Hydrographic Manual 



CHAPTER 1. PRELIMINARY 

 11. GENERAL STATEMENT 



Every important maritime nation surveys its coasts and territorial waters and 

 publishes nautical charts of the world sea routes. Nothing has been of more importance 

 in the establishment and development of a merchant marine than the productio'n of 

 nautical charts, which in turn must be based on accurate hydrographic surveys. A& 

 long as sea-borne commerce continues, hydrographic surveys will be required. 



Few of the coasts of the world have been adequately charted and the depths in 

 most of the water areas are still only imperfectly known. Furthermore, even where 

 adequate charts have once been made, man and nature are constantly changing the 

 depths of the water, the coastline, and the adjacent structures, so that frequent revision 

 surveys are required. Moreover, the increased draft of vessels and the importance of 

 maintaining schedules call for more critical surveys, and render charts and surveys 

 obsolete which once were considered adequate. 



Formerly, no extensive survey of the bottom configuration was made except in 

 the lesser depths near the shore, in channels, and in the vicinity of shoals. T-oday, a 

 detailed hydrographic survey is required regardless of the depth, for the bottom con- 

 figuration where accurately indicated on a chart may provide a simple means of locating^ 

 a vessel underway from a series of soundings taken with an echo-sounding instrument. 

 The same instrument allows the detailed surveys to be made expeditiously, it being no 

 longer necessary to stop the ship to obtain the deeper soundings. 



111. Introduction 



The first hydrographic information available for the use of mariners was in the 

 form of written descriptions of the coasts along which they sailed. These were crude 

 beginnings of what we now know as Sailing Directions, or Coast Pilots. At first, 

 they probably consisted of the merest details of headlands. As the early seafarers 

 ventured farther from home, it was found desirable also to preserve information con- 

 cerning the channels and harbors, and the dangers to be avoided along such routes. 



These descriptions were prunarily for the safety of the mariner and were first 

 prepared by the mariners themselves, who passed from one to another the details 

 of the routes to be followed and the places visited. They may have been accompanied 

 by crude sketches and if so, these were the first maps prepared especially for the use 

 of seafarers. That they were of utilitarian value onty, may account for the fact that 

 they were not permanently preserved. 



The first marine charts of which there is actual record are those constructed by 

 Marinus of Tyre during the second century. He was followed by the Egyptian 

 Ptolemy who made use of his charts. Ptolemy published a list of places to which 



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