29
1 INTRODUCTION
The FSCIR A1 ice class ships are designed to navigate
in non-Arctic waters. However, they may operate in
polar waters under specified ice conditions. For the
purposes of voyage planning, the average speed
achieved over the entire route, i.e. operating speed, is
important. It takes into account the time a ship is
underway, the time waiting for ice and weather
conditions to improve, downtime resulting from the
need to wait for an icebreaker to arrive, the time
required to form a convoy and similar additional
delays. However, for the purpose of direct guidance of
a ship in ice, the safe technical on-scene speed must be
taken into account. To determine whether the ship
generally is able to enter specific ice conditions some
administrative traffic control systems have been
implemented such as the old and modern Northern Sea
Route Administration Rules of navigation on the NSR,
Canadian AIRSS or IMO POLARIS. They advise
mariners weather may enter the area or it is not
allowed or may enter under certain limitation. Above
decision systems are organized in different manner
and do not take into account all aspects of navigation
in ice and in areas of extremely low temperatures. The
aim of this work is an attempt to link various
dependencies of the above systems and guidelines for
construction of ships for navigation in ice and in
extremely low ambient temperature.
History and Development of Risk Assessment for
Navigation in Ice may be divided in two directions.
First one is related Risk Assessment and limitation of
movement included in local regulations like Russian
NSR (older, simple), Canadian AIRSS, Russian NSR
(modern, developed) and IMO POLARIS. They are
related to local specific area, ship ice class, ice
concentration, ice thickness and other ice forms or
state. Second one includes Manuals for Navigation in
Ice like Ice Passport [40] (basic parameters of safe
movement), Ice Passport with various adds and Polar
Water Operational Manual. They are related to ship’s
speed, ice class, ice concentration, ice thickness and
other ice forms or state. Guidelines for the
Development of a Polar Water Operational Manual are
related to icebreaking capabilities (ability to pass ice).
Information on ice conditions in which ship can make
progress may be drawn from numerical analysis,
model test or ice trials. It may include information on
ice strength for new or decayed ice and of snow cover.
Limitations of Navigation by the FSCIR Ice Class A1 Ship
in Polar Waters
T. Pastusiak
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: The FSCIR A1 ice class ships are designed to navigate in non-Arctic waters, but they may operate in
polar waters under specified ice conditions. This work took into consideration speed and ice conditions limiting
movement of the ship in ice during independent voyage and with icebreaker escort. Same time, the safety of the
ship was analysed, taking into account the ship's draft, so that the restrictions resulting from the width of the hull
ice strengthening belt and the possibility of damage to the propeller were met.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 20
Number 1
March 2026
DOI: 10.12716/1001.20.01.04
30
Canadian Arctic Ice Regime Shipping System uses
numerical analysis Risk assessment and limitation of
ship movement including ship ice class, ice
concentration, ice thickness and other ice forms or state
using Ice Multiplyer and finally Ice Numeral. Same
time the work of McCallum [27] used ice trials (statistic
accidents and incidents of ships in ice). By this way
received relationships between Ice Numeral, safe
speed limit and unsafe speed limit for ship ice class, ice
concentration, ice thickness and other ice forms or
state. These results will be used in this work.
2 LITERATURE REVIEW
A review of the literature on ship movement in ice
showed that in the years 1938–1990 the principles of
ship navigation in ice were analysed on-scene [18] and
the first generalizations were determined [52, 4, 49, 33,
34, 16, 23, 1, 10, 11, 42, 35, 2, 7]. In the years 1965-2013,
the dependence of ship speed on various forms of the
ice cover was studied [9, 41, 40, 2, 25, 29, 14, 3, 44, 22,
15, 21]. The problem has not been fully resolved until
modern times [31, 32]. Most of these publications
described technical speed. It is technical speed that the
ship's commander needs when making decisions on-
scene.
