A flag convention useful in port became unreliable at sea. Ships might be a mile or more apart, while funnels and superstructure could hide whether a signal flew to port or starboard. Line-abreast formations made the distinction still harder, so important orders needed a central, highly visible hoist rather than an assumed viewing angle. Fisher favoured one workable method that reduced complexity. Flags were a primary communication system in this period, while modern fleets more often use them as a redundant channel.
Notable Point · 8:19-13:03
Why flag-signalling rules for port failed at sea
Halyard position could convey meaning in a close anchorage, but distance, funnels, and changing formation made that convention unreliable at sea.