ISO/TR 9814:2025

Technical
Report
ISO/TR 9814
First edition
Ships and marine technology —
2025-06
Good practices of preventing
capsizing during turning of ships
with large profile height
Navires et technologie maritime — Bonnes pratiques de
prévention du chavirement lors du virage des navires à grande
hauteur de profil
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Analysis of capsize accidents of five ships . 3
5.1 General .3
5.2 Ship categories based on cargo space requirements .4
5.2.1 Weight carrier .4
5.2.2 Volume carrier .4
5.2.3 Area carrier .4
5.3 Analysis of capsize accidents .4
5.3.1 General .4
5.3.2 Similarities.4
5.3.3 Differences .5
6 Effect of KG on the GZ curve . 5
6.1 KG and its role in capsizing accidents .5
6.2 Characteristics of hull form and GZ curves .9
6.2.1 General .9
6.2.2 Hull forms with two inflection points along the GZ curve .9
7 Three good practices to prevent capsizing during turning of ships .10
7.1 General .10
7.2 Semi-automatic inclining tests before loaded departure .10
7.2.1 General .10
7.2.2 Features of inclining test before departure .11
7.2.3 Stability screening without inclining test . 12
7.3 Maximum heeling angle while turning .14
7.3.1 General .14
7.3.2 Maritime autonomous surface ships . 15
7.3.3 Considerations on cargo slippage.16
7.4 Precise calculation of free surface moment (FSM) .17
7.4.1 Slack limit of NAPA software .17
7.4.2 FSM at 98 % filling level .17
7.4.3 Improvement of stability calculation software .18
Annex A (informative) Cases of capsizing accidents . 19
Annex B (informative) Additional information on ship features .28
Bibliography .30

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document is prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee SC
8, Ship design.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
There are many similarities between the following ship accidents: the Golden Ray in 2019, the Hoegh Osaka
in 2015, the Sewol ferry in 2014, the Crown Princess in 2006 and the Queen Hind in 2019. By comparing
and analysing the causes of these five accidents, identifying similarities between them, and generalizing the
findings, this document aims to help prevent similar accidents from occurring in the future.
Based on the analysis of the five ship accidents and a similar land truck accident, this document describes
three good practices to prevent similar accidents from recurring. Since similar accidents can occur not only
in old ships but also in the new ships, additional measures are described, as similar accidents can occur
again unless these points are corrected.

v
Technical Report ISO/TR 9814:2025(en)
Ships and marine technology — Good practices of preventing
capsizing during turning of ships with large profile height
1 Scope
This document gives good practices on how to prevent the capsizing of ships with large profile height during
turning.
The following are covered this document:
a) ship turning, centrifugal force, and consequent heeling;
b) accident use cases of capsizing during turning;
c) effect of the KG on the ship stability;
d) three good practices of preventing capsizing during turning of ships.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
capsize
to (cause a boat or ship to) turn upside down by accident while on water
3.2
fishtailing
to cause the tail of an aircraft or the back of a motor car to swing from side to side
3.3
free surface effect
mechanism which can cause a watercraft to become unstable and capsize (3.1)
Note 1 to entry: It refers to the tendency of liquids to move in response to changes in the attitude of a craft's cargo
holds or liquid tanks.
3.4
inclining test
test performed on a ship to determine its stability, lightship weight and the coordinates of its centre of gravity

