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A fathom is a unit of length in the imperial and the U.S. customary systems equal to 6 feet (1.8288 m), used especially for measuring the depth of water. [1] The fathom is neither an international standard (SI) unit, nor an internationally accepted non-SI unit. Historically it was the maritime measure of depth in the English-speaking world but ...
The first practical fathometer (literally "fathom measurer"), which determined water depth by measuring the time required for an echo to return from a high-pitched sound sent through the water and reflected from the sea floor, was invented by Herbert Grove Dorsey and patented in 1928. [10]
≡ Time of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at 0 K [8] (but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of 299 792 458 metres. (SI base unit) shake: ≡ 10 −8 s = 10 ns ...
Depths which have been measured are indicated by the numbers shown on the chart. Depths on charts published in most parts of the world use metres. Older charts, as well as those published by the United States government, may use feet or fathoms. Depth contour lines show the shape of underwater relief. Coloured areas of the sea emphasise shallow ...
Many ships used knots spaced 8 fathoms (48 feet or 14.6 meters) apart, while other ships used the 7-fathom prescription. [8] The time interval needs to be adjusted according to the distance between knots. Substituting 6,000 feet for 1 mile, the above formula yields 28.8 seconds for a distance of 8 fathoms.
Time for another subfreezing day at the office, fishing 15 miles or so off the Massachusetts coast. ... Probably 60-40.” ... The giant nets are dropped 100 fathoms, or 600 feet, to the ocean ...
In general, a wide swath, which is depth dependent, allows a boat to map more seafloor in less time than a single-beam echosounder by making fewer passes. The beams update many times per second (typically 0.1–50 Hz depending on water depth), allowing faster boat speed while maintaining 100% coverage of the seafloor.
As in the case of the Danes, the Norwegians' earliest standards of measure can be derived from their ship burials.The 60-Norwegian-feet-long Kvalsund ship (18.8 m; 61.8 ft) was built ca. 700 AD and differs from the Danish boats less than it does from the Oseberg, Gokstad and Tune ships which all date from ca. 800 AD.