18 (Change 1) 



HYDROGRAPHIC MANUAL 



(e) Set and drift observations as deter- 

 mined by difference in position between be- 

 ginning and end of observations, if prac- 

 ticable. 



(f) Weather observations (see H.O. Pub- 

 lication 607, Figure C-8). 



1—49 Bathythermograph (BT) observa- 

 tions. — When instructed to make bathythermo- 

 graph observations, lowerings should be made 

 at intervals of not more than 2 hours. Data 

 ivom BT slides should be processed in accord- 

 ance with procedures outlined in project instruc- 

 tions. General instructions for use of BT's 

 are contained in H.O. Publication 607. 



1-50 Aids to navigation. — All fixed aids 

 to navigation established by the United 

 States Coast Guard should be located by 

 triangulation. A substitute method may be 

 used if necessary, but the determination 

 shall be such that no appreciable error will 

 result. The azimuth of range lines shall be 

 determined by triangulation if practicable. 



The positions of and depths at all floating 

 aids to navigation in the project area shall 

 be determined by the hydrographic party. 

 Floating aids should be located by sextant 

 fixes, not cuts, with one or more check an- 

 gles, and shall be fully described. 



If a floating aid is found to be off station 

 as shown on the largest scale chart of the 

 area, the fact should be promptly reported 

 to the Commander of the nearest Coast 

 Guard District. If the aid is off station to 

 an extent that a danger to navigation exists, 

 the facts should be reported by dispatch. 

 Any recommendations, based on new hydro- 

 graphic surveys, for additional aids or for 

 more desirable locations of existing aids, 

 should be reported to the Coast Guard in 

 writing as soon as practicable, with a photo- 

 stat or tracing of the boat sheet. Copies of 

 all correspondence with the Coast Guard 

 shall be furnished the Washington Office 

 (see 5-80). 



1-51 Dangers to navigation. — All shoals, 

 rocks, wrecks, etc., discovered, that are con- 

 sidered dangers to navigation, shall be re- 



ported immediately by radio, telegraph, or 

 telephone to the Commander of the nearest 

 U.S. Coast Guard District and to the Coast 

 and Geodetic Survey District Office (see 5-72 

 and 7-23). A copy of the message shall be 

 forwarded to the Washington office with a 

 tracing from the boat sheet or chart showing 

 the exact location of the danger. 



1-52 Wire-drag investigations. — In many 

 cases time can be saved by use of a wire 

 drag to investigate indications of submerged 

 dangers (see 5-124). When reported dan- 

 gers or obstructions cannot be found by 

 standard survey methods, the surrounding 

 area should be wire dragged to prove or dis- 

 prove their existence. Evidence to support 

 a recommendation to delete charted dangers 

 or obstructions must be conclusive. All wire- 

 drag operations shall be conducted in ac- 

 cordance with the requirements of Publica- 

 tion No. 20-1, Wire Drag Manual. 



1-53 Coast Pilot report. — All hydro- 

 graphic field parties shall collect Coast Pilot 

 information and furnish at the end of the 

 season a special report on this subject for 

 use in the revision of the Coast Pilot of the 

 area (see 2-36). The report should be sub- 

 mitted in duplicate and should be a compila- 

 tion of all such data collected by each unit 

 of the survey party. If the information in 

 the published Coast Pilots is correct and ade- 

 quate, a statement to this effect should be 

 included in the report. 



1-54 Geographic names. — The hydro- 

 graphic surveys should be the authority for 

 all geographic names seaward from the high- 

 water line, including the names of all water 

 features such as channels, sloughs, rivers, 

 inlets, bays; and those of the reefs, rocks, 

 banks, and shoals therein; and all small 

 islands and the names of geographic fea- 

 tures thereon. It is particularly important 

 that geographic names be correct not only 

 as to name, but also as to spelling and ap- 

 plication. Charted names and those in the 

 Coast Pilots should be checked against local 



