eNavigation (Earthy, 2006a)
initiative is strongly linked to thise subject and
covers problems related to integration of systems.
Several investigations were performed to analyse
the specific situation on board ships regarding the
occurrence of alarms by means of a series of
empirical studies. Basing on the gained results and
taking into consideration existing drafts for
enhanced alert management a concept was drafted
for the specific task of collision avoidance as a first
approach. The concept covers a technical
combination of different sensor information together
with the use of data recorded by VDR systems to
contribute to the reduction of the high number of
alarms and warnings presently observed on board of
The investigations were partly performed under
the framework of a national Research and
Development project funded by the German Ministry
of Transport Building and Urban Affairs, and under
the European MarNIS project, funded by the
European Commission, Department for Energy and
Transport (Willems & Glansdorp, 2006).
2.1 Integrated Navigation Systems
According to the existing IMO Performance
Standards a integrated navigation systems (INS) is
defined as a system that supports safety of
navigation by evaluating inputs from several
independent and different sensors, combining them
to provide information giving timely warnings of
potential dangers and degradation of integrity of this
information. By now three different categories A, B
and C of INS are established. The lowest level INS
category A has as a minimum to provide the
information of position, speed, heading and time,
each clearly marked with an indication of integrity.
The second level category INS (B), is defined as a
system that automatically, continually and
graphically indicates the ship’s position, speed and
heading and, where available, depth in relation to the
planned route as well as to known and detected
hazards. Finally INS(C), is a system that provides
means to automatically control heading, track or
speed and monitor the performance and status of
these controls.
The definitions and categories are under
reviewing presently. One aim of the work of the
IMO Correspondence Group reviewing the standard
is, to elaborate a more generic definition and start
with a totally new functional approach, where tasks
and functions will use as the basis for INS definition.
In future INS will be defined as such, if it performs
at least two of the navigational tasks route
monitoring, collision avoidance and track control. Of
course further navigational tasks may also be
integrated to such systems. Additionally an alert
management system should become a mandatory
part of a future INS and is specified in the draft
standard in a separate chapter.
Table 1. Required mandatory IMO alarms for selected
navigational devices
INS component / Number of mandatory alarms
Heading Control System 3
Track Control System 10
Radar 5
Echo sounder 2
Gyro compass 3
Bridge watch 1
alarm 2
A inventory looking at the required navigational
alerts was performed and the result is summarized in
Table 1.
2.2 Analysis of alarm management
In the frame of different projects a series of several
empirical studies were performed to analyse the
present state. These studies were aimed at the
improvement of ship borne alarm management of
INS. It was started with a review of kind and types
of alarm messages implemented to navigations
systems. Considering the technical integration of the
relative new Automatic Identification System (AIS)
the situation is summarized in the following figure.
It can be seen, that the number of implemented
alarm messages to increases rapidly with the
interconnection to other navigation systems and the
level of integration consequently.
Moreover the example shows, that the number of
real alarm messages implemented to the systems is
much more higher than the number of required
mandatory IMO alarms. The number of potential
alarms and the design of alarm systems in general
seems to be a problem (Earthy, 2006b).
Fig. 1. Number of technical alarm messages implemented to
selected stand alone and connected systems
Further for this purpose real alarm situations on
board of vessels were continuously recorded (e.g.
Lepsoe & Eide, 2005). Interviews and questionnaires
with experts were used additionally to collect data
about operational needs of the navigators (Motz &
Baldauf, 2007).
With respect to kind and frequency of alarms a
great variety was detected. A discussion of the
gained results showed that strong correlations are
indicated in respect to the area related navigational
situations (open sea, coastal area and confined
waters). As one of the main reasons it was found,
that the implemented alarm algorithms are fixed, as,
e.g., collision warnings, having no suitable technical
option to adapt automatically alarming to changing
conditions of a navigational situation. Figure 2
illustrates this result exemplarily.
open sea coastal confined
Navigational situation
Frequency of alarms per hour
Fig. 2. Average frequency of alarms depending on sea areas for
a voyage of a passenger vessel
On the other hand all the studies have also shown
a great dependency of the alarm rates on the specific
navigation devices integrated on the bridges. As can
be seen from the example given in Figure 3 the
majority of alarms were registered at the radar
device and were dangerous target alarms mainly.
Heading control
Track control
Echo Sounder
Gyro Compass
Alarm. Managem. engine.
