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1 INTRODUCTION

In the 21st century, the acceleration of global warming

is noticeable. This results in a significant reduction of

ice extent and ice thickness in the Arctic compared to

the conditions prevailing in the 20th century. Lighter

ice conditions result in increased ship traffic in the

Arctic. However, despite the clear trend in reducing

when determining forecast data regarding a

significant time distance, e.g. for the mid and end of

the 21st century [16, 9, 1, 7, 10] . The first reason is to

consider forecasts for various climate change paths

(the most frequently carried out studies are RCP 4.5

and RCP 8.5) [9, 16]. The authors of the publication

confirm that the forecast results presented by

per year. It should therefore be understood that the

possibility of year-round navigation has been

assumed. Meanwhile, the above work [10] based the

above statement on the publication [1], which use

2030 year as a benchmark year, for which assumed

that the NSR will be fully operational all-year round.

But not considered what ice class of ship will be used

presented a map with predicted ranges for ice-free

. Pastusiak

not working for the whole studied period. The studied period of 15 navigation seasons from statistical point of

view is too short period of time to forecast trends and cycles in the near future.

DOI: 10.12716/1001.18.03.

494

the Swedish-Finish ice classes). There are ships that

have a steel hull and that are structurally fit for

navigation in the open sea and that, despite not being

strengthened for navigation in ice, are capable of

navigating in very light ice conditions with their own

are grey ice of 0.15 m thickness [11] or ice conditions

with acceptable Ice Numeral [15] for navigation [2],

following another work [17]. The above work

time window on the NSR, but accepted passage in ice-

free conditions through 80% or 90% of the total NSR

extent only. Assumed this passage will be easily

realized with a minor icebreaker support. The above-

mentioned discrepancies in research methods based

impossible.

The aim of this study is to investigate the number

What are the inter-annual changes in ice cover that

limit navigation for open water, middle and high ice

class ships and are there any relationships between ice

conditions and the movement of these ships?; How

long is the navigable season for particular ice classes

of ships?; Is there a noticeable difference between

individual ice classes, justifying higher costs of

construction and subsequent operation in ice areas

and outside these areas, when navigation on the NSR

is not possible in the winter and spring season.

http://www.nsra.ru, now https://www.nsr.rosatom.ru)

and Center of High North Logistic (http://www.arctic-

lio.com). The following ice maps of the Arctic Ocean

were used: the Arctic Marginal Ice Zone files in vector

ESRI Shapefile format that contain two edge lines, for

ice concentration 18% and 81%, published daily by US

(https://usicecenter.gov/Products/ArchiveSearchMulti

?table=DailyArcticShapefiles&linkChange=arc-two);

the Arctic regional (separate seas) maps in raster GIF

карты Евразийской Арктики); the Arctic regional

during summer time with ice concentration only with

by Arctic and Antarctic Research Institute AARI,

(http://www.old.aari.ru/main.php?lg=0&id=17, the tab

Оперативные данные and Региональные ледовые

карты Евразийской Арктики); the Arctic general

maps of ice concentration or stage of development, in

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for navigation and a very large convergence in closing

of the NSR for navigation (Fig. 1). Rough data and

closing day is easier to predict by about 2 times than

the opening and closing dates of the NSR for transit

shipping for 18% and 81% indicates an extension of

the navigable season for Arc4 and Arc5 class ships.

Approximation of trend lines with polynominal

for concentrations 18% and 81% are similar only in

recent years. i.e. since navigation season 2017 (yellow

arrow lines) presented on Figure 3.

Figure 1. Opening and closing time for navigation for

Figure 2. Convergent extremes for opening day of the

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Western Part of the NSR

Next, analysis of rough data for 81% concentration

showed consistency in between length of navigable

season (Fig. 5) at Western Part of the NSR and length

of navigable season for entire NSR in 60% cases (black

ellipses). Rough data for 81% concentration for

Eastern Part of the NSR (magenta diamants) shows

higher length of navigable season for about 40 days in

relation to Western Part and the whole NSR. Lines of

rough data for the Western Part of the NSR and the

Analyse of length of navigable season for both ice

concentrations 18% and 81% (Fig. 6) found in 30%

cases good consistency of extremes (black arrow lines)

and in 15% cases clear inconsistency (magenta arrow

lines). Cycle of ice phenomena was equal 4-5 years. It

was related mainly to the Western Part of the NSR.

Based on the graphs, it is not possible to establish a

phenomena of the NSR for transit navigation for 18%

and 81% of ice concentration edges. It seems that the

factors.

