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Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
INCREASING THE SAFETY OF LIFE AT SEA WITH THE HELP OF ADVANCED
TECHNOLOGY
P Pennanen, P Ruponen, H Ramm-Schmidt and D Lindroth, NAPA, Finland
SUMMARY
Flooding of a passenger ship is always a dangerous situation, especially if there is water on a large undivided vehicle
deck of a ferry or RoPax. A decision support system that automatically activates when flooding is detected and provides
status awareness, predictions on the survivability and a timescale of expected flooding progression, is a valuable tool for
the crew onboard the damaged ship. The system needs to present the results in a clear way, enabling the crew to take
informed decisions about evacuation and possible abandonment of the ship. In this paper the key features of a decision
support system for flooding emergencies are presented, with the focus on RoPax specific features, such as accounting for
possible accumulated water on the vehicle deck.
1. INTRODUCTION
Modern RoPax ships offer fast and efficient
transportation services all over the world. The safety of
RoPax ships has evolved throughout the history of
commercial RoPax traffic, but still accidents do happen.
Fires seem to occur quite regularly but fortunately
seldom lead to casualties. Capsizing and sinking on the
other hand are quite rare events, but the characteristic
rapid capsizing of a RoPax ship may lead to large
number of casualties, like in the Herald of Free
Enterprise, the Estonia and the Sewol accidents.
RoPax ships typically operate in dense traffic areas with
tight time schedules and short port turn around times.
They typically carry a small crew in relation to the
number of passengers. Moreover, the weight of the cargo
represents a large share of the total deadweight of the
ship. Therefore, the cargo weight and its CoG (centre of
gravity) may have a considerable effect on the stability
and behaviour of the ship.
In many ways, the structure and damage stability
behaviour of a modern RoPax vessel resembles that of a
modern cruise ship with a dense subdivision under the
bulkhead deck. The RoPax ships do, however, have some
remarkable differences to cruise ships, namely the large
undivided vehicle deck and a possible large lower hold
below the bulkhead deck, Fig. 1. Also possible shifting
of cargo due to excessive heel of the ship, as well as the
large WT doors in bow and stern for easy loading and
discharging, are factors that need to be taken into account
when assessing damage stability characteristics of a
RoPax ship.
The rule development work in respect to passenger ship
operational safety, recently carried out at International
Maritime Organization (IMO), [1], has clearly been more
focused on “pure passenger ships”, i.e. cruise ships, of a
considerable size [2]. The majority of the passenger ships
covered by the rules are, however, smaller ferries and
RoPax vessels.
Figure 1: Important characteristics of a RoPax ship for damage stability and survivability assessment
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
As mentioned, many of the passenger ship rules are
common for cruise ships and RoPax vessels. One of
these is the SOLAS II-1 Regulation 8-1.3 requiring for
provision of operational information to the Master for
safe return to port after a flooding casualty [1].
2. CONCEPT
2.1 REQUIREMENTS
The concept of an integrated decision support system
utilizing existing sensor data for automatically initiated
damage assessment and prediction was introduced by
Pennanen et al. [3]. Based on interviews with experts in
the cruise industry, an integrated decision support system
has the following main requirements:
Ease-of-use
Results presented in a clear and easy-to-
understand form
Online connection to the ship’s tank, flood level
and draft measurement as well as door status
and navigation system
Constant monitoring of the ship’s safety level,
i.e. vulnerability
Constant monitoring of the ship’s flooding level
sensors in order to detect damage
Survivability assessment in the event of
flooding
Flooding prediction and monitoring to enable
efficient countermeasures in an emergency
Based on these requirements, the general system concept
can be described as comprising two distinct modes of
operation:
Vulnerability monitoring for increasing the
safety awareness onboard an intact ship
Survivability assessment and Decision Support
in case of a flooding emergency
This system needs to constantly monitor the vulnerability
of the ship to flooding hazards, based on operational
status, number of open WT doors, etc. Continuous
monitoring of the vulnerability increases the awareness
of the crew about risks related to the current condition.