Administrative traffic control systems improve
navigation safety in polar regions. They provide ship
captains with information on which routes and speeds
to safely navigate in ice-covered areas. However, it
should be taken into account that the fundamental
(paramount) principle of safe and at the same time
economical operation of ships in ice areas is the
assessment of limitations in available data, limitations
regarding correlations in between ship speed and ice
concentration and thickness, the concept of how to
avoid an ice and, if not possible, how to find the easiest
track though ice. Additionally, there have been voices
that no systematic feedback is currently available to
help ship operators and crew related to the use of these
administrative traffic regulation systems [24, 5].
Individual regulations related to the construction of
ships destined for ice or polar navigation and
administrative methods of risk assessment and traffic
regulation were reviewed. A general convergence in
solving the problem was observed. At the same time, it
was observed that individual regulations do not
provide a comprehensive solution.
The Canadian AIRSS decision-making system
includes detailed division of seas into regions, the
ship's ice or polar class, ice conditions, and navigation
type (independent or with icebreaker assistance). The
decision-making system takes into account normal ice
conditions and lighter ice conditions (decayed ice,
thaw holes, or rotten ice), as well as heavier ice
conditions (roughness, deformation of ice).
Ships with a steel hull without reinforcements for
navigation in ice (Canadian E ice class) can operate in
Open Water (ice concentration less than 10%), Bergy
Water (ice of land origin present with sea ice in
concentrations less than 10% [50]), Brash Ice (ice
fragments of horizontal dimension up to 2 meters),
New Ice, Nilas and Ice Rind (up to 10 cm thick) and
Grey Ice (up to 15 cm thick). There are very light ice
conditions. FSCIR A1 ice class ships are allowed to
navigate in heavier ice conditions, i.e., thin first-year
ice up to 70 cm thick [47]. These ice conditions
constitute the basic criterion for safe navigation in
normal ice conditions. Taking into account the above
limitations, the ice overpassing capability of an FSCIR
A1 ice class ship under the Canadian Arctic Ice Regime
Shipping System is presented in Table 1 [47].
Table 1. Ice Multiplyer (IM) – normal ice conditions for
FSCIR 1A ice class ship. Asterix means no direct equivalent
to the POLARIS scale of ice conditions.
Ice Class
Ice-Free
New Ice
Grey Ice
Grey White Ice
Thin First Year ice 1st Stage
Thin First Year Ice 2nd Stage
Medium First Year ice
less than 1 m thick
Medium First Year Ice
Thick First Year Ice
Second Year Ice
Light Multi Year Ice,
less than 2.5 m thick
Heavy Multi Year Ice
1A
2
2
2
1
1
1
-1*
-1
-2
-4
-4
-4*
Ice Multiplyer presented in Table 1 may be a little
changed for ice decay and ice roughness. In case ice is
decayed, it means multiyear ice (that can be more than
300 cm thick), second year ice (that can be more than
250 cm thick), thick first year (that can be more than
120 cm thick) or medium first year ice (that can be up
to 120 cm thick) [47, 28, 50]has Thaw Holes or is Rotten,
the value of 1 may be added to the Ice Multiplyer forth
an ice type. In case an ice is rough, it means total ice
concentration is 60% or greater and more than one-
third of an ice type is deformed, the value of 1 should
be substracted from Ice Multiplyer for the rough ice
[47, 28]. It should be noted, that trace of old ice (ice
concentration lower than 10 %) is not required to be
part of the Ice Numeral calculation. But in case a trace
of Old Ice is found, caution should be exercised when
navigating [28, 48].
The construction requirements for FSCIR ice class
1A ship is a minimum speed of 5 knots in channels with
brash ice, i.e. channels of already broken ice [26, 46].
Need to mention the term Brash Ice means ice pieces of
horizontal dimension up to 2 meters. For FSCIR ice
class 1A ship has additional limitation of ice thickness
0.8 m [26, 8, 46, 36]. This ship may need to navigate
with the icebreaker assistance when necessary [26] but
is not allowed to ice ramming. The term ramming
means the ship is stopped, move backwards and then
ram into the ice again, and in that way move forward
through the ice [26].
