30 



HYDROGRAPHIC MANUAL 



wise be considered fool-hardy. In such cases 

 the Commanding Officer must exercise the 

 nicest discrimination, but both he and his 

 officers must beware of overconfidence. 



In surveying an area where a known danger 

 exists, or where one has been reported or is 

 suspected of existing, certain definite pre- 

 cautions are necessary. Because of the wide 

 variety of conditions which may be en- 

 countered, no all-inclusive rules of safety can 

 be drawn. The following general rules should 

 be followed when approaching a known or 

 suspected danger: 



(a) If practicable, the dangerous area 

 shall first be surveyed from a launch to find 

 and locate the danger and to survey an area 

 around it with which a junction can be made 

 in safety from the survey ship. 



(b) The Commanding Officer, before ap- 

 proaching the area, shall make a study of 

 all available data. 



(c) The Commanding Officer shall be on 

 the bridge, and shall take charge of the 

 navigation of the ship. 



(d) The ship shall proceed at slow speed. 



(e) An officer shall be on the lookout in 

 addition to any members of the crew. 



(f) Information on reported dangers may 

 be incorrect as to location, depth, and number 

 of submerged obstacles. 



2-31 International code flags. — A com- 

 plete set of International Code flags shall be 

 carried for navigational purposes, being dis- 

 played as the occasions require. 



A card illustrating the various flags shall 

 be kept in the pilothouse in a convenient 

 location. 



Ships and auxiliary vessels engaged in 

 hydrographic surveying underway in the day- 

 time should display suitable International 

 Code signals in areas where there may be 

 considerable foreign ship traffic. The appro- 

 priate International Code signals are : 



"HD," Signifying "I am engaged in 



submarine work, you should keep clear 



of me." 



"HF," Signifying "I (We) have a sweep 



out, you should keep clear of it." 



In addition to the above signals, the code 



flags most frequently used by ships of the 



Coast and Geodetic Survey are the red flag 

 to indicate that explosives or highly inflam- 

 mable fuels are being loaded, and those com- 

 posed of groups used in recalling launch and 

 shore parties. 



2-32 Inland and international rules. — 

 The Inland and International Rules of the 

 Road authorize or require a survey vessel to 

 display prescribed recognition signals. The 

 lights or shapes shall be displayed in ac- 

 cordance with the rules as follows : 



(a) Section 80.33 Pilot Rules for Inland 

 Waters. — By day a surveying vessel of the 

 Coast and Geodetic Survey, under way and 

 employed in hydrographic surveying, may 

 carry in a vertical line, one over the other 

 not less than 6 feet apart where they can 

 best be seen, three shapes not less than 2 

 feet in diameter of which the highest and 

 lowest shall be globular in shape and green 

 in color and the middle one diamond in shape 

 and white. 



Vessels of the Coast and Geodetic Survey 

 shall carry the above-prescribed marks while 

 actually engaged in hydrographic surveying 

 and under way, including drag work. 

 Launches and other boats shall carry the 

 prescribed marks when necessary. 



It must be distinctly understood that these 

 special signals serve only to indicate the 

 nature of the work upon which the vessel is 

 engaged and in no way give the surveying 

 vessel the right-of-way over other vessels or 

 obviate the necessity for a strict observance 

 of the rules for preventing collisions. 



By night a surveying vessel of the Coast 

 and Geodetic Survey, under way and em- 

 ployed in hydrographic surveying, shall carry 

 the regular lights prescribed by the rules of 

 the road. 



A vessel of the Coast and Geodetic Survey, 

 when at anchor in a fairway on surveying 

 operations, shall display from the mast during 

 the daytime two black balls in a vertical line 

 and 6 feet apart. At night two red lights 

 shall be displayed in the same manner. In 

 the case of a small vessel the distance be- 

 tween the balls and between the lights may 

 be ref'uced to three feet if necessary. 



Such vessels, when at anchor in a fairway 



