ot Honda Point Disaster

Sailing ships tossed a thing on a string (a "log") off the stern and literally counted knots with an hourglass for the timebase. That was used with compass headings for dead-reckoning navigation.

The book is worth reading. The fleet navigator was a prime fathead. When told about the RDF readings, he assumed they were reciprocal errors and turned east before the channel, onto the rocks.

There is a trick to combine e and h fields to eliminate the RDF reciprocal error, but he was still a fathead. RDF was the first way to navigate in fog, except for foghorns and soundings near shore.