17 HYDROGRAPHIC MANUAL PaGE 56 



always menaces to surface navigation. Similar continental or insular shelf features of greater depth 

 are usually termed banks.) 



SPUR. — A prolongation of a land ridge onto or across the continental or insular shelf; or any 

 minor submerged ridge; or a submerged ridge of lower elevation projecting or radiating from a larger 

 and higher feature. 



17. OPERATIONS BEYOND PROJECT LIMITS 



Survey vessels when proceeding to or from their project areas should take every 

 opportunity to verify the published charts and coast pilot information along their route, 

 in ports at which they may call, and particularly in areas immediately adjacent to 

 their project. Echo sounding has made it possible to obtain soundings along the 

 route without material delay to the vessel. 



171. Sounding en Route 



Advantage should be taken of the transit of vessels to obtain information in blank 

 or insufficiently sounded areas on the charts. It is frequently possible to make a 

 slight deviation from the direct course between two places in order to pass over such 

 areas. With echo sounding one line may be run across the area without delay in passage. 



If the area is offshore and out of sight of land the voyage should be planned, if 

 practicable, to arrive at the area shortly after sunrise so that an adequate astronomic 

 fix may be obtained shortly before arrival. 



Soundings obtained en route may be plotted on a copy of the largest-scale chart 

 of the area, on which should also be shown the lines of position, if astronomic obser- 

 vations have been obtained. The chart should be forwarded to the Washington 

 Office with a report discussing in full the circumstances and giving complete data 

 regarding the control used. 



172. Reported Shoals 



Each survey vessel should investigate any reported shoals or dangers to navigation 

 along a route, especially those marked ED (existence doubtful) or PD (position doubtful) 

 on the charts. Circumstances will determine to what extent deviation from a pre- 

 arranged route is justifiable in a given case. Such shoals or dangers as lie immediately 

 adjacent to the project area should be thoroughly examined as opportunity affords. 

 The project instructions will specify the type of examination to be made for those areas 

 known to require special investigation. 



There may be reported locally to the Chief of Party dangers to navigation con- 

 sisting of rocks, reefs, shoals, or sunken wrecks either not charted or incorrectly charted 

 and each of these should be investigated if the information is believed reliable enough 

 to warrant it. Experience has shown that many such reports are untrustworthy 

 either because they are based on discolored water or floating debris having been 

 sighted or because the position reported is far from the true one. It is often very 

 difficult to prove or disprove the existence of a reported danger, especially if it is 

 out of sight of land. A preliminary investigation may only tend to prove or disprove 

 its existence, requiring subsequent arrangements for a more thorough examination. 

 In such cases the facts should be reported to the Washington Office by radio and 

 instructions requested. 



To make a thorough investigation to prove or disprove a reported danger out of 

 sight of land, it is almost essential to use one or more survey buoys to ensure 

 adequate coverage of the area (see 2535 and 2571). Survey buoys can now be anchored 