Bridge alarm system
Fire alarm system
Ballast water display
Frequency of alarms
Fig. 3. Frequency of alarms per device
Basing on the results it has been concluded, that a
future alarm management should harmonize the
operation, handling, distribution and presentation of
alerts. To avoid the uncontrolled increase of alarms,
a set of priorities based on urgency of the required
response is needed to improve the operator’s
situation awareness and his ability to take effective
action. Therefore a new philosophy is suggested for
the prioritization and categorization of alarms. Alert
is defined as umbrella term for the indication of any
abnormal situation with three different priorities of
Alarm (highest priority) - immediate awareness
and action required;
warning - awareness of changed condition;
caution - awareness of condition which does not
warrant an alarm or warning condition, but still
requires attention out of the ordinary
consideration of the situation or of given
The three priorities should be indicated visual and
acoustically in different ways.
To categorize the alerts further, the following two
alert categories are specified at the moment.
navigational alerts - functional indication of
dangerous situation, e.g., collision warning, depth
technical alerts - equipment failure or loss.
Basic concepts for improvement of collision
warnings are already available but has to be further
researched and developed. Investigations should be
dedicated to apply the concept according to a
functional approach for new alarm management.
Finally, the alert management HMI should be
integrated to support the bridge team in the
immediate identification of any abnormal situation,
including the source and reason for the abnormal
situation and in its decisions for the necessary
actions. The alert management HMI should be
provided at least at the position from where the
vessel is navigated and fulfil two major functions:
indicating and identifying alerts, allowing the
acknowledgment of alerts by the bridge team.
2.3 Case study of a real collision scenario
A couple of real situations were investigated to
analyse the present situation regarding the
operational integration of AIS for the purposes of
collision avoidance and to identify potential existing
technical lacks and problems as a basis for better
integration of this new technology into the
navigation process on board. One example of a
collision scenario is used her to highlight some
aspects of integration.
The tracks depicted in Figure 4 belongs to an
example of a scenario happened in open sea area
with a traffic separation scheme during night time
and conditions of good to moderate visibility. Four
vessels (A-D) equipped with AIS were involved in
the situation that led to a collision between target
"B" and "D". These tracks were produced by using
an ECDIS based software on basis of AIS data
recorded with own AIS equipment installed in
laboratory for scientific investigations and operating
in the "listen-mode" only.
Fig. 4. Target tracks reconstructed on basis of recorded AIS
For the purposes of a more detailed statistical
analysis a section of 20 minutes was taken from the
continuous record. The data were modified and
made anonymous before the analysis was started.
The analysis of the available AIS data was
performed with a self created software and numerous
results were gained. The intention of the analysis
was not to identify who is to blame but to highlight
the operation of AIS for further integration of the
system into the process.
The main outcome of this analysis can be
summarised as follows:
Regarding voyage related data:
The destination data of at least one of the
involved target were not correct, because course
data do not correspond with port of destination
The used format for port of destination and ETA
did not comply with the recommendations of the
Regarding the dynamic data:
The heading information of one of the involved
vessels was obviously wrong (great difference
between COG and heading),
The optional AIS information about rate of turn
was not available for major part of the
observation period
Regarding the transmission scheme:
The standards defined by the responsible
organisations require shorter update rates and
transmissions if the ship is manoeuvring.
Although several course changes were registered
from the record, no change in the update rates of
the relevant targets was observed during the
whole tracking period.
Furthermore, a number of duplicated and tripled
messages, probably from repeater stations, were
On one hand the results of this spotlight confirm
the known problems about the reliability respectively
the uncertainty of AIS data. On the other hand it also
emphasises the necessity of great carefulness when
using data of the system for decision making for
collision avoidance. The most important issue that is
illustrated by the given example is that AIS should
never be used as the sole source for decision making.
However, with respect to the potential of
integrated navigation systems the example shows
also, that there is a urgent need for enhanced alarm
management. Obviously no alarm has influenced the
situation awareness of the responsible watch officers
as intended by the IMO rules. From whatever reason
of the officers behaviour that lead to the collision
maybe the dangerous target alarm was not switched
on at all - it is to simple, to categorise the cause of
the accident as a so called very popular "Human
Factor". If that is recognised, then it has at least to be
taken into account, that there were more than one
"human failure". Regarding the alarming it has to be
concluded again, that alarm algorithms has to be
much more enhanced. More effective alarms are
needed in a way that the only occur in condition,
when the operator is really oversee critical
conditions and there is a real need to support and
complete the officers' situation awareness. This is
presently not the case, especially for the dangerous
target alarm algorithms implemented to AIS,
Radar/ARPA and other integrated systems. That is
on reason, way it is allowed to switch of dangerous
target alarms.
3.1 Performance Standards on INS
The existing as well as the reviewed INS
performance standards call for combination of
systems, data and information '... to provide
information giving timely warnings of dangerous
situations …'. As already mentioned above, for that
purpose, three different priorities indicating three
different levels of urgency for taking actions are
suggested. This approach may be also useful for the
enhancement of dangerous target alarms.
