Navigation and Seamanship

3.1.1. Introduction

Depth measurement could be done by two ways one is mechanical another one is electronic. In the ancient days mechanical device- lead line was used to measure the depth. The lead-line is the oldest navigational instrument and was used by the ancient Egyptians. Lead lines are used in shallow waters even today by traditional fishermen in different parts of the world.

The common electronic instrument used for measuring the depth is echo sounder; of course this was introduced only after the Second World War. The lead line is also called as hand lead line, is the oldest and most reliable depth-finding device for shallow waters. Lead line is for taking soundings (which means measuring the depth of water) up to 20 fathoms ( 120 feet) . But the deep sea lead line is used to measure depth up to 100 fathoms or more. The principle of lead line is very simple. A weight (generally lead) is lowered to the sea bed by a graduated line. The length of rope immersed gives the depth measurement of water.