Another major benefit of the normal vulnerability
monitoring mode is that the crew will become familiar
with the system, and thus possible problems with the
signals from the level sensors and the status of the doors
are immediately recognized.
In case floodwater is detected, the system automatically
presents the flooding extent and severity of the situation.
At the same time the system calculates a prediction for
the survivability of the people on board the ship.
2.2 VESSEL TRIAGE
Vessel TRIAGE is a method for assessing and
communicating the safety status of vessels in maritime
accidents and incidents. The method is intended for use
by both vessels and maritime emergency responders to
assess whether the subject vessel can provide a safe
environment for the people onboard. The details are
presented by Nordström et al. [4]. The method is
currently under consideration for further testing its
adequacy in search and rescue operations by the IMO
Sub-Committee on Navigation, Communication and
Search and Rescue
The method expresses the safety status of the vessel in
terms of a Vessel TRIAGE category. There are four
categories: GREEN, YELLOW, READ and BLACK (see
Table 1). However, the category BLACK is not relevant
for decision support onboard the damaged ship since in
that case the ship has already been lost.
Table 1: Vessel TRIAGE categories [4]
GREEN Vessel is safe and can be assumed to
remain so
YELLOW Vessel is currently safe but there is a
risk that the situation will get worse
RED
Level of safety has significantly
worsened or will worsen and external
actions are required to ensure the safety
of the people aboard
BLACK Vessel is no longer safe and has been
lost
3. USER INTERFACE
In a distress situation, the decision support system should
really support the user, not the other way round. This
means that the required input data from the user must be
minimised. Almost all this data is already available
through sensors serving various systems onboard. All
these signals, provided by the tank gauging, flood level
sensors, machinery automation, navigation system and
the loading computer, can be integrated into the decision
support system.
The calculation of the predicted behaviour of the ship
should be triggered automatically, without need for any
user intervention.
The output of the system must be very clear and
unambiguous, minimizing the need for the user to
perform any detailed interpretation of the calculation
results. The use of simple graphs and colour codes is
preferred, Fig. 2. The Vessel TRIAGE methodology
should be applied to ensure common understanding
between the crew onboard the damaged ship and the
shore-based support, as well as the search and rescue
personnel.
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
Figure 2: Colour code representation of survivability
Due to the difference between cruise ships and RoPax
vessels, all necessary information will not be reliably
available through sensors. Therefore, some vital
information needs to be given by the user. This must also
be made very clear and as easy as possible.
The actual loading condition at the time of the accident
must be used. The online gauge data for the tanks is
easily available, but for RoPax ships the real weight and
center of gravity for the cargo may be difficult to
estimate accurately during the loading. Therefore, a ship
type specific loading computer, with RoRo cargo loading
features, is preferred.
The permeability of the vehicle deck depends on the
loading condition and it is difficult to estimate it visually.
SOLAS II-1 Regulation 7-3 provides two separate values
for permeability of the ro-ro spaces, namely 0.90 for
loaded conditions and 0.95 for unloaded (ballast)
condition. The same can be used also in a decision
support system onboard, and the applied value can be
selected based on the loading condition.
Finally, in collision cases, an approximate location of the
impact is needed for more realistic assessment of
possible accumulation of water on the vehicle deck.
Figure 3: Concept of the user interface, indicating the flooding extent and the predicted survivability level
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
4. CALCULATION METHODS
4.1 FLOODING DETECTION
A crucial requirement for correct assessment of the
survivability level is a fast detection of floodwater.
Therefore, the ship must be equipped with a sufficient
number of well-placed level sensors. Simple on/off
switches are not suitable since it is essential to get
estimation of both the volume of floodwater and the
flooding rate. This issue needs to be considered already
during the design of the ship since retrofit installation of
flooding sensors is both difficult and expensive. Based
on the level sensor data an approximation of the breach
can be done, Ruponen et al. [5].
Flooding detection on the vehicle deck(s) is a technical
challenge since a very large volume of water can still
result in minimal water heights at the sensor locations.
Consequently, a decision support system for flooding
emergency must also allow for manual input, e.g. based
on visual observations. A binary input on whether the
vehicle deck is flooded or not should be enough if the
amount of accumulated water can be approximated e.g.
on the basis of significant wave height.
