5. HYDROGRAPHY 



127 



development of echo sounding equipment are . 

 considered inadequate for modern charting 

 purposes. Some areas are subject to change 

 by storms, tidal currents, or engineering de- 

 velopments and must be resurveyed peri- 

 odically. These are revision surveys and 

 instructions may require a complete basic 

 survey of the area, or limited surveys in 

 areas of danger (see 5-125 and 127). 



5—3 Survey operations. — Instructions for 

 a survey project (see 2-5 to 13) will be 

 issued and the necessary data furnished suffi- 

 ciently in advance of field work to permit 

 formulation of a general plan of operation 

 (see 2-15). Plans for day to day operations 

 must be fitted into the general plan as cir- 

 cumstances dictate in order that operations 

 can be carried on smoothly and efficiently. 

 All survey operations required in an area 

 should be completed as the work progresses. 

 Miscellaneous operations such as magnetic 

 observations, development of shoal indica- 

 tions, compilation of coast Pilot notes, etc., 

 should be kept up to date. 



A hydrographic survey has not served its 

 ultimate purpose until it has been incor- 

 porated in a published nautical chart. The 

 data accumulated should be processed as 

 rapidly as possible. Periods of inclement 

 weather should be devoted to processing, and, 

 when a considerable volume of unprocessed 

 records have been accumulated, it is advis- 

 able to use periods of marginal weather for 

 this purpose (see 5-100 to 123 and Chap- 

 ter 6). 



5-4 The boat sheet. — The boat sheet is 

 the hydrographer's work sheet used in the 

 field to plot the details of a survey while it 

 is in progress. On it is laid out a proposed 

 plan of sounding lines spaced in accordance 

 with instructions. Fixed position are plotted 

 as they are observed. Soundings, reduced 

 for tide or other significant corrections, are 

 inked on the sheet and depth curves drawn. 

 Daily examination of the results will dis- 

 close indications of shoals which must be 

 examined and where additional lines are re- 

 quired to comply with project instructions 

 or to define depth curves more adequately. 



The boat sheet is similar to the smooth 

 sheet (see Chapter 6) but may be less ac- 

 curate and generally not so neatly done, but 

 all information plotted on it should be as 

 accurate as circumstances permit and clearly 

 legible. No important information should be 

 omitted. Temporary or permanent notes may 

 be written in margins or on land areas. 



A photographic copy of the boat sheet will 

 be used to apply corrections, if necessary, 

 to the chart of the area. The boat sheet 

 will be used by the smooth plotter and will 

 be referred to many times as the smooth 

 sheet is verified and reviewed. 



5-5 Boat-smooth sheet. — When surveys 

 are being made in off'shore areas and elec- 

 tronic control is used, the boat-smooth sheet 

 method of plotting the hydrography can be 

 used to advantage, especially where very lit- 

 tle development is required. When this 

 method is used, the instructions for smooth 

 plotting contained in Chapter 6 shall be fol- 

 lowed with one exception: corrections to ob- 

 served distances to the fixed stations shall 

 be determined by careful calibration as de- 

 scribed in Chapter 3, and the corrections 

 applied on the abstract sheets as the posi- 

 tions are plotted. The records or descriptive 

 report shall indicate any plottable differences 

 between the final corrections and those used 

 to plot the hydrography. 



A transparent cover with matching pro- 

 jection ticks shall be placed over the smooth 

 sheet while positions are being plotted. 

 Tracing cloth or a thin sheet of grained 

 mylar may be used for this purpose. As the 

 positions are plotted they shall be pricked 

 through the cover sheet to the smooth sheet. 

 The cover sheet shall serve as a boat sheet 

 and all position numbers and soundings shall 

 be inked on it in the usual manner. At the 

 end of the day or at other convenient times, 

 the cover sheet is lifted and the positions 

 on the smooth sheet connected by fine pencil 

 lines. The position numbers are carefully 

 inked in accordance with smooth sheet prac- 

 tices (see 1-10 and 6-45) . 



After all corrections have been applied the 

 reduced soundings are plotted on the smooth 

 sheet in pencil. Ordinarily the soundings are 



