Baltic Sea Ice Climate Workshop 2005 
68 
Winter Shipping 
Sea ice in the Baltic Sea is not just a natural or climatologically phenomenon. However, in an 
intra-continental environment, which is since many centuries a focus of human development 
and cultural interconnections resulting in ever increasing trade and traffic, the sea ice cover of 
the Baltic Sea was always a very important and restrictive parameter for the navigation. The 
main facts are summarized in Table 1. 
Table 1. Development of winter navigation in the Baltic Sea 
• At times of sailing vessels no ice navigation: the length of ice season was nearly 
equal to the period of closed navigation. 
• No essential changes in the early days of iron and steam vessels. 
• At the end of the 19 th century construction of first icebreakers. 
• In the beginning of 20 th century increasing navigation under light ice conditions, 
however, under more difficult conditions only ‘running fights’ to prevent ships to 
be beset and wintering in the ice area. 
• Between the World Wars I and II extending navigation periods in the southern 
areas including the Gulf of Finland up to permanent winter navigation - beside in 
the more severe winters. 
• Above was extended by increasing icebreaker fleets (due to economic 
pressure), improved vessels (ice strengthening), and adequate regulations for 
winter navigation 
in the fifties and sixties to the Sea of Bothnia, and 
in early the seventies to the northern Gulf of Bothnia. 
• Since more than 30 years (restricted) navigation during the whole ice season. 
• Today some ten thousand port calls per ice season. 
These events are partly documented in Figure 1, which shows the strength of the joint Finnish 
and Swedish State icebreaker fleet (total number and horse powers) as well as the five years 
running means for the closing days of the harbours Lulea and Oulu in the northern Bay of 
Bothnia and the maximum ice extent of the Baltic Sea for the period 1930 to 1977. From the 
beginning of the thirties to the beginning of the fifties the joint icebreaker fleet consists of 7 to 9 
icebreakers with up to 45,000 HP in total. The harbours Lulea and Oulu were closed between 
about 100 to 175 days depending on the severity of the ice winter with a slightly decreasing 
tendency. From the beginning of the fifties to the mid sixties the total number of the icebreakers 
were only increased by three up to 12, however, by replacing the older units by more powerful 
ones the total capacity was more than doubled to nearly 100,000 HP. By that the number of 
closing days for the mentioned harbours could be reduced to 80 to 110.