Page 41 preliminaky 1551 



Landmarks on charts are for the aid of the mariner navigating the adjacent waters, 

 and the objects recommended for this pm-pose should be selected with this fact in mind. 

 They should be such as could be used for control objects by a hydrographic survey 

 party, except that only the most prominent of these are of value. 



The selection of objects should be made as the offshore water area is sounded, 

 since from this viewpoint an adequate selection is relatively easy. When the selection 

 is made by a survey party based on shore or engaged in land operations, extreme care 

 is necessary in making a selection. Objects not visible from the water should seldom be 

 reported; if practicable, an inspection should be made from the water area to determine 

 the value of the ob j ects reported . The report should state whether or not this inspection 

 has been made. 



The report on landmarks should cover the entire area surveyed during the season 

 and should be based on an over-all study of the area. Form 567 should not be submitted 

 for each hydrographic or topographic survey. Where there is a plethora of landmarks 

 in any given area only those of special importance or prominence should be reported. 

 By contrast, however, objects of lesser prominence may become important in an area 

 where there is a paucity of landmarks. It is desirable that there be a proper distribu- 

 tion of landmarks reported rather than a concentration of a large number in a small area. 



Usually landmarks important enough to be listed in the report will have been 

 located by triangulation or topography during the progress of the survey. For land- 

 marks not so located, in areas covered by the planimetric maps of this Bureau, it will 

 usually be practicable to locate them with sufficient accuracy by reference measurements 

 to identifiable detail on the maps. In one test of this method, seven landmarks were 

 located which were subsequently located by triangulation. A comparison of the 

 resulting positions gave an average difference of location of only IK meters, with the 

 largest discrepancy 4 meters. 



A report of landmarks to be deleted from the charts because no longer existent 

 or not prominent is also important, and should be submitted on Form 567 at the end 

 of the season. A systematic check should be made of the charted landmarks as the 

 survey progresses. 



Instructions for the preparation of Form 567 are given in 8534. 



1551. Objects for Use in Locating Aids to Navigation 



The personnel of United States Coast Guard tenders use the three-point fix method, 

 wherever possible, to locate floating aids to navigation and to replace them on their 

 stations. For their use in this work a special chart shall be prepared by each hydro- 

 graphic party on which shall be shown the objects, natural or artificial, best suited for 

 this purpose (see 8533). 



During the survey each floating aid to navigation shall be visited for the purpose 

 of selecting by inspection the most suitable objects. These need not be restricted to 

 landmarks recommended for charting; if there is an insufficiency of these in the most 

 appropriate locations, they should be supplemented by less prominent objects, visible 

 from the respective aids, and located specifically for this purpose. Permanent objects 

 not hkely to be destroyed or moved shall be selected. The use of beacons, range marks, 

 targets, etc., should be avoided. If three suitable objects cannot be seen, two objects 

 should be noted, if practicable, to which bearings can be measured. 



