Overview

The assistance icebreakers operating in the Baltic Sea can be divided into large icebreakers (A-class) that can perform in all ice conditions, including the harshest conditions encountered in the northernmost Bay of Bothnia during severe winters, and smaller (B-class) icebreakers that are mainly used in the Gulf of Finland and Sea of Bothnia. The main difference in assistance capability between A-class and B-class icebreakers is mainly the width of the channel that the icebreaker breaks. This is an important difference since merchant vessels have varying beams. The wider the channel, the easier it is for the merchant vessel to follow.

Currently, the project partners’ icebreaker fleet consists of only three B-class icebreakers, two of which are reaching the end of their operational life. As these icebreakers are smaller in size, and especially beam and engine power, they are more cost-effective to operate than the large icebreakers. Also, due to the more frequently occurring mild winters in the Baltic, there is a need for a more versatile icebreaker fleet that can be operated in a flexible way without compromising neither the safety nor the fluency of the winter navigation system.

Therefore, the objective of work package 3 is to investigate and address the need for smaller, more environmentally friendly B-class icebreakers in Estonia, Finland, and Sweden. This will be done by conducting studies that accommodate new demands and requirements.

Task 3.1 – Concept design study of smaller icebreaker (B-class)

The aim of this task is to conduct a study on different design concepts for a smaller icebreaker. The study will serve as decision-making tool on replacing the current B-class icebreaker(s) in the Baltic fleet: Voima (in Finland) and Tarmo (in Estonia).

Based on an already conducted pre-study, listing, and comparing the benefits and disadvantages of different design concepts for a cost-efficient B-class icebreaker, a more in-depth concept study will be performed to get a better understanding of the cost and performance of these concepts.

The study will focus on three different concepts that will be developed further to a concept design stage i.e., preliminary design with rough estimates of capacities and ensured icebreaking and assistance capability. The study will compare, rank, and evaluate the performance and capabilities of the selected concepts, particularly those related to assistance icebreaker capability, including at least manoeuvrability (turning capability in ice), towing capability, and capability to create a wider channel (channel width) than the icebreaker’s hull for assisting larger vessels.

The concepts that will be studied, are all classified as B-class icebreakers, but requirements are somewhat higher, introducing the B+ concept, which is an improvement to the B-class icebreaker in assistance performance and environmental impact, yet still accomplishing low-cost levels. This enables the icebreaker to operate also in the northernmost Bay of Bothnia in early winter ice conditions and move southwards to easier conditions as the winter progresses, providing the winter navigation system with fluency and safety.

For dimensioning the icebreaker properties and setting a basis for the study, the Gulf of Finland will be used as an operational area starting point. The study will also make cost estimates of the selected concepts as well as rough concept drawings and technical specifications. In addition, alternative fuels to be used for the icebreaker will be studied as part of the concept study, considering fuel availability in the Baltic, their feasibility for icebreaker purpose and technical readiness of the available and suitable machinery equipment.

Task 3.2 – Ice model trails

The aim of this task is to verify performance predictions of selected design concepts in the concept study above, by testing them in ice in a model basin, as it is expected that the concepts ranked as best in the study, might be quite similar in their predicted assistance icebreaker capabilities, but might also contain new and not tested features.

Therefore, one to three of the selected concepts will be tested with the ice model trials. This approach ensures that possible innovative solutions can be implemented into future icebreaker design without the fear of reducing the actual icebreaker performance.

Based on the results of the trials, the concept(s) will be altered, if need be, to better fulfil the requirements of a B-class icebreaker. This verification process gives credibility to the procurement of building a B-class icebreaker (outside the project’s scope).

Task 3.3 – Study on adjustable towing notch

There are several factors that influence the design of the towing notches of the icebreakers. The changes in the merchant fleet (all cargo and passenger vessels transporting goods at sea) have been guided by the environmental legislation already for a longer period, and these rarely coincide with the requirements and needs of the merchant vessels from the winter navigation system’s perspective.

There is a growing ice classed merchant fleet with open water optimized bow forms sailing the Baltic waters, which means that the vessels will at some point be assisted and possibly also towed. The open water bow shape can be considerably different from older bow shapes, for which the icebreakers’ towing notches have been designed for and raises a need to study the adjustability in the icebreaker fleet’s towing notches.

Another factor setting requirement on an icebreaker’s towing notch is the varying size of the merchant fleet vessels. The icebreakers can be trimmed to a better position for fitting the towed vessel bow in the icebreaker towing notch, but this can weaken the icebreaker’s performance and even stability. In addition, it can also increase fuel consumption thus leading to higher emissions.
Therefore, the aim of this task is to conduct a feasibility study to explore if an adjustable towing notch is a possible solution to address the above-mentioned factors. The study will examine the feasibility and the cost of implementing adjustable towing notch to existing and newbuild icebreakers, to be able to better assist and tow merchant vessels. It will explore how the icebreaker performance can be maintained at optimal level while being able to adjust towing notch height without having to trim the icebreaker aft up or down.

The feasibility study will also set ground for gaining a better understanding of the costs, benefits, structures, and especially required procedures and modifications on existing icebreakers to equip them with an adjustable towing notch. Based on the results of the feasibility study, including cost and suitability of the icebreaker towing notch, a pilot project could be initiated during the building phase of the new B-class icebreaker (not in scope of the project) to verify the solution. If the solution turns out to be beneficial, it can be later adapted to other icebreakers.