20 " 2 knots.
25 " 1 knot.
30 " 3 knots.
35 " 1 knot.
40 " 4 knots.
9 " are called mark.
11 " are called deeps.
The leadsman stands on his little grating and swings the lead so it just clears the water. When it is swinging well he lets it fly in the direction in which the ship is moving and then notes the depth by the strips of leather or rags. The result is shouted out so the steersman can hear and keep the vessel in the channel.