The possibility of monitoring traffic has improved considerably since the introduction of AIS. A much better view of what is going on at sea offers new possibilities to enhance shipping safety. The risk of each ship delivers the basis for taking measures according to UNCLOS and the precautionary principle, to ships that have a far more than average risk. Application of this principle requires a scientific approach for the determination of the risk. This paper describes how the risk index or alert value is calculated dynamically, de-pending on the geographical position, the ship characteristics, the environmental conditions, other ships, shal-lows and other obstacles as offshore platforms and wind farms.