4.2 FLOODING PREDICTION
On the basis of the current loading condition (fetched
from a vessel type specific, good quality loading
computer) and the detected breaches in the hull, a time-
domain prediction of progressive flooding can be
performed. The status of the doors (open/closed) is also
necessary, especially for the WT doors. In order to
achieve a certain degree of conservativeness, all fire
doors with unknown status are considered to be open.
The flooding predictions are updated at regular intervals,
so that measured floodwater is included in the initial
condition for the next prediction.
The applied calculation method for the time-domain
flooding prediction is a pressure-correction algorithm,
described by Ruponen in [6] and [7]. The method has
been fully validated, also against measurement data from
full-scale flooding tests, [9].
5. SURVIVABILITY ASSESSMENT
5.1 BACKGROUND
The survivability level of the people onboard the
damaged ship is based on both the current situation and
the latest prediction of progressive flooding and the
development of the stability.
Previously, the described decision support system has
been developed especially for cruise ships. The applied
methods for survivability assessment on the basis of the
flooding extent and stability of the damaged ship have
been presented by Ruponen et al. [5].
For ferries and RoPax ships the compartments below the
main vehicle deck are usually very similar to the cruise
ships, and in principle the same methods for prediction of
progressive flooding can be used. However, two separate
stability failure modes have been identified for a
damaged RoPax ship, Tsakalakis et al. [9]:
accumulated water on deck (WoD)
flooding of large lower hold (LLH)
The latter one is related to insufficient reserve buoyancy.
Thus the same treatment of floodwater as in other
compartments below the bulkhead deck should be
enough to provide a correct assessment of the
survivability.
Accumulated water on the vehicle deck requires specific
approach. The revised guidelines on operational
information for masters of passenger ships for safe return
to port (SDC 3/21 Annex 3), [1], in paragraph 27 simply
state that for ro-ro passenger ships: "there should be
algorithms in the software for estimating the effect of
water accumulation on deck (WoD)". In the following
this extremely important issues is discussed and the first
approach to handle it in a decision support system is
presented.
5.2 WATER ON DECK (WoD)
In decision support for flooding emergencies in RoPax
ships, special concern needs to be paid on the water on
deck (WoD) problem. The vehicle deck can be flooded
through a pumping effect of waves if the hull is breached
above the vehicle deck, e.g. due to a collision, Fig. 4. The
European Gateway accident, thoroughly studied by
Spouge [10], is an example of this kind of scenario,
where the vehicle deck was flooded due to a large
transient heeling angle. The vehicle deck can also be
flooded through the bow doors (the Herald of Free
Enterprise and the Estonia accidents), or even by
firefighting water, as described by Krüger et al. [11].
Figure 4: Accumulation of water on vehicle deck due to
the waves in a collision damage
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
Figure 5: Definition of residual freeboard in a collision damage, where the vehicle deck is breached
Considering the past accidents, detected or predicted
water on the main vehicle deck should immediately
trigger the Vessel TRIAGE colour code RED.
For stability calculations the amount of accumulated
water may be approximated with the same approach as in
the so-called Stockholm Agreement (European Union
Directive 2003/25/EC), Fig. 6. However, this requires
some manual user input:
approximated significant wave height
damaged side and approximate longitudinal
extent of the breach to the vehicle deck, Fig. 5
Applying the minimum vertical distance between the
vehicle deck edge and the sea level as the residual
freeboard works as a worst case scenario, and should
ensure conservative results if the breach extents are
unknown.
The calculation procedure for the Stockholm Agreement
is deterministic, thus often considered as non-suitable to
be done together with the probabilistic damage stability
calculations of SOLAS. However, for use onboard a
damaged ship, the deterministic approach is actually very
appropriate.
Recently, also alternative methods for accounting the
water on deck effects has been proposed by Krüger et al.
[11], based on the fact that accumulated water increases
the roll period of the ship.
