3.3. Finnish–Swedish winter navigation system (FSWNS)
The FSWNS governs the navigational operations performed each year at the Baltic Sea (Riska et al., 1997). It aims to ensure and increase the safety level of winter ice navigation in the area (Critch et al., 2013 and FTA, 2014b). For this purpose, the system limits and specifies on a yearly basis the merchant vessels which are entitled to assistance in the Baltic during the sea ice season and the eligible vessels for icebreaker assistance (FTSA, 2010). The FSWNS consists of five main components:
Ice class regulations: these specify technical requirements for ice-going vessels, i.e., the required engine output, hull strength and design, propeller shafts and gears, rudder and steering, and other technical requirements for the vessels belonging to specific ice classes.
Additional requirements: demands that complement the ice class regulations for navigating under ice conditions, including vessel loading and goods transport methods, correct positioning of the vessel propeller, the demanded engine power consumption by ice class, and functioning of cooling water systems.
Ice services: these provide the information needed to activate the traffic restrictions of the system and encompass monitoring of ice conditions and ice developments on a daily basis. The produced information is released as ice charts, satellite images, ice and weather reports and forecasts for the different areas within the Baltic Sea.
Traffic restrictions: these aim at ensuring vessel safety and the natural environment. The restrictions support a smooth ship traffic flow and reduce the time vessels have to wait for icebreaker assistance, by specifying e.g., tonnage restrictions for ships travelling to a certain port.
Icebreaker assistance: it begins with the provision of information, guidance and routing advice for vessels navigating independently in sea ice conditions. Conditional to the prevailing ice conditions, icebreakers may also provide on-site operational assistance, e.g., to free a ship which has become beset in ice, or to lead a convoy through challenging ice fields.