NavList:

Throwing a floating object overboard and timing its passage down the ship's side between two points a known distance apart is known as a "Dutchman's Log".

Many years ago, when I was piloting a large Japanese tanker into a conventional sea berth, the Master had one of the crew, 700 feet away on the focsle head, throwing small pieces of wood overboard. As the chunk of wood passed directly beneath the bridge wing, the Mate on watch consulted his stopwatch and tables of speeds against time and distance, reporting the result to me in knots and tenths.
All this well before doppler logs and differential GPS, of course.

This routine probably had something to do with a certain lack of confidence in my approach speed, due to the fact that I was at least 30 years younger than most Japanese Pilots - who were then recruited from the ranks of retired shipmasters.
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