Figure 6: Height of accumulated water on the vehicle
deck based on residual freeboard and operational
significant wave heights (Hs) for the Stockholm
Agreement
5.3 SURVIVABILITY LEVEL
The Vessel TRIAGE methodology recognizes two
separate threat factors for a damaged ship, [4]:
flooding
listing/stability
The extent of flooding is critical information, and the
severity of the case should be proportional to the size of
the ship. In practice this means that a two compartment
damage is more dangerous for a 100 m RoPax than for a
300 m cruise ship.
The effect of damage stability on the survivability and
safety level can be assessed based on the stability of the
damaged ship. The s-factor in SOLAS II-1 Part II-1 Reg.
7, with proposed changes regarding flooding of ro-ro
spaces, is applied:
4
1
max
max
Trange
range
TGZ
GZ
Ks final (1)
where GZmax is limited to TGZmax and range is limited to
Trange. If the damage case involves a ro-ro space TGZmax
= 0.20 m and Trange = 20°, otherwise TGZmax = 0.12 m
and Trange = 16°. In this context, also the possible large
lower hold (LLH) is considered as a ro-ro space, and if it
is flooded the more stringent requirements are used.
The effect of the heel angle
is accounted with the
coefficient:
715
15
K (2)
when the heeling angle is between 7° and 15°. With
smaller heel angles K = 1 and if the heeling exceeds 15°
then K = 0. This approach is supported by the SOLAS
requirement to be able to lower the lifeboats at a heling
angle up to 15°.
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
The range is limited to the angle, where the first
unprotected opening is immersed. Only real unprotected
openings above the bulkhead deck should be considered
in order to avoid a too conservative approach that would
limit the reserve buoyancy of the hull. On the other hand,
if no limitation of the range is used, the results could be
too optimistic.
The threshold values for the Vessel TRIAGE colour
coding can be defined based on the s-factor, as presented
by Ruponen et al. [5].
5.4 NEXT STEPS
The presented ideas for accounting the flooding of the
vehicle deck in the assessment of the survivability and
safety level still need to be tested with several realistic
damage scenarios. These should also include cases,
where the watertight integrity is not lost but the flooding
of the vehicle deck is caused either by an open/lost bow
door or firefighting water. Based on these tests the final
approach to the problem can then be selected.
6. CONCLUSIONS
In the event of damage leading to flooding, it is essential
that the crew is well aware of the severity of the
situation. This is an important prerequisite for making the
correct decisions.
It is crucial that the relevant information is immediately
available with minimum manual intervention or data
input. Preferably all input should be automatically
available. The relevant status and prediction information
must be presented in an unambiguous way without need
for the user to make further analysis of them. The
flooding extent is a vital part of this information.
Especially the flooding of vehicle decks in a RoPax is
always very dangerous situation.
The presented approach to decision support tool for
flooding emergencies constantly updates the calculations
for the survivability level. Thus e.g. detected flooding to
an undamaged compartment immediately results in
reduced survivability level. This kind of integrated
decision support can solve the over confidentiality bias
of the Captain in an emergency situation. If the damage
really is a minor one, unnecessary evacuation can safely
be avoided. On the other hand, for serious situations the
evacuation and orderly abandonment of the ship can be
started early enough.
Despite of the fact that the presented concept utilizes
advanced calculations with state-of-the-art methods, all
complexity should be hidden from the user. In order to
increase the user’s confidence towards the system,
detailed information is available, for example for training
purposes. Manual input and relevant results, however,
must be kept on a simple and clear level. Application of
Vessel TRIAGE standard colour codes helps in the
decision making and communication much more than
presenting the righting lever (GZ) curves, which requires
user interpretation. This should also be taken into
account in the rule development work and make sure that
the rules do not prevent development of more advanced
systems in the future.
7. REFERENCES
1. IMO SDC 3/21, Report To The Maritime Safety
Committee, Annex 3: Revised Guidelines on
Operational Information for Masters of
Passenger Ships for Safe Return to Port, Feb
2016.
2. HUTCHINSON, K, SCOTT, A. 2015. Current
and possible future intact and damage stability
passenger ship regulations, specifically the
provision of damage stability information and
verification tools to the master, RINA Damaged
Ship III, 25-25 March 2015, London, UK.