3.5
integrated monitoring, alarm, and control system
IMACS
computer-based system used for monitoring and controlling various processes in industries such as oil and
gas, power generation, water treatment, and manufacturing
3.6
maritime autonomous surface ship
MASS
increased automation on board ships, which could ultimately reach full autonomy or become a remotely
controlled unmanned vessel
3.7
overturn
single-vehicle accident event in which the vehicle rolls at least 90°
[SOURCE: ISO 6813:1998, 3.2.1, modified — note 1 to entry has been removed.]
3.8
profile height
distance from the waterline to the high point on the ship's structure or cargo, such as a stack of containers
or superstructure which continues more than about 70 % of the ship length
Note 1 to entry: This term is distinct from "air draft", which refers to the height used to assess whether a vessel can
pass beneath a bridge. In contrast, profile height is introduced in this document to specify the height influencing the
vessel's stability. While related to the wind pressure area (3.10), profile height represents a different concept.
3.9
weigh station
facility near a road where vehicles, especially large trucks, can be weighed
3.10
wind pressure area
total area of the ship's exposed surfaces that are subject to wind pressure
3.11
KG
vertical distance (along the ship's centreline) between the keel (K) and the centre of gravity (G)
4 Abbreviated terms
BWT ballast water tank
CCTV closed-circuit television
DWT deadweight
FSM free surface moment
GM metacentric height
GT gross tonnage
GZ stability arm
IMACS integrated monitoring, alarm, and control system
ISC international code on intact stability
KG vertical centre of gravity
kn knot
KST Korean Standard Time
MARIN Maritime Research Institute Netherlands
MASS maritime autonomous surface ship
MSC Maritime Safety Committee
PCTC pure car and truck carrier
SOG speed over the ground
SOLAS International Convention for the Safety of Life At Sea
USCG US Coast Guard
UMSC US Coast Guard Marine Safety Center
5 Analysis of capsize accidents of five ships
5.1 General
Ships can be distinguished by the type and amount of cargo they carry, which has a significant impact on the
shape and stability of the hull of each ship. These ship categories are:
a) weight carrier;
b) volume carrier;
c) area carrier.
In general, ships carrying cargoes heavier than water have a margin of stability. On the other hand, ships
carrying cargoes lighter than water need to secure more volume or deck area to increase revenue. This
requires increasing the structure above the water, which is likely to reduce stability.
The stability of the ship varies across these categories, and ship types have evolved to produce these
differences in stability owing to differences in cargo-carrying efficiency and thus income. The ship types of
volume carriers and area carriers generally tend to have a large profile height.
Ship operation is based on revenue, which is determined by the amount of cargo that the ship can transport.
To increase revenue, ship types such as PCTC have evolved to have a large profile height. The safety of the
ship is closely related to the revenue of ship operations.
NOTE It is similar to the reason why weigh stations are operated for land trucks. The maximum weight that can
be loaded onto the truck is displayed, and drivers are well aware of the changes in vehicle safety according to the
weight and loading of the cargo. Many drivers drive illegally to earn more money. Ships are in a similar situation, and
safety is generally closely linked to economic efficiency, ship designers are expected to consider this reality to ensure
the safety of ships.
This document is about ships that have stability problems even in calm waters. These are area carriers and
some volume carriers. Area carriers are a relatively new type of ship, so greater attention to detail can help
to address their stability weakness.
Ship capsizing is a problem related to dynamic stability while the ship turns and the centrifugal force
generates a heeling moment. For a detailed analysis of five ship capsizing incidents involving large profile
heights, see Annex A. For information on ship features, see Annex B.