Next, FSCIR classification do not give direct
equivalency of other registry. Need to mention Finnish
– Swedish 1A ice class can be equivalent of Russian
Maritime Register of Shipping Arc4/LU4 1/LU3 Class
or IMO POLAR Class PC6 - ICE IA /E3 in case fulfill
main engine propulsion power standards of the proper
register rules [26].
In case the ship fulfill all Arc4/LU4 construction
rules requirements she is allowed to navigate during
summer/autumn period of time in the Arctic in open
31
floating first-year ice up to 0.8 meters thickness that
may include old ice inclusions. In harder ice conditions
during winter/spring period of time this ship may
navigate in the Arctic in open floating (up to total
concentration 60%) first-year ice up to 0.6 meters
thickness. This ship is allowed also for year-round
navigation in freezing non-arctic seas in light ice
conditions [39, 26]. The “light ice conditions” in the
Northern Sea Route Administration web site [37] mean
miscellaneous ice thickness up to total concentration
up to 30%. Thickness of ice is not given directly. The
partial components of the above contain first year
medium ice of thickness 0.7-1.2 meters, first year thick
ice of thickness 1.2 meters, residual ice of thickness
range 0.3-1.8 meters and old ice of thickness at least 3.0
meters [50, 12, 39]. However, in another place it is
specified that Finnish – Swedish 1A ice class ship that
do not fulfill main engine propulsion power standards,
may be accepted as the lower Ice3/LU3 RMRS ice class.
This ice class allow to make regular voyage in open
floating ice cake of non-arctic seas up to 0.7 meters
thick [39, 26]. It means Ice3/LU3 RMRS ice class ship
(100 A1 ICE Class 1B) is allowed navigate in non-artic
seas in ice up to 0.7 meters thickness, total
concentration up to 60% and horizontal size of a floe
up to 20 meters [39, 26] or in thin first year ice in Arctic
seas up to 0.5 meters thickness [47]. Irrespective of the
above mentioned rules should be emphasized the ship
in service will not follow Classification Rules for ice
navigation assessment but will follow Ice Passport (Ice
Certificate) [38]. Possibility of operation of a ship in
particular area is determined depending on the season,
current weather conditions, actual ice conditions and
presence of icebreaker assistance. The decision is
responsibility of the ship operator [39, 20, 24].
The IMO-approved POLARIS method [20] takes
into account the ship's ice class, ice conditions and type
of navigation (independent or with assistance of
icebreaker). Additionally, it distinguishes between
normal ice conditions and decayed ice (decayed ice,
thaw holes or rotten ice). The ship's captain is given
greater decision-making independence. He or she
should consider not only information available on
charts and ice bulletins, but also on-scene information
based on observations of ice conditions directly from
the ship. The ability of a ship classified as FSCIR A1 ice
class to overpass maximal ice parameters according to
the Polar Water Risk Assessment POLARIS
recommended by IMO [20] (taking into account the
above limitations) is presented in Table 2.
The RIO presented in Table 2 may be a little
changed for ice decay during times of higher ambient
temperatures for certain ice types. But this lighter
requirements for decayed ice are related to Medium
First Year ice less than 1 m thick, Medium First Year Ice
(that can be up to 120 cm thick)and Thick First Year Ice
(that can be more than 120 cm thick) only [47, 28, 50].
In case the ice cover has Thaw Holes or is Rotten, the
ship should use another RIV table for decayed ice [20].
In this case the RIV value is reduced by 1 only. No
special table for heavier ice navigation condition like
deformed ice is used inside the POLARIS system.
Comparing the Ice Multiplyer IM variability (Table
1) with the Risk Index Value RIV variability (Table 2),
it was noted that the absolute RIV values for a Class 1A
FSCIR ship increase more rapidly with distance from
the safe navigation limit. In both the Canadian AIRSS
and IMO POLARIS systems, the limit of safe
navigation for normal ice conditions is Thin First Year
Ice of Stage 2. The IMO POLARIS system assumes a
lower value, i.e., zero, when the AIRSS assumes a more
gentle IM value of 1.
