1. GENERAL REQUIREMENTS 15 



ure from true depth due to the method of the work progresses, a careful study of the 

 sounding, or to a fault in the measuring soundings and curves will disclose where ad- 

 apparatus, and for the height of the tide ditional development is required and where 

 above or below the plane of reference at the errors have been made which must be in- 

 time of sounding (see 5-100 to 123). vestigated. No single requirement for the 



Corrections shall be entered in the sound- spacing of depth curves can be prescribed 



ing volume in the same unit in which the to apply to all regions (see 5-64, 65). The 



soundings have been recorded. Parts of units curves should be spaced closely enough to 



shall be entered in decimals — fractions depict the submarine relief completely and 



shall not be used. accurately. A good general rule is that the 



A variety of corrections may be required depth curves on boat sheets should be drawn 



including any or all of the following: draft, so far as practicable at the following 



variation of the initial from the adopted intervals: 



index, settlement and squat, velocity (tem- (a) At 1-fathom intervals to 10 fathoms; 



perature, salinity, and pressure), tide, in- (b) At 5-fathom intervals between 10 and 



correct speed of echo-sounder operation, 50 fathoms ; 



phase, incorrect radius of rotation of the (c) At 10-fathom intervals between 50 



stylus arm on 808 recorders and misalign- and 100 fathoms; 



ment of paper. All data necessary to apply (d) At 25-fathom intervals in depths 



final corrections to soundings shall be accu- greater than 100 fathoms, 



mulated as field work progresses. The standard depth curves required on 



Soundings shall be reduced to the plane smooth sheets should always be inked on the 



of reference from predicted tide curves or boat sheet in the colors prescribed for smooth 



from observed tides and significant phase sheets (Table 3). Supplementary curves 



or initial corrections applied when the sound- may be inked if necessary to emphasize the 



ings are inked on the boat sheet. Unless the relief. 



soundings on the boat sheet are approxi- ^able 3.— Standard depth curves 



mately correct, poor crossings may not be -= ■ 



j_f^^i._j Curve in Curve in To be inked 



UeietieU. fathoms feet in 



1-40 Boat sheet soundings. — Soundings o (Plane of reference) Orange. 



shall be plotted on the boat sheet with black i 6 p'^h'^"' 



India ink each day as hydrography progres- 3 ^g ........ Blue. 



ses. Although expert penmanship is not re- 5 30 Red. 



quired, the soundings shall be of uniform 20 120 ........ Blue. 



size and clearly legible (see 5-63). The least 30 180 Violet. 



depth on shoals and banks should be inked ^q 3qq . . . . Red^" 



in slightly laiger and heavier figures. A note 100 6O0 Green. 



and leader may be used if desired. Rock sym- ^qq ~ Violet^ 



bols shall not be obliterated by soundings 400 - Green. 



or other symbols. ^^0° I ; ; ; ; ; ; ; ; ff^^^ 



Bromide copies of boat sheets are used 2,000 - Orange. 



, , i.- 1 I, 4. • J t 3,000 - Violet. 



to correct nautical charts in advance of re- _| 



ceipt of the smooth sheets. It is therefore n,. , , o 1 » i -j «. _. 



^ Table 4. — Supplemental depth curves 



important that the soundings and other data — 



on the boat sheet shall not be ambiguous on 1^ 3 Violet. 



these reproductions. 4 24 Orange. 



6 36 Green. 



1-41 Depth curves on boat sheets.— The S!J ^oS ]5'"®' 



, , , , , 70 420 Green. 



depth curves should be drawn on the boat go 480 Red. 



sheet in pencil by the hydrographer and, as ^0 ^^^ Violet. 



