365 HYDROGRAPHIC MANUAL PaGE 282 



The conditions imder which an area breaks must be noted, at what stage of the 

 tide, and under what conditions of the sea. The distance at which the break is usually 

 visible should also be noted. 



Where sunken rocks exist inside a generally foul area they may be symbolized 

 without location so long as the outline of the foul area is accurately located (see 



also 367). 



365. Wrecks and Obstructions 



All wrecks and obstructions not afloat should be located and as complete informa- 

 tion as practicable furnished. \A%ether the wreck is totally submerged, visible at all 

 stages of the tide, or visible at some stage of the tide, should be stated and any visible 

 parts of the wreck should be described. 



When large pieces of floating wreckage, logs, or other debris, menacing to naviga- 

 tion, are sighted in areas where such obstructions are not commonly encountered, they 

 should be reported immecjiately by radio to the Commander of the nearest United 

 States Coast Guard District. 



Sunken wrecks should be treated as dangers or shoals and the same information 

 should be obtained relative to them. The least depth on a wreck is practically impos- 

 sible to determine without dragging the area because of the probable existence of masts 

 or other parts of the wreck which one cannot expect to find by ordinary soundings. 



366. Examination of Shoals 



An examination shall be made to determme the least depths on all dangers to navi- 

 gation and important shoals in the project area. The regular system of sounding lines 

 in the area or a more closely spaced system for development, may locate the position of 

 a shoal within definite limits, but only in rare instances will the least depth be found in 

 this manner, particularly where the area is rocky. The least depth must be found by 

 an intense examination of the limited area in which the shoal is known to exist. This 

 may be accomplished in any one of several ways. 



Wliere the bottom is visible there is no particular difficulty in finding the least 

 depth. If a shoal is small in area and is visible, the sounding boat can be placed above 

 it and the leadline watched to ensure that a sounding is obtained on the peak of the 

 shoal. Wliere the bottom is not visible, the least depth may be determined either by a 

 system of closely spaced lines over the shoal, by wire drag, hj feeling with the leadline, 

 or by drift soundings. 



Where the investigation for least depth consists of a system of closely spaced lines 

 controlled by visual fixes all of the soundings should be recorded; but for drift sound- 

 ings and feeling with the leadline, only the least depth found and its position need be 

 recorded (see 3666). As this is a detached position a check angle must be taken, if 

 practicable. 



The character of the bottom on each important shoal must also be determined and 

 recorded. 



The examination of the shoals discovered should progress with the systematic 

 survey of the area and all shoals or indications found during a season must be examined 

 before the close of the season. Such work should not be postponed until near the end of 

 the season when stormy weather or other circumstances may prevent the comi k-tion 

 of all the work planned. 



