I was skipper of a yacht sailing downwind at about 5 knots on passage along the south coast of England. We became aware of a small open boat ahead of us. We watched it carefully for signs of movement; was he drifting or anchored? There were no obvious signals and we saw no fishing rods over the sides. We assumed that they had lines over the stern or were hauling pots.
I took a course to avoid a collision but not deviate too far off course. As we got near there was some frantic waving from the moored boat, so we deviated a little more but not too far as I thought that they may have been requiring assistance. As we passed, the shouting became abusive and they pointed to their code flag A. I tried to call them on the radio to point out that, according to ColRegs, they should have been displaying a solid shape capable of being seen from all directions. Their flag was streamed out downwind and not visible to us.
This emphasises the need for care when making assumptions both about your own actions being obvious to others and what you assume that others are doing. In retrospect, we realised that I should have given them more sea room although as a yacht at 5 knots we were making little wash. I should have given more thought to what they might have been doing rather than what I assumed they were doing. On the other hand, they should have given some thought to what we as a vessel approaching from upwind could see of their signal.
Although many diving boats indicate that they have divers down by flying flag “A”, this may not be obvious to other vessels approaching from upwind or downwind. Rule 27 provides for a rigid replica of Code flag A and that measures shall be taken to ensure all-round visibility. The signal should only be shown when the vessel is engaged in diving operations. Exhibiting it when the vessel is not so engaged may lead to disrespect for the signal.