In the years of sailing ships, the Dutchman's log was an
early method of calculating ship speed. An object that
would float was thrown into the water near the forward
part of a ship. In the after, or rear, section, a sailor
with a sandglass noted the time taken for the ship to
pass the object floating in the water. From the time and
the known distance between the two points on the ship, a
rough calculation was made of the ship's speed.
