Otso is a Finnish state-owned icebreaker. Built by Wärtsilä Helsinki shipyard in 1986 to replace the aging Karhu-class icebreakers, she was the first Finnish post-war icebreaker to be built without bow propellers. Otso has an identical sister ship, Kontio, which was delivered in 1987.
Development and construction
In the early 1980s, the Finnish National Board of Navigation began looking for a replacement for the aging Karhu-class icebreakers Karhu, Murtaja and Sampo which had been built in the late 1950s and were no longer wide enough to escort modern merchant ships. Furthermore, the old icebreakers were expensive to operate and, despite their small size, required a relatively large crew of 53. The development of the new class of icebreakers, dubbed Karhu II in the preliminary papers, intensified when Wärtsilä opened a new ice model test facility in 1983. The tenth post-war icebreaker of Finland was ordered from Wärtsilä Helsinki shipyard on 19 March 1984 with a price of FIM 235 million. The ship was launched on 12 July 1985 and delivered to the owners on 30 January 1986. Her name, Otso, is one of the many terms for bear in the Finnish language. In January 1987, Otso was followed by a similarly-named sister ship, Kontio, after which the three Karhu-class icebreakers were decommissioned and sold.
During extensive ice trials in the Bothnian Bay in March 1986, Otso was put through a series of test to determine her icebreaking capability. In a race against the 1975-built Urho in level ice, Otso beat the older but more powerful four-propelled icebreaker by more than a ship's length, showing that in terms of ice resistance the new icebreaker was superior to her predecessor. In ice, she could easily maintain a speed of and small ice ridges along the way appeared to be of no consequence to the vessel. However, the strength of the new icebreaker was put to the ultimate test when she encountered a large pressure ridge reaching all the way to the seafloor some below the surface. After preparations, Otso was accelerated to a speed of and rammed into the ridge at full power. Since the new icebreaker had a smooth inclined stem and lacked the bow propellers of her predecessors, she rode up the ridge and began listing to the port side as the hull rose from the water. After coming to a stop, Otso slid back by herself without utilizing the engines, and the ridge was penetrated on the second charge. The robustness of the ship and its propulsion system were further proven when the icebreaker was backed into a ridge at "to prove to the customer it doesn't break".
Considered to be a successful design that incorporated the latest Finnish icebreaker technology, Otso was later used as a design basis for the United States Coast Guard icebreaker Healy.{
Technical details
General characteristics
Although the Otso is slightly shorter than her predecessors Urho and Sisu, she is slightly wider and was, at the time of her delivery, the widest subarctic icebreaker in the world with a beam of . However, with a maximum draft of and a minimum operating draft of only , Otso is able to escort ships to shallower ports than her predecessors. The displacement of the icebreaker is 9,222 tonnes.
In many ways, Otso was a significant departure from the traditional Finnish icebreaker design. The extended bridge wings on top of the stylish superstructure feature full-depth all-round windows that provide almost 360 degree visibility from the main steering position, which has been moved to the starboard bridge wing from the centerline. Furthermore, the traditional colours dating back to the Imperial Russian era, yellow and black, were replaced with the colors of the flag of Finland, blue and white. Due to the extensive use of advanced automation, which allowed everything ranging from starting and stopping the main engines to raising and lowering the flag to be done remotely from the bridge, Otso had the smallest crew among Finnish state-owned icebreakers when she entered service in 1986. Later her crew has been further reduced to 20. Otso was also the first icebreaker in which the lifeboats, unusable in ice-covered waters, were replaced with inflatable life rafts that could be lowered on the ice.
While Otso holds the highest Finnish-Swedish ice class, 1A Super, it has hardly any meaning for icebreakers which are of considerably stronger build than merchant ships operating in their care. Coated with low-friction Inerta160 epoxy paint, the hull plating has thickness of over in the bow and the waterline is protected by an explosion welded stainless steel compound plating that further reduces ice friction and resists abrasion. Galvanic corrosion is prevented by active cathodic protection.