Multipurpose icebreakers Fennica & Nordica

Design of the multipurpose icebreakers

In 1989, the Finnish Maritime Administration chose our company, whose official name at the time was engineering firm Lehtonen & Siirilä Oy, as the designer of the budgeted new icebreakers. We had solid experience in designing and also building Arctic service and research vessels: we all came from the shipyard called Oy Laivateollisuus Ab in Turku, which was closed the previous year. The design contract was concluded on 13 March 1990. The goal was to design an icebreaker that meets as well as possible the requirements set by the customer’s experts for the new icebreaker.

We started the design work under the working name Tarmo 2. The main requirements for the ship were determined by the Finnish Maritime Administration’s working group, within whose scope Mr. Arjo Harjula, chief engineer of the Finnish Maritime Administration, was assigned to supervise the design work. The work was very confidential, because in addition to the Helsinki shipyard, both Rauma shipyards had also signed up as willing construction yards in Finland. Everyone had to be given the basis for making offers equally and at the same time, so that no one would have an advantage in the bidding process. Our work went quickly under Mr. Harjula’s supervision. Planning entities and different options were weighed in several meetings. The concept plan with specifications and drawings was ready for the final approval of the working group at the end of June 1990.

The document handover ceremony was arranged to take place at Finnish Maritime Administration’s facilities in Helsinki on June 18, 1990 at 1:00 p.m., according to the schedule of maritime advisor, Mr. Lennart Hagelstam. To our great horror and surprise, he started the meeting by telling us that according to the decision of the working group, the project Tarmo 2 has been abandoned and the material made for it will go to the trash can! After a long silence, he continued: “Now let’s start the work again. Let’s make a plan for an icebreaker that can operate on the open sea in a storm and that can do all kinds of work and make money in the open water season”.

Although further work was of course welcome for us, we did have to state at the meeting that the proposal is good, but its implementation is impossible. Mr. Hagelstam emphasized that the customer defines the requirements and the designer’s task is to implement them. We promised to do our best, and so it was agreed to restart the design work of the “multipurpose icebreaker” under the same conditions as the Tarmo 2 design had been implemented.

The summer period operational profile of the vessel was defined by the offshore markets’ needs. Most of all, there was a demand for vessels that could conduct flexible pipe and cable laying and trenching and ploughing of cables and pipelines. Other defined tasks were e.g. cable repair work, anchor handling and the moving of offshore oil drilling platforms, semi-submersible units, and other offshore units, and transportation of deck cargo.

It was clear from the beginning that the hull form of the icebreakers of that time was not suitable for an open water vessel. The biggest problem was the large width required. The ship had to break a channel as wide as the aided merchant ships of the time needed – at least about 24 meters. A vessel making such a wide channel had to be at least as effective an icebreaker as the previous Urho and Otso class icebreakers, and on the other hand, open water characteristics at least as good as the best and biggest offshore maintenance vessels working in the North Sea. Mr. Hagelstam and Mr. Harjula did not give up on this requirement – it became the main principle of the entire design work. Experts from the Maritime Administration took an active part in planning – not only in supervision, but also in finding solutions.

We designed and made calculations for several options, whose properties we evaluated together. The rolling of an icebreaker in the open sea was a difficult question, for which it was not possible to come up with an acceptable and surely working solution. We concluded that the width of the icebreaker, the large weight of the hull and the location of the center of gravity at the bottom, the shape of the hull and the limited draft result in unbearable rolling acceleration in open water. What could be changed? The conclusion of the design team was that the idea of ​​raising the center of gravity of the ship by mounting the main engines as high as possible, as in the Otso class, was good, but not nearly enough. We stated that the width of the ship must be reduced.

The design team came up with the idea of ​​a ship whose width would be large as an icebreaker (24m) and significantly smaller by 3-4m in open water operations – the ship would have long removable tanks on both sides. This proposal seemed like a computationally and theoretically acceptable solution, and we decided to conduct preliminary model tests to verify both the open water and icebreaking properties. The results were promising, but concretely, such a structure would be really difficult and unfeasible.

The design team came up with the idea of ​​a ship where only the bow is wide and the midship and stern are narrower: “In order to reduce the height of the metacentric height, the whole ship does not have to be narrow!” The whole design team got excited about this and the solution was close to success. In the open water model tests, it became clear that rolling still needs to be reduced. It was decided to try a plan where large bilge steps would be built in the lower part of the narrower stern to dampen the rolling motion.

In the ice model tests, it was found that due to the narrow stern, the turning of the icebreaker and the agility of assistance operations were not as good as in the Otso class. The design team decided to try azimuthing thrusters for the developed two-width hull form. In this case, the entire thrust of the thrusters would be achieved in the side direction as well, in which case the turning force would be significantly greater than when using rudders. Azimuth propulsion had already been found to be a viable solution in smaller fairway maintenance vessels. However, the design team was troubled by the solution’s big departure from known icebreaker technology: A two-width icebreaker with two outboard engines!

Based on strict selection criteria, Ugland AS from Norway was chosen as the summertime charterer. We also received strict requirements from them and also advice on designing open water features. We loaned Ugland’s new hull model of a large North Sea supply vessel. This provided a benchmark for open water behavior.

A total of 150 model tests were conducted in the test pools of both the University of Technology and VTT.

The conceptual design had been extended so far that with calculations and model tests we could demonstrate that the client’s main criteria were fulfilled: The icebreaking capability of the ship was at least as good as that of the Urho- and Otso-class icebreakers, speed in 80 cm level ice 8 knots. Maneuverability with a completely new two-width hull shape and 360ᵒ rotating azimuth propulsion devices showed that the diameter of the ship’s turning circle at full speed in a field of 65cm level ice and 20cm snow is only about 150 m (1.3 x the ship’s length). Open water speed was proven to be at least 16 knots. The ship’s roll behavior in North Sea side wave conditions was even better than that of a new large OSV. The difference to the Urho and Otso class icebreakers in this respect was naturally dramatic.

After the solution had been tried in several model tests, it was finally approved for implementation. Criticism in the public was, as expected, harsh: “Outboard motor breaker”, “Moulinex” and “Vispilä” were the descriptions used even in the discourse of icebreaking sector professionals. However, the Finnish Maritime Administration set this bold concept plan as the basis of the requests for tenders sent to the shipyards in such a way that the shipyards were also given the opportunity to alternatively offer another similar concept if they so desired.

Three shipyards, two from Finland and one from Germany, participated in the tender for the construction of two sister ships. The Helsinki shipyard’s offer included both the shipyard’s own proposal and the ship’s construction offer according to the concept. At the end of a tight competition, the construction contract was awarded to Rauma’s Finnyards shipyard, whose offer was in line with the concept. It also met all the requirements and was also the cheapest of the offers given. The German Shipyard did not leave an offer at all.

We also participated as a consultant to the client in the construction and trials of the ships. The first ship, Fennica, was delivered from Finnyards Rauma Shipyard in March 1993, and the second, Nordica, in January 1994. The vessels were appreciated by their crews, and by the offshore clients. For example, in 1997, the First Officer of Nordica described the seakeeping characteristics like this: ”Our clients have complimented Nordica’s abilities as an offshore vessel, especially its good seakeeping abilities.” The Master of Nordica stated the same year that the ships function well in both in offshore work and icebreaking.

The design of the multipurpose icebreakers created a completely new way of thinking in the design of icebreakers. Today, almost all icebreakers being built have at least reasonably good open water characteristics, and almost all of them have azimuthing type propulsion.