Table 2. Risk Index Values – normal ice conditions [20].
Ice Class
Ice-Free
New Ice
Grey Ice
Grey White Ice
Thin First Year ice 1st Stage
Thin First Year Ice 2nd Stage
Medium First Year ice
less than 1 m thick
Medium First Year Ice
Thick First Year Ice
Second Year Ice
Light Multi Year Ice,
less than
2.5 m thick
Heavy Multi Year Ice
1A
3
2
2
2
1
0
-1
-2
-3
-4
-5
-5
For voyage planning purposes when icebreaker
escort is intended to be used, the RIO derived from
non-escorted historical ice data may be assumed to be
modified by adding 10 to its calculated value [20].
However, it is cautioned that this is an average value
which can vary significantly. For on-scene operations,
the RIO for ship under escort should be determined
taking into consideration the ice immediately ahead of
this ship. In case the icebreaker has a smaller beam than
the escorted ship, any unmodified ice out to the
maximum beam of the escorted ship should be
assumed as that actual ice regime. In practice it means
the safe speed of a ship reduced greatly.
In case of identified elevated operational risk, more
caution should be used and a speed reduction is
recommended [20]. This outcome is only applicable to
ice classes PC 1 to PC 7, but not for low ice classes nor
for no ice strengthened ships. These lower ice classes
ships should do not enter in the ice regime with
negative value of RIO. It means other alternative route
should be planned. Other alternative is employment of
an icebreaker to mitigate the risk.
The above data indicate the following restrictions
for the operation of the FSCIR A1 ship in ice: maximal
total concentration up to 60%, open water of total
concentration below 10% where no limitations are
considered in case the ship is able to avoid contact with
ice of thicker then allowed by the ice class, 80 cm
thickness limit due to ice strengthening hull
construction and during summer/autumn period of
time in the Arctic / Antarctic polar regions. The ice
taken into consideration may include old ice
inclusions. The term “inclusion” should be assumed as
ice of total concentration below 10%. The ship should
avoid contact with these old ice inclusions. During
icebreaker escort IM/RIV values may be increased by
adding 10. In addition, this lighter ice conditions under
consideration should be limited to Medium First Year
ice less than 1 m thick, Medium First Year Ice (that can
be up to 120 cm thick) and Thick First Year Ice (that can
be more than 120 cm thick) only.
32
The first Russian Northern Sea Route
Administration Rules were a decision-making system
that included a general division of seas into regions
(halves of the sea), a ship's ice or polar class, ice
conditions, and a type of navigation (independent or
with icebreaker assistance). The decision-making
system was inherently very general. The contemporary
decision-making system in force on the Northern Sea
Route is very similar to the Canadian AIRSS. It includes
a general division of seas into regions (halves of the
sea), a detailed division of seas into regions, a ship's ice
or polar class, ice conditions, and a type of navigation
(independent or with assistance of icebreaker).
The Russian Ice Passport, later approved by the
IMO and incorporated into the Polar Water
Operational Manual, could also be considered a system
for regulating ship movement in ice. It consists of two
general parts. The first considers the safe speed of a
ship during independent navigation. The second
provides recommendations for sailing with an
icebreaker escort. Both take into account the various ice
conditions a ship may encounter along its route.
3 RESEARCH METHODOLOGY
The paper compiles various recommendations and
studies regarding ship speed and existing ice
conditions. The relationship between safe ship speed
and total ice concentration and thickness (stage of
development) was examined. Ice decay and roughness
were also considered. The paper utilized research
results that established the relationship between safe
and unsafe ship speeds determined using the AIRSS Ice
Numeral [27]. Therefore, the Canadian AIRSS risk
assessment served as the basis for further
investigation. The literature [43] identified the use of
ship speed results related to AIRSS data [27] for tables
related to RIO [20]. This was assumed to be an incorrect
connection of input data for the analysis.
