Sounding line
Encyclopedia
A sounding line or lead line is a length of thin rope
with a plummet
, generally of lead
, at its end. Regardless of the actual composition of the plummet, it is still called a "lead."
Sounding lines were widely used in navigation
until the development of echo sounding
. Ultrasonic depth sounders provide an accurate graphical profile of the depth of the seabed.
The word derives from the Old English sund, meaning swimming, water, sea; it not related to the word sound
in the sense of noise or tones.
s by repeatedly stretching the rope between the two outstretched arms. Water depths have traditionally been measured this way using a weighted sounding line. The word fathom can be used as a verb to describe this process.
At sea, in order to avoid repeatedly hauling in and measuring the wet line by stretching it out with one's arms, it became traditional to tie marks at intervals along the line. These marks were made of leather
, calico
, serge
and other materials, and so shaped and attached that it was possible to "read" them on sight by day or at night by the feel of each one. The marks were at every second or third fathom, in a traditional order: at 2, 3, 5, 7, 10, 13, 15, 17, and 20 fathoms. The "leadsman" called out the depth as he read it off the line. If the depth was at a mark he would call "by the mark" followed by the number, if the depth was between two marks, he would call "by the deep" followed by the estimated number.
On the Mississippi River
in the 1850s, the leadsmen also used old-fashioned words for some of the numbers; for example instead of "two" they would say "twain". Thus when there were only two fathoms left under the boat they would call "by the mark twain!". The American writer Mark Twain
, a former river pilot, likely took his pen name
from this cry.
Sometimes tallow
was placed at the recess in the bottom of the plummet to pick up traces of any loose material (such as mud
, sand
, or shingle
) from the seabed
, providing information useful for pilotage
and anchoring
. If the plummet came up clean, it meant the bottom was rock
. Nautical chart
s now provide information of the seabed materials at particular locations.
Rope
A rope is a length of fibres, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength...
with a plummet
Plumb-bob
A plumb-bob or a plummet is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb-line....
, generally of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, at its end. Regardless of the actual composition of the plummet, it is still called a "lead."
Sounding lines were widely used in navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
until the development of echo sounding
Echo sounding
Echo sounding is the technique of using sound pulses directed from the surface or from a submarine vertically down to measure the distance to the bottom by means of sound waves. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes...
. Ultrasonic depth sounders provide an accurate graphical profile of the depth of the seabed.
The word derives from the Old English sund, meaning swimming, water, sea; it not related to the word sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
in the sense of noise or tones.
Sounding technique
It is easy to measure a length of line or rope as a rough number of fathomFathom
A fathom is a unit of length in the imperial and the U.S. customary systems, used especially for measuring the depth of water.There are 2 yards in an imperial or U.S. fathom...
s by repeatedly stretching the rope between the two outstretched arms. Water depths have traditionally been measured this way using a weighted sounding line. The word fathom can be used as a verb to describe this process.
At sea, in order to avoid repeatedly hauling in and measuring the wet line by stretching it out with one's arms, it became traditional to tie marks at intervals along the line. These marks were made of leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, calico
Calico (fabric)
Calico is a plain-woven textile made from unbleached, and often not fully processed, cotton. It may contain unseparated husk parts, for example. The fabric is less coarse and thick than canvas or denim, but owing to its unfinished and undyed appearance, it is still very cheap. Originally from the...
, serge
Serge
Serge is a type of twill fabric that has diagonal lines or ridges on both sides, made with a two-up, two-down weave. The worsted variety is used in making military uniforms, suits, great coats and trench coats. Its counterpart, silk serge, is used for linings. French serge is a softer, finer variety...
and other materials, and so shaped and attached that it was possible to "read" them on sight by day or at night by the feel of each one. The marks were at every second or third fathom, in a traditional order: at 2, 3, 5, 7, 10, 13, 15, 17, and 20 fathoms. The "leadsman" called out the depth as he read it off the line. If the depth was at a mark he would call "by the mark" followed by the number, if the depth was between two marks, he would call "by the deep" followed by the estimated number.
On the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
in the 1850s, the leadsmen also used old-fashioned words for some of the numbers; for example instead of "two" they would say "twain". Thus when there were only two fathoms left under the boat they would call "by the mark twain!". The American writer Mark Twain
Mark Twain
Samuel Langhorne Clemens , better known by his pen name Mark Twain, was an American author and humorist...
, a former river pilot, likely took his pen name
Pen name
A pen name, nom de plume, or literary double, is a pseudonym adopted by an author. A pen name may be used to make the author's name more distinctive, to disguise his or her gender, to distance an author from some or all of his or her works, to protect the author from retribution for his or her...
from this cry.
Sometimes tallow
Tallow
Tallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.In industry,...
was placed at the recess in the bottom of the plummet to pick up traces of any loose material (such as mud
Mud
Mud is a mixture of water and some combination of soil, silt, and clay. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone . When geological deposits of mud are formed in estuaries the resultant layers are termed bay muds...
, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, or shingle
Shingle beach
A shingle beach is a beach which is armoured with pebbles or small- to medium-sized cobbles. Typically, the stone composition may grade from characteristic sizes ranging from two to 200 mm diameter....
) from the seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...
, providing information useful for pilotage
Pilotage
Pilotage is the use of fixed visual references on the ground or sea by means of sight or radar to guide oneself to a destination, sometimes with the help of a map or nautical chart. People use pilotage for activities such as guiding vessels and aircraft, hiking and Scuba diving...
and anchoring
Anchor
An anchor is a device, normally made of metal, that is used to connect a vessel to the bed of a body of water to prevent the vessel from drifting due to wind or current. The word derives from Latin ancora, which itself comes from the Greek ἄγκυρα .Anchors can either be temporary or permanent...
. If the plummet came up clean, it meant the bottom was rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
. Nautical chart
Nautical chart
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land , natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids...
s now provide information of the seabed materials at particular locations.
External links
- An explanation of the fathom marks used at sea (retrieved Sept 2006).