3. PENNANEN, P., RUPONEN, P., RAMM-
SCHMIDT, H. 2015. Integrated Decision
Support System for Increased Passenger Ship
Safety, RINA Damaged Ship III, 25-25 March
2015, London, UK.
4. NORDSTRÖM, J., GOERLANDT, F.,
SARSAMA, J., LEPPÄNEN, P., NISSILÄ, M.,
RUPONEN, P., LÜBCKE, T., SONNINEN, S.
2016. Vessel TRIAGE: a method for assessing
and communicating the safety status of vessels
in maritime distress situations, Safety Science,
85:117-129.
5. RUPONEN, P., PENNANEN, P., LINDROTH,
D. 2015. Prediction of Survivability for
Decision Support in Ship Flooding Emergency,
Proceedings of the 12th International
Conference on the Stability of Ships and Ocean
Vehicles, STAB2015, Glasgow, UK, pp. 987-
997.
6. RUPONEN, P. Progressive Flooding of a
Damaged Passenger Ship, TKK Dissertations
94, 2007.
7. RUPONEN, P. 2014. Adaptive Time Step in
Simulation of Progressive Flooding, Ocean
Engineering, Vol. 78, pp. 35-44.
8. RUPONEN, P., KURVINEN, P., SAISTO, I.,
HARRAS, J. Experimental and numerical study
on progressive flooding in full-scale, RINA
Transactions, Vol. 152. pp., A197–A207, 2010.
9. TSAKALAKIS, N., CICHOWICZ, J.,
VASSALOS, D. 2010. In Pursuit of Passenger
Ship Survivability Quantification, Proceedings
Design & Operation of Ferries & Ro-Pax Vessels, 25-26 May 2016, London, UK
© 2016: The Royal Institution of Naval Architects
of the 4th International Maritime Conference on
Design for Safety, 18-20 October 2010, Trieste,
Italy.
10. SPOUGE, J. R. 1986. The Technical
Investigation of the Sinking of the Ro-Ro Ferry
European Gateway, RINA Transactions, Vol.
128, pp. 49-72.
11. KRÜGER, S., NAFOUTI, O., MEINS, C. 2015
A New Approach for the Water On Deck
Problem of RoRo-Passenger Ships, Proceedings
of the 12th International Conference on the
Stability of Ships and Ocean Vehicles
STAB2015, 14-19 June 2015, Glasgow,
Scotland.
8. AUTHORS BIOGRAPHIES
Mr. Petri Pennanen holds the current position of Senior
Adviser at Napa Ltd. He is responsible for regulatory
relations, concentrating on rule development work at
IMO and close co-operation with other regulatory bodies
like classification societies. His previous experience
includes passenger ship design and software applications
used on board ships. During his 19-year career at Napa,
he has been heading loading computer deliveries and
customer support, moving later on to software product
development and research activities in ship stability and
decision support, being finally responsible for the
business related to loading computers and decision
support as a senior product manager.
Dr. Pekka Ruponen holds the current position of Lead
Research Engineer at Napa Ltd. He is responsible for
ship stability and safety related research and
development. His previous experience includes
development and validation of a time-domain flooding
simulation method. He has over ten years of experience
in damage stability calculations and he has authored
several journal articles and conference papers in the field
of ship stability and safety.
Capt. Henrik Ramm-Schmidt holds the current
position of Product Manager – Safety Solutions at Napa
Ltd. He is responsible for product management of
Napa’s Safety Solutions and Loading Computer systems.
During his 5-year career at Napa he has been involved in
Napa’s ship system deliveries, key account activities,
sales and product development. His previous experience
includes active seagoing experience in all positions from
deck hand to Engineer to Master on various ship types
such as tankers, RoRo, HSC and coasters.
Mr. Daniel Lindroth holds the current position of Lead
Technical Consultant at Napa Ltd. He is working as an
expert in stability and regulatory matters concerning both
IMO and class requirements. During his 14-year career at
NAPA he has been working with designers, development
and leading several development projects related to
stability and regulations.
