A blue sign or blue board is used by inland waterways vessels within the

Trans-European Inland Waterway network The Trans-European Inland Waterway network is one of a number of the Trans-European Transport Networks (TEN-T) of the European Union. According to Article 11 of the Decision No 1692/96/EC of the European Parliament and of the Council of 23 July 1 ...

when performing a special manoeuvre or passing on the starboard side. On navigable waterways vessels normally pass each other on the

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Ham ...

-side, so the display of the blue sign and flashing white light signal intention to pass each other on the

starboard Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front). Vessels with bilateral symmetry have left and right halves which are ...

-side. This process is known as blue boarding or historically blue flagging. The ' (CEVNI) regulations require upstream vessels operating on the opposite side to display a light-blue sign and scintillating (flashing) white light. Article 3.03 states that the board must be rectangular and 1-metre × 1-metre for large vessels, or 0.6-metres × 0.6-metres for small vessels. The presence and status of the blue sign is transmitted by the ship's Inland- Automatic Identification System (Inland-AIS) transponder to other vessels. The status of the sign is transmitted using two bits of the "regional application flags"/"special manoeuvre field" in the AIS position reports. This must be transmitted every ten seconds.

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Water transport in Europe Nautical terminology Maritime education {{europe-transport-stub