# Simulation Tool for Winter Navigation Decision Support in the Baltic Sea
## 3 Scope of the Model  
As mentioned earlier, the tool aims to help answer some of the questions regarding icebreaker operations for potential future scenarios. An important question for the stakeholders would be the determination of the number of icebreakers required with expected climatic and environmental changes. Along with the changes in ice conditions and therefore the operating speeds of vessels, the climate threat has also resulted in policy changes, which will affect the ice-going capacities of vessels. This simulation model would provide a critical bird's-eye view of the winter navigation system.  
To effectively capture the challenges of navigation, it is important to model ice conditions appropriately. There are multiple aspects of ice information, such as thickness, concentration, and topography. The information is available through ice charts published by the Finnish Meteorological Institute (FMI). However, the data are from multiple sources, such that different file formats need to be processed together to obtain a complete picture of ice conditions. The ice data are also highly dynamic and new ice information is available for each hour of each day, for every square mile of geographical area. For use in this model, this information is suitably aggregated, to ensure an acceptable compromise between the level of detail and model computational time. The vessels modeled in the simulation need to be sensitive to these ice changes and adapt their speeds (or stop) in response to the conditions. This requires a mechanism for the vessels to monitor ice parameters and evaluate their response several times during a single trip. For this, hv curves and equivalent ice thickness concepts are used. Equivalent ice thickness uses a mathematical formula that gives a single value of ice thickness based on ice concentration, thickness, and topography. The model uses the formula given by [PERSON] et al. [14] for calculating the equivalent ice thickness. An hv curve is a polynomial regression that describes the variation in speed of a vessel as a function of ice thickness. Each vessel has an hv curve profile, based on its dimensions. The hv curves are modeled as entity attributes, and they evaluate changing speeds based on equivalent ice thickness values. Examples of hv curves are shown in Section 4, Figure 2.  
The framework being developed is applicable to the entire Baltic Sea Region. However, to demonstrate a proof of concept and to validate the functionalities, a smaller region of high ice variation and traffic flow is selected and presented in this paper. The area of interest for this model is the Bay of Bothnia, with the Finnish and Swedish borders on either side. The traffic in this region is cooperatively managed by both Finland and Sweden. All vessel journeys calling on Finnish ports have been included. Some of these journeys originate or terminate outside the operating zone under consideration. The data have been processed to prune the vessel journeys outside the Bay of Bothnia. Following the approach of Bergstrom and Kujala [15], the southern point of Kvarken was selected as an entry and exit point to and from the operational area. The case study discussed in this article focuses on operations at Finnish ports. Hence, only trips to and from Finnish ports are considered.  
More details about the input data are presented in the next section.  
Figure 2: Plots of HV curves. (**A**) Vessel assisted at a distance. (**B**) Vessel in level ice.