First, the Ice Multiplier data for FCIR 1A ice class
ship navigating in polar waters was extracted from the
table. In next step calculated Ice Numeral for ice
thickness and total ice concentration. Results presented
in Table 1. Green cells give Ice Numeral IN values not
lower than zero. It means in these ice regime conditions
navigation of this ship is allowed. Red cells give IN
values below zero. It means in these ice regime
conditions navigation of this ship is denied.
In next step values of Ice Numeral presented in
Table 1 substituted with safe speed of FSCIR 1A ice
class ship (Polar Category B) navigating in polar waters
presented in Table 2. In this way, a table of the
dependence of the ship's safe speed on ice thickness
and total ice concentration was obtained. Green cells
give maximum safe speed values. Red cells do not
contain speed value as there are ice conditions that do
not ensure safe navigation.
Based on the data in Table 3, we created charts of
the FSCIR A1 ship's speed depending on total ice
concentration. The area under the ice thickness curve
at a given value defines the safe ship speed range for
given ice navigation conditions, as presented in the Ice
Certificate (Ice Passport) [6]. The analysis was
performed for normal ice conditions and decayed ice
conditions.
For the resulting raw charts, boundary lines were
added. These result from legal regulations and
scientific research discussed during the Literature
Review (Chapter 2).
4 RESULTS AND DISCUSSION
4.1 Limitations related to independent navigation
Values of Ice Numeral IN for normal ice conditions for
FSCIR 1A ice class ship navigating in polar waters
according to AIRSS [28] presented in Table 3. Green
cells indicate in what conditions navigation is allowed.
Red cells determine under what conditions navigation
is not allowed (denied).
Table 3. Risk Index Values – normal ice conditions [20].
Description
Ice
thickness
Hi [cm]
Ice total concentration CT [%]
10
20
30
40
50
60
70
80
90
100
ice free
0
20
new ice
10
20
20
20
20
20
20
20
20
20
20
grey ice
15
20
20
20
20
20
20
20
20
20
20
grey white
30
19
18
17
16
15
14
13
12
11
10
thin FY 1st stage
50
19
18
17
16
15
14
13
12
11
10
thin FY 2nd stage
70
19
18
17
16
15
14
13
12
11
10
medium FY 1st
stage
95
17
14
11
8
5
2
-1
-4
-7
-10
thick FY
120
16
12
8
4
0
-4
-8
-12
-16
-20
2ndY
250
14
8
2
-4
-10
-16
-22
-28
-34
-40
MY
300
14
8
2
-4
-10
-16
-22
-28
-34
-40
Table 4 compares the Ice Numeral values [47] with
the maximum permissible safe speeds [27, 51, 43] and
the RIO values [20] corresponding to the speeds for Ice
Numeral. The obtained values result directly from the
Stage of Development and ship's ice class in both
documents mentioned. The RIO ranges overlap.
Therefore, it is not possible to clearly determine the
safe speed based on RIO by directly assigning RIO
values to individual table cells [20]. Taking the above
into account, it was decided to conduct further research
based on the Ice Multiplyer and Ice Numeral values
determined using the AIRSS method [47].
Table 4. Safe speed for FSCIR 1A ice class ship (Polar
Category B) navigating in polar waters. Made by the Author
following Canadian AIRSS [47, 27, 51, 43] and IMO [20].
IN (AIRSS)
SPEED [knots]
RIO (POLARIS)
<0
0
(+)2 – (-) 50
0-8
4
6-16
9-13
5
0-23
14-15
6
12-25
16
7
18-26
17
8
21-27
18
9
24-28
19
10
27-29
20
11
30-20
Table 5 specifies the speed values for normal ice
conditions for FSCIR A1 ice class ships navigating in
polar waters according to [47]. Green cells indicate the
conditions under which navigation is allowed. Red
cells indicate the conditions under which navigation is
not allowed (denied).
33
Table 5. Values of ship’s speed in ice for normal ice
conditions for FSCIR 1A ice class ship (Polar Category B)
navigating in polar waters according to [47, 27, 51, 43].
