This icebreaker in the Urho class is identical to her sister ship, with the exception that the accommodation on Urho was reserved for PR purposes, whereas on Sisu they were fitted for classroom use from the beginning, to be used by maritime students.
By combining the vessel's cafeteria with the adjoining auditorium, a room accommodating 40 people can be created. The vessel was designed to incorporate quarters for 54 crewmembers, each with a single cabin. The cabins for the officers also include a private WC/shower. The ship also has a library, a gym, two saunas and a swimming pool.
Today, when the vessel is engaged in ice-breaking operations, the number of crew onboard is 21. Through automation and by the introduction of effective work practices, less than half of the original crew is required to operate the ship! When Sisu is deployed on ice-breaking assignments, the vessel's crew works on a schedule of six hours of work, followed by six hours of rest. This cycle is repeated for 20 days, after which the crew have 10 days' leave.
The main engines of the ship comprise five Pielstick 12 PC 2-5V V diesel engines, manufactured under license at the Wärtsilä shipyard in Turku. Each cylinder has a bore of 400 mm, with a stroke of 460 mm. Each engine powers an AC generator, which, in turn, power the four engines driving the propellers.
At full power, the two rear propellers receive 60% of the power, which leaves 40% for the two fore propellers. The fore propellers rotate inwards, thrusting water under the hull when the vessel is travelling forward.
Water flowing along the vessel's sides helps to reduce friction between the ship's hull and ice. The rear propellers rotate outwards, causing the crushed ice to be thrust under the unbroken ice sheet, allowing the broken channel to remain open.
The main generators, the engines driving the propellers, the auxiliary generators and the control equipment for the machinery were manufactured by Strömberg. The ship's engine room is unmanned; only the control room is manned.
The bridge offers 360-degree visibility, making it easier to maintain visual contact with a ship on tow. In addition, the vessel is equipped with a heeling mechanism for improved ice-breaking capability in severe ice conditions. Three pumps transfer water onboard the vessel, allowing it to heel thirteen degrees in just 50 seconds.
In 1982, Sisu underwent modification at the Wärtsilä shipyard in Turku to burn heavy fuel oil. The cost of the modification was 3.8 million Finnish markka; however, it was calculated that reduced operational costs would make up for the modification costs during a single ice-breaking season.
Another modification, the alteration of Sisu's bridge, was completed in December 1988, at the Kotka repair yard of Wärtsilä Meriteollisuus.