Analysis of information sources in references of the Wikipedia article "Blue sign" in English language version.
Blue Flagging. Especially on rivers, look out for ships or barges with a blue flag or board display on the starboard side of the wheelhouse.
… meetings are conducted what is colloquially known as 'blue boarding'
Lots of blue flagging, as upbound vessels try to stay in the shadow of the current, and call for starboard-to-starboard passing.
we had already rigged an arrangement for blue flagging—a flag of Oxbridge blue run up on the starboard side being an indication that a vessel proceeding downstream on the Rhine, Meuse, Main, Neckar, Lahn, Ems, Weser, Elbe or Seine wishes to meet an approaching ship starboard to starboard instead of port to port. Or, more simply, that the skipper is keeping to the left instead of the right because he wants the current, or can't steer properly
1.3.2. Navigation, short-term ahead … Navigation a short-term ahead is the decision phase in the navigation process. … — intention (blue sign),
Article 6.04 – Meeting: Normal rules … 4. Vessels proceeding upstream which leave the course of those proceeding downstream on their starboard side shall in good time and to starboard: … Display a light blue board in conjunction with a bright scintillating white light.
Article 3.03 – Boards, flags and pennants … rectangular. … (a) … neither the length nor the width is less than 1 m or, in the case of small craft, less than 0.60 m;
Lots of blue flagging, as upbound vessels try to stay in the shadow of the current, and call for starboard-to-starboard passing.