Stage of
Development
Thickn
ess of
ice Hi
[cm]
Ice total concentration CT [%]
10
20
30
40
50
60
70
80
90
100
ice free
0
11
new ice
10
11
11
11
11
11
11
11
11
11
11
grey ice
15
11
11
11
11
11
11
11
11
11
11
grey white
30
10
9
8
7
6
6
5
5
5
5
thin FY 1st
stage
50
10
9
8
7
6
6
5
5
5
5
thin FY 2nd
stage
70
10
9
8
7
6
6
5
5
5
5
medium FY 1st
stage
95
8
6
5
4
4
4
thick FY
120
7
5
4
4
2ndY
250
6
4
4
MY
300
6
4
4
It was noted that a ship with ice class A1 can
navigate brash ice up to 0.8 meters thick [26]. The
definition of "brash ice" according to [50] specifies a
floe diameter of 2 meters. The weight of such a block of
sea ice, after converting its dimensions, is
approximately 2.58 tons. For comparison purposes, the
equivalent horizontal size of a floe was calculated for
the weight of 2.58 tons in relation to the thickness of a
floe.
Results presented on Figure 1. It should be noted
that a block of ice with a diameter close to its thickness
(1.5 meters in this case) will be unstable and may rotate.
This may increase the horizontal size of the ice floe at
the expense of reducing its thickness. This is why the
first limit on the permissible vertical dimensions of the
ice floe was established (thickness of ice floe above 1.5
meters). Next and binding limitation was introduced
due to ice thickness limitation of the ice strengthened
hull of FSCIR A1 ice class ship equal 0.8 meters. It gives
allowable range of ice floe dimensions (green area).
Every ship with steel hull may navigate in New Ice,
Nilas, ice rinds and pancake ice up to thickness of 10
centimetres [19, 17, 35, 50, 47]. This creates a
conditional (for Fresh Ice) expansion of the horizontal
dimensions of ice below 10 centimetres of ice thickness
(yellow area).
Figure 1. Equivalent horizontal size of a floe for the weight
2.58 tons and allowable limits for ice navigation.
A ship with ice class 1A can navigate in brash ice up
to 0.8 meters thick [26]. The definition of "brash ice"
according to [50] is a diameter of 2 meters. The FSCIR
1A ice class ships (as equivalency of Arc4/LU4/IMO
POLAR class PC6-ICE 1A /E3) may navigate in open
floating (concentration up to 60%) first year ice up to
0.8 meters height, if engine power fulfil requirements
for this ice class [26]. Precisely, during
summer/autumn navigation in the Arctic the ship may
perform voyage in open floating (up to total
concentration 60%) first-year ice up to 0.8 m thickness.
But during winter/spring navigation in the Arctic
(Antarctic) may perform voyage in open floating (up to
total concentration 60%) first-year ice up to 0.6-m
thickness only and, if engine power fulfil requirements
for this ice class.
Based on the above restrictions, an FSCIR 1A class
ship that meets the propulsion engine power
requirements for the Arc4/LU4/IMO POLAR class PC6-
ICE 1A/E3 may navigate during the summer/autumn
period in the Arctic (Antarctic) area in open pack ice
(total concentration up to 60%), first-year ice up to 0.8
meters thick and limited to no more than brash ice
(maximum horizontal dimension of 2 meters). When a
mixed Stage of Development composition up to 30% of
total ice concentration occurs, the ship may navigate in
areas with first-year medium ice of 0.7-1.2 meters
(average 0.95 meters) thickness and/or residual ice of
0.3-1.8 meters thickness with inclusions of old ice
exceeding 3.0 meters thick. However, it should be
assumed that navigation in the area of existence of ice
with thickness above 0.8 meters with the help of
experienced deck crew (master, chef officer and OOW)
will come down to avoiding ice clusters with a
thickness exceeding 0.8 meters. Above limitations are
related to normal ice conditions, i.e. not decayed ice.