5.2 Ship categories based on cargo space requirements
5.2.1 Weight carrier
For heavy-duty cargo ships, such as bulk carriers (e.g. iron ore, coal) and crude oil carriers, the deadweight
(DWT) is an important indicator of profitability. These types of ships generally have a margin of stability.
5.2.2 Volume carrier
In cargo ships that carry lighter (porous) items, such as container ships and general cargo ships, the volume
or gross tonnage (GT) of the hull is an important indicator of profitability. These types of ships are generally
likely to lack stability because the number of floors above the waterline increases to secure space. Among
these types of ships, many ships are observed to have a large profile height.
5.2.3 Area carrier
For ships that require a large parking lot or living area, such as car carriers or cruise ships, the deck area
is an important indicator of income. Since this type of vessel increases the number of floors, it is generally
likely to have a large profile height and therefore lack stability.
5.3 Analysis of capsize accidents
5.3.1 General
Table 1 compares the major parameters of the five ship accidents. The similarities and differences in these
accidents are summarized in 5.3.2 and 5.3.3.
Table 1 — Comparison of five ship accidents
Golden Ray Hoegh Osaka MV Sewol Crown Princess Queen Hind
Year of accident 2019 2015 2014 2006 2019
1994, Japan, 1980, Japan,
Year and location of imported and imported and
2017, Mipo, Korea 2000, Japan 2006, Italy
construction modified 2013 in modified 2017 in
Korea Romania
About 39,4 m About 32,4 m About 21,6 m About 50,7 m About 13,1 m
Profile height
(3,7 times of design (3,2 times of (3,5 times of (5,8 times of (2,08 times of
(above waterline)
draft) design draft) design draft) accident draft) design draft
Draft (design) 10,6 m 10,15 m 6,2 m 8,74 m (accident) 6,30 m
34 609 tons (at acci- 16 886 tons
Displacement 9 750 tons unknown unknown
dent) (DWT)
GT 71 000 tons 51 770 tons 6 800 tons 113 561 tons 3 785 tons
Lack of stability Lack of stability Officer’s incor-
Lack of stability while Lack of stability
while turning while turning rect wheel com-
Cause of accident turning (13,3 kn at while towing
(12 kn at 10 rud- (18 kn at 5 rud- mands (20 kn at
20 rudder angle) and wheel (4 kn)
der angle) der angle) 30 rudder angle)
Metacentric height
0,45 m 0,7 m 0,3 m to 0,5 m
(GM)
NOTE  1 kn = 1,852 km/h.
5.3.2 Similarities
Common observations among the capsize accidents listed in Table 1 can be drawn, including:
— a vessel type with a hull structure that rises high above the waterline (large profile height) generally has
marginal stability;
— in a state of marginal stability, while turning at a fairly high speed in a narrow waterway, a ship can
capsize because it cannot withstand the outward heeling moment caused by the centrifugal force (see
also Figure B.1 and Figure B.2).
As shown in Figure B.2, the centrifugal force is affected by the ship's speed and turning radius, and is more
affected by the speed. Table 1 shows the ship's speed and rudder angle at the time of the accidents. A ship
withstands the heeling moment due to the centrifugal force according to the stability performance of the ship.
5.3.3 Differences
A number of differences can be observed among the capsize accidents listed in Table 1, including the
following.
— The Golden Ray was a ship built by the Mipo shipyard of Korea in 2017, and a lot of data about the accident
situation are left in the electronic recording devices.
— Since the Sewol ferry was an old ship, there were no electronic equipment such as a black box, so there
are few accident records. Therefore, it was difficult to re-generate the accident data using other data
sources.
— The Hoegh Osaka was a ship built in Japan and the shipowner was from Singapore.
— The locations of the accidents: the accident of Hoegh Osaka occurred in England, the Golden Ray's
occurred in the United States, the Sewol ferry accident was in Korea and the Crown Princess accident
was in the United States.
6 Effect of KG on the GZ curve
6.1 KG and its role in capsizing accidents
Figure 1 shows a comparison of the standard stability arm (GZ) curve for normal shipping conditions and
Figure 2 shows the stability arm curve at the time of the accident voyage. The curves were derived by USCG's
Marine Safety Center (UMSC) based on the analysis of the Golden Ray accident. The appearance of the GZ
curve is unusual with two inflection points, and it can be seen that the KG (vertical centre of gravity) was
quite high at the time of the accident (see Figure 2).

Key
S GZ expressed in meters
θ heeling angle, expressed in degrees
1 GM
2 the GZ curve for normal shipping conditions on the Golden Ray
Figure 1 — Normal pure car and truck carrier (PCTC)
Key
S GZ expressed in meters
θ heeling angle, expressed in degrees
1 GM
2 the GZ curve at the Golden Ray accident
Figure 2 — Pure car and truck carrier with accident