Figure 6. Seasonal consistency and inconsistency of length

3.2 Length of navigation season of Arc4 and Arc5 based

on ships’ traffic

The length of navigable season for Arc4 and Arc5

class ships received from ships’ traffic during summer

navigation seasons 2012, 2013, 2015, 2017 and 2021.

Only for these seasons satisfactory complete statistical

calendar.

The length of 50% of Arc5-class ships voyages was

year). It follows that the time window for ships of ice

For both ice classes Arc4 and Arc5 the rule was

days with light navigation conditions) in a given

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received from ships’ traffic during summer navigation

seasons 2012, 2013, 2015, 2017 and 2021. Only for these

could be obtained. Statistical analysis of ships’ traffic

showed that the length of 50% of Arc7-class ships

voyages was inside of 120 days an average [3], from

day 248 till day 367 Julian calendar (2nd day in a new

calendar year). The maximal navigable time window

calendar year).

Five nuclear-powered icebreakers were available

to escort ships in difficult ice conditions. There were:

Arktika, 50 let Pobedy, Sibir, Vaygach, Taimyr and

icebreaker can escort one ship of the Arc7, Arc5 or

Sea Route in the winter season. Next, the question

was asked: If the voyage time depends on the speed of

days. In December, from 31 to 37 days.

days from 7 to 28 days.

period in relation to average passage time. This was in

made in the summer season, when ships with lower

3.4 The speed limitation for ice class Arc7 ships

Now we try to reply to the second question: What

navigating alone or with help of an icebreaker. Most

appropriate were data form summer navigation

season 2021. In first approach obtained the simplified

3-dimensional diagram of speed reached by Arc7

ships with R-square 0.28 (Fig. 7). Found the speed

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one-year-old ice), but with partial Ca coverage only

30%. The greatest partial coverage of the sea region

within the red range on the permissible speed chart

Arc7 class ships, independent year-round navigation

is allowed only in the southwestern part of the Kara

of the Northern Sea Route [6]. And there, the most

severe ice navigation conditions considered concern

independently in hard ice conditions only from July 1

to November 30. Navigation with icebreaker support

is unlimited in terms of season and ice conditions. The

changes are summarized in the Tables 1 and 2.

other table thick

first-year ice

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summer/autumn summer/autumn

________________________________________________

assistance and denied

second-year ice assistance and denied

independent

navigation in hard ice

navigation conditions

[6]

ice thickness limit) independent

navigation in hard ice

[13] NOT included [6]

________________________________________________

4.2 Research results and Russian ice navigation

regulations

At the beginning, the question was asked why the

limit of ice thickness established in the study is 120

cm, while navigation in first-year (average) ice with a

thickness in the range of 70-120 cm is acceptable, i.e.

methods for two regions at latitudes 84.2° and 71.6°

for 70 m x 70 m spatial resolution [20] showed

identical results. The average value increased by one

standard deviation was 147% of the average value, the

(accepted in maritime navigation) was 194% of the

average value and the highest value was 261% of the

average. The value reduced by one standard deviation

Russian regulations. However, the limit value of

120cm increased by double standard deviation is

233cm and this is more than the value permitted by

the regulations of the Russian Federation. Therefore, it

navigable and non-navigable ice thickness are in

Maritime Register of Shipping [13, 14] and Rules for

navigation in the waters of the Northern Sea Route

and used to determine the partial fractions limiting

fraction of ice with a thickness smaller than the

thickness than the maximal Sa usually reached values

of 20% but could decrease even to 10%.

It should be assumed that the limit values of ice

conditions come down to the average thickness of the

ice with a smaller thickness than the maximal usually

reached values of 20%, but could reach 10% only and

usually was of an average thickness of Sb and Sc up to

45cm, but in extreme cases up to 56cm. This means

cm (thin first-year ice) and in extreme cases even ice

with a thickness of 70-120 cm (medium first-year ice)

with a partial fraction Cb of 10% only. The thinnest

partial fraction of ice Sc could have a thickness of 5 -

Based on the analysis of ice maps, it was determined

navigated in ice with an equivalent thickness of up to

with a thickness of 45.3 cm or more (maximal 50cm).

waters of the Northern Sea Route [6]. The time of

changing these regulations coincided with the export

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average thickness not exceeding 95 cm and a

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window of 1 to 90 days, an average of 33 days. The

maximal navigable time window of Arc4-class ships

was from 209 till 300 day of the Julian calendar, in a

time window of 16 to 86 days, an average of 75 days.

The maximal navigable time window of Arc5-class

ships was from 196 till 315 day of the Julian calendar

using the most powerful Arc7-class cargo ships does