Next, based on the ship's speed in ice for normal ice
conditions for an FSCIR A1 ice class ship (Polar
Category B) navigating in polar waters, a chart of
maximum ship speeds in ice (Figure 2) was created
(Figure 2) under normal ice conditions. The absolute
limit is open pack ice (maximum 60% of total ice
concentration) for ice thicknesses not exceeding 0.8
meters. In the case of thicker ice (average 95 cm and 120
cm), the limit will be a total ice concentration not
exceeding 30%. Both the average 95 cm and 120 cm ice
thickness exceed permissible values due to the width
of the ship's reinforced hull. Therefore, it should be
assumed that these ice thicknesses only apply to
inclusions (ice concentration below 10%), and the ship
will be able to detect and effectively avoid these
inclusions – while maintaining an additionally reduced
speed (Figure 2). It should also be assumed that ice
thicknesses exceeding 1.5 meters (i.e. 250 cm) cannot be
taken into consideration due to maximal thickness and
horizontal dimension of floe of maximal weight equal
2.58 tons (see explanation to Figure 1).
34
Figure 2. Safe speed in normal ice conditions.
Next, the above procedure was applied to ship's
speed in ice values for decayed ice and rough ice
conditions for an FSCIR A1 ice class ship (Polar
Category B) navigating in polar waters. The obtained
graphs showed maximum ship speeds in ice related to
total ice concentration and thickness of decayed ice
(Figure 3) and rough ice (Figure 4). It should be
emphasized that in both cases, decayed and rough ice
navigation conditions (regimes) the additional
limitations are same like for normal ice navigation
conditions (regime).
Figure 3. Safe speed in decayed ice.
Figure 4. Safe speed in rough ice.
4.2 Limitations related to icebreaker escort used
Following results of works on operational safe speed of
escorted FSCIR A1 class ship [13] the diagrams of
maximal safe speed and safe distance to an icebreaker
making escort operations in various ice navigation
conditions (regimes) was made. They were related to
total ice concentration, level ice thickness, ice
compression or ridged ice thickness. Ice thickness
above 0.8 meters is not a limitation when using an
icebreaker escort. However, this is provided that the
escorted ship on its way in the channel behind the
icebreaker does not encounter ice conditions exceeding
its capabilities for independent navigation. It should
therefore be recalled that when proceeding behind an
icebreaker, the ice regime criterion is based on the ice
conditions encountered in front of the escorted ship,
i.e. in the channel behind the icebreaker [20]. If the
icebreaker has a width smaller than the ship, then the
criterion for ice regime is the ice not modified by the
icebreaker within the width of the escorted ship [20].
Statistical results [13] show that in the operating
intervals presented in these graphs total ice
concentration and thickness of ice are not limiting
escorted ship of FSCIR 1A ice class to follow icebreaker
when an escorted ship encounters ice not modified by
icebreaker. Also, as a general rule can be adopted the
following: as higher speed as higher distance to
icebreaker and as harder ice conditions as lower
distance to icebreaker. In average, distance 2.5 cables to
icebreaker is required for speed of 9.5-10.8 knots.
4.3 Limitations related to hull ice strengthened belt
The maximum and minimum ice class draughts at fore,
amidships and aft perpendiculars shall be followed
during ship operation in ice. Details should be found
in the Classification Certificate. Reinforced hull belt
extends beyond the UIWL and LIWL limits. The
draught and trim, limited by UIWL, must not be
exceeded. Salinity of sea water along the intended
route should be taken into consideration when loading
a ship. Same way a ship should always be loaded down
at least to the LIWL [30] and no more than till UIWL
(Figure 5). In case ballast tank is situated above the
LIWL and a ship need to be loaded to this water line,
this tank should have devices to prevent the water
from freezing.
Figure 5. Safe drafts Fore and Aft during navigation in ice
infested area; UIWL – Upper Ice Water Line, LIWL – Lower
Ice Water Line, a – ice reinforced belt of hull, b – vertical
distance between UIWL and LIWL.