[1]
The Golden Ray accident report summarizes the causes of the accident as follows.
— The chief officer made an error when entering ballast quantities into the stability calculation program,
which was identified as the probable cause of the capsizing.
— The number of vehicles on board increased by 94, and the cargo weight increased by approximately
373 tons after the ship entered Brunswick.
— Insufficient righting arm was available to counter the heeling forces generated during the turn, resulting
in the ship overturning due to a lack of restoring force to counteract the heeling moment.
[1]
Figure 3 shows the GZ curve at the time of the Golden Ray accident. The design loading conditions have
been approved by the ship classification society. These design loading conditions show GZ curves in various
loading conditions and are safe voyage conditions. The GZ curve of the accident voyage is insufficient
compared to the designed conditions. Especially when the heeling angle exceeds about 12°, the heeling angle
becomes 45° without an additional heeling moment.
Key
S GZ, expressed in meters
ϕ heel angle, expressed in degrees
1 benchmark loading conditions
2 capsize voyage (heel to port)
3 capsize voyage (heel to starboard)
SOURCE: Based on Reference [1].
Figure 3 — GZ curve at the time of the Golden Ray accident
[16]
In the report by Brooks Bell, who participated in the Sewol ferry investigation, the following is noted.
— As a result of the modifications, the Sewol ferry's cargo-carrying capacity was reduced from 1 450 tons
to 987 tons. The Korean register of shipping also required that the ferry maintain a minimum water
ballast of 1 703 tons.
— At the time of the accident, 476 people were on board, including 443 passengers and 33 crew members.
The joint investigation team reported that the Sewol ferry was carrying approximately 2 142,7 tons of
cargo at the time of the incident.

[21]
Figure 4 shows the GZ curve at the time of the Sewol ferry accident. The KG value, one of the important
parameters determining stability, had gradually increased from the initial estimated value, and the values
reported in subsequent reports.
[15] [20]
Looking at the joint investigation office report in 2014, hull investigation committee report in 2018,
[21]
and the report of the social disasters commission in 2022, the amount of cargo shipped gradually
increased, and the KG value also increased.
Key
S GZ expressed in meters
θ heeling angle, expressed in degrees
1 GM
2 the GZ curve at the Sewol ferry accident
3 GM = 3,306 m, at 1 rad (1 rad = 52,295 9 degrees)
SOURCE: Reproduced with permission from Reference [21].
Figure 4 — GZ curve at the time of Sewol Ferry accident
[20]
Figure 5 shows the other GZ curve at the Sewol ferry accident situation. The GZ value is shown, and the
middle part of the GZ curve is concave like the Golden Ray shown in Figure 3.

Key
S GZ, expressed in meters
ϕ heel angle, expressed in degrees
1 GM
2 the other GZ curve at the Sewol ferry accident
SOURCE: Reproduced with permission from Reference [20].
Figure 5 — The other GZ curve at the time of Sewol Ferry accident
In general, when the ship's centre of gravity, KG, rises, the entire GZ curve, which represents stability of
the ship, rotates clockwise. Figure 3 and Figure 4 show similar cases. Therefore, in many ships, when KG
exceeds the threshold, the righting arm becomes negative, leading to a steep heel and capsizing accident.
6.2 Characteristics of hull form and GZ curves
6.2.1 General
The reason why the GZ curve of the PCTC is unusual (with two inflection points) is explained as follows.
A hull form design is carried out so that the initial GM is large. It is advantageous to be designed so that the ship
is less rocky or tilted during the loading process of car or truck. When the design is carried out for this purpose,
the hull form design usually shows a V-shape near the waterline, and the block coefficient (CB) is small.
In this hull form, at a small heeling angle, the heeling angle is less compared to the external force (heeling
moment), so the crew can mistake it for a safe ship. In addition, due to efforts to maintain the total area
under the GZ curve required by safety regulations, a tendency is observed that the middle part of the GZ
curve becomes concave.
In this hull form, when the heeling moment exceeds the threshold, it quickly tilts to a large heeling angle. For
this reason, PCTCs can have similar accidents in the future, even with new vessels such as the Golden Ray.
6.2.2 Hull forms with two inflection points along the GZ curve
In the case of PCTC or passenger ferry, the GZ curve is unusual with two inflection points. In other words,
the middle portion of the GZ curve is concave. See Figure 2, Figure 3, Figure 4, Figure 5 and Figure A.5.