As investigations have shown (inter alia by
Baldauf 2006) there is an unsatisfactory exchange of
data and information available on a ship's
navigational bridge from different sensors and
sources. Taking into account the behaviour of
navigators it is clear that alarm thresholds for
dangerous targets are depending on situation
parameters, mainly sea area and visibility but also
own ship's and target's speed and course, sizes,
manoeuvring characteristics and so on. However,
even the simple connection of CPA calculation
considering also information on land masses and
fairways available from ECDIS are not in use until
now. Also the change of manoeuvring characteristics
depending on ships speed or loading conditions is
not yet covered by any dangerous target alarm
implemented to INS.
3.2 Approach to reduce "Dangerous Target"
Enhanced alert management of future INS needs
more combined use of available information also for
triggering dangerous target alarms. For that purpose
a first generic concept is drafted to combine target
information from different sensors and manoeuvring
information that could be triggered by VDR or
alternatively also from ECDIS recordings (see
Fig. 5).
Core element of the approach is a risk model for
situation assessment. It is applied to the IMO's
approach of three priority alerts. It is used as a basis
for approaching to situation dependent triggering of
dangerous target cautions, warnings and alarms as
well. By now it is assumed, that cautions and
warnings may be switched off by an operator,
whereas alarms may not.
The concept of self adaptation of thresholds
contains algorithms respectively options to take into
account and process sea area and visibility
information as well. The manoeuvring information
will then be used for automatic adaptation of the
TCPA related limits of the dangerous target alarms
presently in use.
Fig. 5. Generic concept for use of combined information of INS
to self-adapting and triggering situation dependent dangerous
target alarms
The calculation of the situation dependent
thresholds is considering the real ship dimensions
and the type of encounter situation as well.
3.3 Application of a risk model for situation
Situation assessment is a fundamental basis for
actions to avoid collisions. The main problem until
today is the lack of missing common parameter and
criteria for situation assessment. Hilgert and Baldauf
have already investigated this problem with regard to
the need for “on board” assessment of encounter
situations taking into consideration the aspect of an
existing or developing risk of collision.
The responsible navigational officers have to
ensure that the risk level given as an expression of
the danger of a collision must be kept on an
acceptable level during the entire voyage. Hilgert &
Baldauf (1996) has developed of a COLREGS based
model consisting of four risk levels. These levels are
derived from the actions required by the relevant
steering and sailing rules. For the “on board” use of
the model variable limit values were defined. They
can be calculated and compared with actual
measurement values of CPA and the actual distance
between ships involved in the encounter situation.
An overview on the model is given in following
Table 2. Simplified risk model for situation assessment
risk level
limit values and criteria
Level 1:
risk of
collision is developing
and RNG > R
Level 2:
risk of
collision exists
and R
Level 3:
danger of
collision is developing
and R
Level 4: danger of
collisions exists
and RNG < R
With respect to the IMO's priorities risk level 2
corresponds to caution (situation requires attention
out of ordinary consideration), risk evel 3
corresponds to warning (changed conditions, which
may become hazardous, if no actions is taken) and
risk level 4 to alarm (immediate action is necessary).
The limit values defined for the model have to be
adjusted according to the type of encounter (head
on meeting, overtaking or crossing courses),
visibility (good or restricted) and the dimensions of
the ships involved. C
is the limit value for the
minimum safe passing distance which must be
compared with the actual CPA. Dependent on the
specific situation parameters C
varies between 0,25
nm and 1,5 nm. R
, R
and R
are limit values for
distance borders mainly dependent on the relative
velocity of the approaching vessels and response
time limits for necessary actions to comply with the
rules. These values correspond in general to ARPA
limits of TCPA.
With respect to an encounter situation on crossing
courses under conditions of good visibility the
"assessment range" R
represents that distance from
which the "stand on" vessel has to keep her speed
and course. If the “give way” vessel has not taken
appropriate action up to the "manoeuvring range"
, so the "stand on" vessel may take action in
accordance with rule 17 (a) (ii). The last limit value
represents the "critical range" R
indicates that limit for the "stand on" vessel where
she has to initiate her evasive manoeuvre according
to rule 17 (b) (see following figure).
Fig. 6. Application of the risk model to a encounter situation on
crossing courses under conditions of good visibility
3.4 Use of data recorded by VDR or ECDIS
Recorded manoeuvring data should be used to adapt
the limits in a INS according to the prevailing
circumstances. Therefore the continuous recordings
of integrated systems should be used and relevant
data streams extracted to either a manoeuvring
database or a simulation module that calculates the
necessary manoeuvring parameter on basis of actual
measurements. In this way the thresholds for ranges
, R
, and especially R
) respectively the
corresponding times (especially the time for a course
change of 90° as basis of R