4.4 Limitations related to vertical clearance of propeller
tip to the lover part of ice floe
So far, limitations resulting from the structural strength
of the hull, the ship's speed, and the ability of the
escorted ship to stop before the icebreaker ahead have
been considered. In addition to the above, additional
limitations resulting from the possibility of propeller
damage must be considered. The ship's draft and the
clearance of the top of the propeller from the lower
edge of floating ice and separate floe must be taken into
account.
35
A propeller clearance, it means a stern frame
clearance, and an ice clearance must be ample enough
to avoid collision between propeller and ice. Stern
frame clearance (Figure 6) is required to avoid ice floes
being forced between the stern frame and the propeller.
The ship's crew has no influence on the amount of a
stern frame clearance. Ice clearance in between level ice
and propeller (Figure 6) is required when there is a risk
that the propeller will hit large floes when the ship is
submerged at the stern at LIWL. This is the worst case
possible. Damage to a ship is most probable when a
ship is going astern. A stern frame clearance should be
at least 0.5 m and the ice clearance should be positive,
it means lower part of level ice (ice floe) should do not
reach propeller tip [45].
Figure 6. Ice clearance at LIWL and stern frame clearance [6,
45].
Requirements related to ice clearance for ship
escorted by icebreaker in polar waters are much higher.
An escorted ship should ensure such stern immersion
that the propeller upper tip will be submerged not less
than double of ice thickness [6]. It means, vertical
clearance between lower part of level ice (ice floe) and
propeller tip should be as high as double thickness of
ice floe (see sample calculations on Figure 7). Above
indicate Russian Polar Rules set higher requirements
for higher ice thickness and FSICR Baltic Rules set
higher requirements for lower ice thickness. This is
consistent with the expected ice thickness in the
navigation areas mentioned. A smaller immersion does
not guarantee protection of propeller from intense
interaction with ice and same way from damages. It
should be emphasized the most dangerous situation is
when a ship operates with a small draft (in ballast
condition or with small amount of cargo). In this case
it is advisable to change the trim by re-ballasting.
Figure 7. Minimal safe stern draught related to floating ice
thickness.
5 CONCLUSIONS
The paper presents ship speed limitations in ice
depending on the concentration and thickness of ice
during independent navigation, speed and distance to
icebreaker in the case of escorted navigation, as well as
ship draft limitations taking into account the location
of the reinforced ice belt of the ship hull and stern draft
limitations taking into account the thickness of ice and
the distance of the level ice floe to the propeller tip.
It should be emphasized, the ice conditions being
analysed in this works are related to clearly defined
thickness of ice, in most cases to level ice. There are rare
conditions in reality. During the ice sheet's accretion
period, a uniform layer of ice (level ice) forms. Under
the influence of wind, ocean currents, or tidal currents,
this uniform layer of ice (level ice) moves. If uniformly
thick, undeformed ice (level ice) encounters an obstacle
in the form of land, shallow water, or slower-moving
ice, compaction begins, which leads to increased ice
concentration and/or stresses that can lead to ice
deformation. Depending on the magnitude and
duration of the pressure process, rafting occurs,
followed by ridge and hummocking of the ice floe.
Consequently, the ice thickness in such areas increases
significantly. Because most of the ice height is below
the water surface, changes in ice thickness indicate
relatively small changes in the ice height above the
water surface. On-scene assessment of ice thickness is
complicated by the overlying snow layer. An
experienced navigator is then necessary to recognize
the locations of rafted, ridged and hummocked ice in
between-level ice among the unevenly lying snow.
Then, above calculations are intended to serve
mariners as a guidance only. No part of this work is
intended to exempt from obligation to exercise
mariners due diligence, and proper use own
knowledge, professional experience and good
seamanship.
Then . . . irrespective to any calculations and
statistics the most important for safe Ice Navigation is
HUMAN FACTOR. While ship is navigating in
difficult ice conditions, safe achievement of voyage
objective depends on EXPERIENCE and GOODWILL
of Captain, Officers On Watch and Helmsmen, and
COOPERATION of deck crew and engine crew
together.
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