When the heeling angle exceeds about 12° for Golden Ray, the heeling angle becomes 45° without an
additional heeling moment.
In these types of vessels, the 15° heel angle, where cargo slip begins, is addressed to prevent secondary
large-scale heeling.
7 Three good practices to prevent capsizing during turning of ships
7.1 General
Based on the comparative analysis of the capsize accidents of the five ships described (see 5.3 and Annex A),
7.2 to 7.4 describes methods which can help to improve safety and thus help prevent the recurrence of
similar accidents.
7.2 Semi-automatic inclining tests before loaded departure
7.2.1 General
The first good practice of how to prevent capsizing is performing inclining tests before loaded departure.
[13]
The inclining test is a method to determine the centre of gravity of a ship in lightweight condition. As
shown in Figure 6, the centre of gravity is calculated using the heeling moment generated by moving a
known weight (w) by a known distance (l) and the measured angle of heel at this time.
The inclining test is performed after the completion of a new ship's construction at the shipyard. In most
cases, this test is only performed once or twice in the lifetime of the vessel. By expanding the scope of
application of this technology, applying it to a ship loaded with cargo, and checking the centre of gravity or
KG at every departure, the safe navigation of the ship can be further improved. In particular, it can apply it to
ships that are likely to lack stability, such as car carriers or others with high profile height.
Key
M metacentre
w weight
l distance the weight was moved from its original position
g centre of gravity
g' shifted centre of gravity during heeling
waterline
L
w
shifted waterline during heeling
L ′
w
K keel
baseline
L
b
Figure 6 — Inclining test
7.2.2 Features of inclining test before departure
7.2.2.1 Benefit of accurate KG value
If the accurate KG value of the ship is available, this data can have various benefits including:
— accurate estimation of stability performance;
— safety of the ship can be secured;
— streamlining cargo loading planning;
— saving fuel by improving the voyage efficiency;
— optimization of navigation routes and reduction of navigation time by improving prediction of
manoeuvring performance and motion seaworthiness performance.
With the current method of estimating KG value based on the calculation of the cargo weights, errors due
to frequent arrivals and departures of the ship are accumulated, resulting in increased uncertainty and
reduced operational efficiency.
Data such as the ballast tank water level measured by integrated monitoring, alarm, and control system
®1)
(IMACS ) can automatically be transmitted to the stability calculation computer (LOADCOM) to quickly
perform inclining tests.
IMACS is a sophisticated system that integrates various functions such as data acquisition, data analysis,
process control, and alarm management into a single platform.
7.2.2.2 Accuracy of inclining test before loaded departure
If the inclining test is performed with the cargo loaded condition just before departure, the measurement of
the centre of gravity or KG makes the confirmation of the stability performance (GM and GZ curves) more
accurate and cross checks with the calculation by LOADCOM. It is possible to double check the stability with
the calculation results using the traditional cargo loading report.
The inclination test can be performed without gusty wind or uniformly varying wind and/or current, but
the port is not always so calm when the ship must leave the port.
In particular, for a ship with a high windage profile, a change in the heel angle caused by a slight change in
the wind over time deteriorates the accuracy of the inclining test.
The accuracy of the inclining test before loaded departure cannot be high because there are many cases
where ships depart under bad weather conditions rather than the wind or current conditions performed at
shipyards. However, with the recent development of electronic equipment (IMACS etc.), the level of accuracy
can be improved. ®
1) IMACS is the trademark of a product supplied by Noris Inc. This information is given for the convenience of users of
this document and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if
they can be shown to lead to the same results.

