AIS (Automatic Identification System) data includes, among other things, the location, speed, course and heading of the reporting ship. A steaming ship transmits AIS messages every few seconds. In the Baltic most messages are received and stored by terrestial stations. This data includes tens of thousands ice transits to ports each year. When combined with ice cover information the data opens almost limitless possibilities to study performance of individual ships, navigational situations, and the whole winter navigation system. As the amount of data is very large, it is possible to impose very strict conditions on the identifiability of navigational situations and still have a dataset large enough for reliable analysis. Results based on all ice navigation during season 2010-2011, as identified from Finnish terrestrial AIS data, are presented. The ice data consists of daily ice charts gridded to 1 NM resolution. Each AIS message is linked with the ice chart variables in the nearest grid node. The particulars of the ships are obtained from a database. As an example the subset of cases of unassisted navigation is studied and the performance of different ice classes are compared. For 1A super vessels relationships between ice conditions and ship speed reduction, or ice resistance, can be extracted. For ships in lower ice classes the results are less straightforward as the ships typically must increase their power setting to maintain certain minimum speed in increasingly difficult conditions. That the power data is not included is the main shortcoming when AIS data is used to estimate ice resistance. Possible methods to get around this shortcoming are exemplified.
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