How applicable is POLARIS to the ice-covered Northern Baltic Sea?

The Polar Operational Limit Assessment Risk Indexing System (POLARIS) provides a structured and widely recognized framework for evaluating navigational safety in ice-covered waters. Its integration into the IMO Polar Code reflects its importance in supporting voyage planning and risk mitigation in Arctic and Antarctic contexts. However, the applicability of POLARIS to sub-Arctic seas with distinct operational characteristics, such as the Northern Baltic Sea, remains largely unexplored. This study provides a systematic investigation of POLARIS in this region utilizing a combination of high-resolution ice data, detailed historical hull damage records, and operational icebreaker assistance logs, offering both quantitative validation and practical insight into POLARIS performance. The dual comparison with real-world damage incidents and captain-driven icebreaker requests enables a uniquely holistic evaluation of how well POLARIS-derived Risk Index Outcomes (RIOs) reflect actual navigational risk. The analysis reveals that POLARIS generally underestimates operational risks in this region, especially for ships with higher ice classes (IAS, IA, and IB), which are assumed to tolerate harsher conditions but in reality still encounter significant limitations. This discrepancy aligns with prior findings that have pointed to the system's “flexibility” in Arctic applications, and it further underscores the need for region-specific calibration. In light of these results, a downward adjustment of the Risk Index Values (RIVs) is recommended for use in the Northern Baltic context to improve alignment between calculated and perceived risk levels.