In particular, in order to increase the accuracy of the inclining test in the presence of disturbance, it can be
useful to utilize the image stabilization function used in smartphone photography. For example, the action
®2)
mode on iPhone 14 .
The current inclining test, as one of the procedures for checking the contract requirement between the
shipbuilder and the ship owner, requires a high level of accuracy. However, the proposed inclining test
during ship operation is intended to check safety level, and can be meaningful at a lower accuracy level than
the inclining test performed by shipyards. It can play a sufficient role in screening the safety of departure
(see also 7.2.3).
As the construction and operation of ships with large profile heights is expected to increase in the future,
and the pressure on ship operating schedule is expected to increase, it is possible that there will be a need to
amend IMO regulations.
Discrepancies between the computer calculation (LOADCOM) and the experimental (incline test) results
can occur in many experimental cases. These discrepancies can be overcome through the know-how gained
from the experience of science and technology. A technique that has been developed for a long time can be
used to reduce the difference between the two to a reasonable or tolerable level. When checking if a road
truck is overloaded, it is common practice to rely on measurements rather than calculations.
7.2.2.3 Schedule delay
Inclining tests can be performed just before departure while the vessel is fully loaded with cargo. The
purpose is to double check the vessel’s actual condition versus the computer-generated stability calculations.
This can impact the vessel’s operating schedule.
In fact, checking the weight and centre of gravity of each of 20 000 containers is a complex and time-
consuming task. To increase the accuracy level of that cargo data, more time and money can be required
compared to an inclining test.
The time required to perform an inclining test at a shipyard usually takes about 3 hours. With the help
of electronic devices such as IMACS, the inclining test time can be reduced to 20 minutes. In particular, if
stability-related equipment is installed on modern ships such as the Golden Ray case, inclining tests can be
performed semi-automatically in a short time.
Inclining tests can be performed on existing ships, but in old ships that do not have new equipment such as
IMACS installed, the time required for the inclining test can increase.
7.2.3 Stability screening without inclining test
7.2.3.1 General
When a ship departs from port, multiple steering manoeuvres are employed, including zigzag operations.
Extending these manoeuvres slightly can create an effect similar to that of a turning test, potentially
eliminating the need for an inclining test and reducing departure time delays. For example, using the vessel's
rolling period can yield results comparable to a free roll decay test by leveraging the ship's roll induced by
steering.
In the case of a car, "the handle is light (fishtailing)" corresponds to a case where the KG of a ship is high. It
will be possible to quantify this scientifically. ®
2) iPhone14 is the trademark of a product supplied by Apple Inc. This information is given for the convenience of
users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products may
be used if they can be shown to lead to the same results.

[24]
The GM of a ship can be estimated by means of rolling period. The period of roll and the stability index
[25]
GM can be estimated from Formula (1).
2π ()ak+
T = (1)
gM
GM
where
Τ is the period of roll;
a is the added radius of gyration (added roll moment of inertia);
κ is the radius of gyration (roll moment of inertia) about the longitudinal axis through
the centre of gravity;
g
is the gravitational acceleration;
M is the mean of GM.
GM
Since the radius of gyrations ( a , κ) are obtained during the sea trial for typical loading conditions,
interpolation will be possible for the value of a specific operating condition. In addition, additional
corrections will be possible by utilizing sensor data available in IMACS at the time of departure.
7.2.3.2 Measurement rather than calculation
To calculate the stability of a ship in operation, the weight and position of each cargo are checked using a
document called the loading plan that determines the loading condition. Additionally, the weight and position
of fuel oil, fresh water, ballast water, etc. are entered into the stability calculation computer (LOADCOM).
Then the total weight and centre of gravity or KG of the ship are calculated, and the GZ curve is calculated
based on these values.
Similar to land-based cargo transportation, there are economic and business environments that intentionally
overload the current method of relying solely on cargo stowage calculations for the safety of ships, which is
inherently risky.
The current stowage calculation method is a method in which it is difficult to increase the accuracy. It is
nearly impossible to secure the weight and centre of gravity of all cargo at the same high level. In the case of
land transportation, an overload checkpoint (weigh station) is operated.
Consider a truck carrying 1 000 small parcels. Based on the weight of individual parcels and their loaded
location data, the centre of gravity of the entire cargo can be calculated. On the one hand, it is possible
to measure the centre of gravity of the truck and cargo using weighing devices. Comparing the two, the
idea that relies on measurement will give more stable and accurate results than the method that relies on
calculation.
In land trucks, a weigh station is in operation that checks the weight of trucks running on the road. A similar
regulation can be introduced because ships suffer greater and more serious losses from capsize accidents
than trucks.
In order to increase the accuracy of the current cargo calculation method, it is possible to check the weight
and centre of gravity of all cargo arriving at the port by measuring the weight twice. However, if this is done,
more cost and time delay are expected.
However, as in the case of the Golden Ray, the Hoegh Osaka, and the Sewol ferry, accidents can occur due to
inaccurate calculations of KG or GZ. Also, as in the case of overloaded trucks on a road, intentional violation
is possible, for convenience or economic reasons.

