Page 297 hydrography 382 



shore specifically for this purpose. From each of these fixes, sextant cuts (preferably 

 three to each point) may be taken and rangefinder distances measured to any recog- 

 nizable features along the shoreline, the intermediate shoreline being sketched in. 

 The necessary angles and data can often be conveniently obtained in connection with 

 the hydrography by stopping the boat temporarily at the inshore end of each line of 

 soundings. The results of course are inadequate for charting on a large scale, but on 

 small scales where minor detail is usually generalized the results will give a reasonably 

 accurate portrayal. 



In areas such as the Aleutian Islands, Alaska, heavy ocean swells may sometimes 

 prevent the topographic party from landing along certain parts of the coastline. If, 

 toward the end of the season, an inshore hydrographic survey has been completed, 

 but the corresponding topographic survey has not, the shoreline should then be sketched 

 from a launch for temporary use in charting. The topographer or the hydrographer 

 takes the boat sheet in the launch and cruises off the shore at an appropriate distance 

 where he can locate his position by strong three-point fixes from the hydrographic 

 stations previously located by cuts and which are plotted on the boat sheet. Additional 

 points on shore are then cut in from the launch, and the shoreline between the points 

 carefully sketched. Such shoreline shall be shown on the boat sheet by a dash line 

 inked in black. 



This method of locating the shoreline and offshore topographic details should be 

 used only as a last resort and then only for areas of relative unimportance. An ade- 

 quate report shall be made as to why the topographic survey was not accomplished, and 

 a statement shall be included as to the probable accuracy of the result by these substitute 

 methods. 



382. Form Lines From the Ship 



Form lines to represent the topographic relief are an important part of a chart, for in 

 piloting the mariner determines his position from those objects he can identify. Conse- 

 quently, when surveying in an uncharted area, the Chief of Party should see that topo- 

 graphic features of value to the mariner are located as far inland as practicable. This is 

 particularly applicable to the rugged coastal areas of the United States, the Philippines, 

 and Alaska where many conspicuous moimtains, hills, and ridges bordering the shore- 

 line lie beyond the limits of the standard 1:10,000 and 1:20,000 scale topographic sheets. 



During an ordinary topographic survey of the shoreline, the topographer is fre- 

 quently limited to cuts to unimportant points on the slopes of minor hills and ridges 

 which rise abruptly from the shoreline. In an efl'ort to supplement the planetable 

 topography with sextant cuts from offshore, it is often found that the desired features 

 lie beyond the inshore limits of the sheets, or that the positions from which satisfactory 

 cuts to such features must be obtained are beyond the offshore limits of the sheets. 



Sheets for form lines only, constructed at scales one-half to one-fourth those of the 

 regular topographic sheets, can usually be laid out so that their limits will include all 

 topographic features which are of greatest value to the navigator and at the same time 

 include the offshore water area from which satisfactory cuts may be obtained. 



Form lining from the ship can be accomplished simultaneously with the ship 

 hydrography and without any interference with it. The only additional personnel 

 required are sextant observers, and in most instances one is sufficient. The cuts 

 shoidd be recorded in the regular Sounding Record (see 248) with their respective 

 hydrographic position numbers for plotting at a later date. It is not necessary to 

 stop the vessel to obtain sextant cuts, but advantage should be taken of any stops 

 (for vertical casts, serial temperatures, lowering or hoisting launches, etc.) to obtain 



