The harbor master notes wind route by using flying flags, jotting angles as masts clink and buoys bob on tender swells.

https://mylessjwo723.zenbloomer.com/posts/from-revolution-to-today-how-and-why-the-american-flag-has-transformed-2

The harbor master notes wind direction by way of flying flags, jotting angles as masts clink and buoys bob on delicate swells.