7.2.3.3 In-service inclining test systems
The 2 000 Germanischer Lloyd (GL) regulations have a separate regulation for inclination tests during ship
[22]
operations.
[23]
The American Bureau of Shipping (ABS) has regulations for in-service inclining test for offshore plants.
Methods from those services can be utilized to minimize the delay of the ship schedule.
3)
The online GM monitoring system (OGMS) of Totem-Plus® is a commercial example of utilizing IMACS
signals to automate the in-service inclining test. The system has been in operation for about 20 years on
approximately 100 PCTCs and large container ships.
The measured heeling angle for a known weight and transfer together with the actual displacement (measured
by the draft sensors) allow to measure GM. Figure 7 shows an example of the user interface of OGMS.
Figure 7 — Example of user interface of OGMS
[1]
The inclining experiment by the OGMS can take about 20 minutes. The PCTC Golden Ray at the port of
Brunswick, GA had a functioning OGMS but failed to operate it before sailing, as can be seen in the NTSB report.
7.3 Maximum heeling angle while turning
7.3.1 General
The second good practice of how to prevent capsizing is to maintain a maximum heeling angle while turning.
3) The online GM monitoring system (OGMS) of Totem-Plus® is an example of a suitable product available commercially.
This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of
the product named. Equivalent products may be used if they can be shown to lead to the same results.

The International Code on Intact Stability (IS Code), adopted by the IMO in December 2008 through
[4]–[8]
resolution MSC.267 (85), contains one rule only for passenger ships. The rule provides formulae for
estimating the heeling moment due to turning of a passenger ship and ensuring that this value does not
exceed certain criteria.
7.3.2 Maritime autonomous surface ships
7.3.2.1 General
As the heeling angle changes sensitively to the turning speed during turning, it is difficult to generalize
calculation formulae or computer simulations. Furthermore, as the heeling angle relies heavily on
experiments while turning, it is not easy to apply the rule directly in the practice.
If maritime autonomous surface ships (MASS) become widespread, the way human crews navigate using
their eyes and experience will be different. Since turning is performed using computer controls, regulations
such as limiting the maximum angle of heeling can be checked using this technology.
The reason to limit the heeling angle by 15° is based on the fact that at a heeling angle of 18°, the cargo
loaded without safety devices begins to slide.
For existing ships in operation, the idea of limiting the maximum heeling angle can be applied by extending
the existing idea. Currently, a righting arm curve is created for the heeling moment due to side winds.
Similarly, righting arm curves can be prepared for a combination of heeling moments due to the centrifugal
force generated during turning (see also Figure A.5).
The righting arm curve with the heeling moment can be prepared for each cargo loading condition. If
righting arm curves are prepared for a combination of turning speed and turning radius, navigation is
possible within the maximum allowed range of heeling angle.
7.3.2.2 Proposal by MARIN in the Netherlands
Figure 8 shows the maximum heeling angle and the number of occurrences during turns for various
[7]
passenger ships of 100 m or longer based on the database of MARIN. It shows a fairly diverse distribution,
and a considerable number of cases show heeling angles exceeding 21°, which is the angle at which cargo
[7]
with poor securing is believed to be moving.
In ships that have room for stability and are not expected to have stability problem about cargo overload,
a heeling angle of more than 18° can occur in rough seas. In particular, in the case of sailing yachts, it is
necessary to perform missions even in rough seas and with large heeling angles.
For cargo ships navigating in calm weather, relaxed regulations are applied as relieving cargo restraints
enhances convenience or economy. Therefore, when a large-angle heeling occurs due to a ship's turning in a
calm sea, it is usually due to lack of stability or high turning speed. If the heeling angle exceeds 18° with the
cargo restraints relaxed, movement of unsecured cargo can have fatal consequences for the vessel.

Key
occurrence, expressed in per cen
...