Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

A study of full-scale measurement of channel widening by IB Polaris
Hanyang Gong, Riikka MatalaAker Arctic Technology Inc.
Helsinki, Finlandcomplex management by considering many factors, such as available
icebreakers and operation costs. Such a wide channel could also beopened by one icebreaker. For example, icebreakers could utilizereamers to widen a channel by changing ballast conditions. However,implementing reamers on an icebreaker requires more structural design
and building cost; additionally, the effect of reamers on channel
widening may not be significant. Instead of adding reamers on the ship,
actively using the azimuth propulsion system could be a more
economical and flexible for safe and efficient operations in icy waters.
By customizing the icebreaker’s speed, azimuth thruster turning angles
and propulsion power, the channel can be widened in a prevailing icecondition. For the reader’s interest, solutions of opening channels otherthan using icebreakers do exist. Tugboat operated in freshwaters, such as
Lake Saimaa (the largest freshwater lake in Finland) and the Saimaa
Canal, can break freshwater ice during the winter season by connecting
a detachable icebreaking bow (Aker Arctic, 2018).

ABSTRACT
Escorting merchant ships sometimes requires icebreakers to widen
channels in ice-covered waters. To better understand the icebreaker’s
channel widening capability, this paper presents full-scale tests of theIcebreaker (IB) Polaris in the Bay of Bothnia during 2021 and analyses
the relation between measured channel widths and icebreaker’s
operations, those being: combinations of advancing speeds and two stern
azimuth thrusters’ toe-in angles. The tests showed that operating IBPolaris ahead at a low speed with toe-in angles could open a widechannel in level ice. Such an operation could also widen a previously
opened own channel more. This paper also provides an approach todigitally measuring channel widths from drone videos.

KEY WORDS: Icebreaker; channel widening; winter navigation; icemanagement; full-scale test.

Icebreaker’s capability of widening the channel by its azimuth
propulsion system has been studied earlier. Riska et al. (2015)
documented the full-scale performance of MSV Fennica and MSV
Botnica and presented a semi-empirical method to calculate the channel
width from the pod angles and ship’s speed. The most recent work by
Taimuri et al. (2018) summarised the Aker Arctic-led full-scale tests onchannel widening by icebreaker (IB) Polaris and concluded that thewater flow activated by the azimuth propulsion system could widen thechannel. Continuing their work, this paper presents new full-scale testsof IB Polaris conducted during March 2021 to understand theicebreaker’s channel widening capability further. This paper alsopresents a new approach to digitally measuring the channel width fromcontinuous videos recorded by a drone.

INTRODUCTION
Safe and effective shipping in ice-covered waters requires a reliable
winter navigation system. In the northern Baltic Sea area, the Finnish–
Swedish winter navigation system governs maritime transportation in
winter conditions, ensuring merchant vessels safely reach ports(Goerlandt et al., 2017). Icebreaker assistance as one component of thewinter navigation system provides icebreaking service for merchantships. Icebreakers can escort a merchant ship and lead a convoy by
opening a channel for the assisted ships to travel in brash ice channelconditions. If the assisted merchant ship’s beam is wider than theicebreaker’s, the channel opened by the icebreaker may not be wide
enough for the assisted ship. The surrounding level ice may result insignificant resistance to the assisted ship, causing potential risks ofcollision with other following ships. Therefore, channel widening as anice management option is required in such circumstances.

FULL-SCALE TESTS AND TEST MATRIXA series of full-scale tests on channel widening was performed in theBay of Bothnia on 12~13 March 2021. The studied icebreaker was a 24m-wide IB Polaris (Fig. 1), conceptually designed by Aker Arctic
Technology Inc., for operating in the most demanding icebreaking

An ice channel could be widened by one icebreaker or a double convoy.
The double convoy means that two icebreakers open or widen a channelside by side or one after the other. Such operation may require relatively

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