The Evolution of Chartplotters & GPS - Fish Finders: Lead Line

Posted by Sharon Kemlage on

GPS Fish finders are neat pieces of equipment with complex modern features such as software algorithms. Some of them come with hundreds of functionalities, and learning how to use them is painstakingly complex. Before the emergence of this technology, its roots were humble. For depth measurement past fishers relied on the lead line for depth sounding (measuring of depth).

 The Lead Line (Sound Line)

 A lead line is a rope with a plummet, made of lead, attached at one end. It is one of the oldest navigation tools, with its first use, traced back to ancient civilizations; among them the Greeks and Romans. However, this was not the first device for measuring depth. Surprisingly, the stick was the first device used, with Egyptians using it on the river Nile. We can count ourselves lucky; we have GPS-fish finders with sonar technology.

 A leadsman would swing the device into the sea, either standing on the shrouds or the chains. To determine the depth the length of the line submerged in the water was measured. You could take the lead line and stretch it between your arms. The length of a full stretch was about six meters; referred to as the fathom. Instead of extending the cord every time, it became essential to mark it off using calico, leather, wool, and other materials. By 1600, English sailors were marking it in the order, 2, 3, 5, 7, 10, 17, 20, and 25. The standard line was 20 fathoms (120ft).

 The leadsman had to call out the depth with a loud voice as he retrieved the line. If the level fell precisely on the marked line, he would say, "By the mark" followed by the fathom. If he estimated the depth to fall between two lengths, he would say "by the deep" followed by the fathom. For a fraction, he would say "A quarter less seven," if the preceding number was seven. 

 Functions of the Lead Line

 Current chartplotters and lead lines shared same similar functions. At the bottom of the lead’s plummet, a hole was hollowed out to insert a wad of tallow or animal fat. Once deployed, it would bring up part of the ocean surface.

 Just as the land varies, sand, pebbles, and clays shells collected would allow the ship's crew to determine their location in the featureless sea. For instance, if the plumber came up clean, it meant that the bottom was composed of rocks. The device further guided the ship during anchoring and was useful for safety.

 Evolution of Modern Equipment

 Improvements to the lead line had to wait till the 19th Century. Edward Massey, a clockmaker from England, developed the first mechanized device for determining depth in 1802. The device called the sounding machine had a dial that would turn as it sank.

 Sailors continued to use the lead line technology, until the invention of echo sounding, in 1928, by Herbert Grove Dorsey. Like the modern chartplotters, it utilized sound waves in determining the depth. For modern navigation equipment visit our store for great recommendations

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