HYDROGRAPHIC MANUAL 



which must never be exceeded under any cir- 

 cumstances, is 42 by 60 inches. 



1-9 Boat sheet paper. — Boat sheets shall 

 be prepared on first-quality white drawing 

 paper mounted on muslin, or on aluminum- 

 mounted paper furnished by the Washington 

 Office. The muslin mounted sheets should 

 be well seasoned before the projections are 

 drawn. 



1-10 Boat-smooth sheet procedure. — 



Hydrographic parties are authorized and en- 

 couraged to use a combination boat and 

 smooth sheet where practicable. This 

 method of field plotting will avoid the neces- 

 sity for replotting the positions and thus 

 reduce the time and effort required to obtain 

 a smooth copy of the survey (see 5-5 and 

 6-45). 



When this method is used for an electroni- 

 cally controlled survey the final corrections, 

 as far as is practicable, shall be applied to 

 the measured distances before they are 

 plotted. The records or descriptive report 

 shall show any plottable discrepancies be- 

 tween values used to plot the positions and 

 the final corrected values of the measured 

 distances. A transparent cover shall be 

 placed over the sheet during position plotting. 



All procedures other than position plot- 

 ting shall conform with instructions for 

 smooth plotting a hydrographic survey. (See 

 Chapter 6.) 



1-1 1 Projections. — The Bureau has adopt- 

 ed for all surveys a projection known as the 

 Coast and Geodetic Survey polyconic pro- 

 jection and all surveys must be plotted on 

 this projection. North shall always be con- 

 sidered the top of the sheet, whether or not 

 the projection lines are parallel to the edges 

 of the sheet. In plotting and inking boat 



sheets all lettering and numerals of any kind 

 shall be so lettered as to be read from the 

 south. All boat sheet projections shall be 

 constructed in the field unless the project 

 instructions specifically state that they will 

 be furnished by the Washington Office. 



1-12 Construction of projection. — The 



construction of a polyconic projection is a 

 simple problem, but extreme accuracy and 

 care are required. Instructions and data for 

 construction of a projection are contained 

 in Special Publication No. 5, The Polyconic 

 Projection Tables. The projection must be 

 constructed and checked in one continuous 

 operation and as rapidly as possible and con- 

 sistent with accuracy required (see 5-6 and 

 7). The sheet should not be exposed to the 

 direct rays of the sun, and the projection 

 should be made during a period of weather 

 when conditions of temperature and humid- 

 ity are stable and about average for the con- 

 ditions under which the sheet is to be used. 



The projection must be checked the same 

 day it is constructed and immediately fol- 

 lowing construction. Rubber stamp No. 42, 

 Hydrographic Survey, shall be impressed at 

 an appropriate place near the right edge of 

 the sheet. Entries should be made in all the 

 applicable spaces of the stamp. 



The projection intervals between the me- 

 ridians and parallels to be shown on a sur- 

 vey sheet depend on the scale used and shall 

 be as specified in Table 1. 

 The projection is constructed in pencil. It 

 must be verified and all control stations plot- 

 ted, by dms and dps, and checked while the 

 lines are in pencil. The projection lines 

 should then be inked as fine solid black lines 

 0.15 mm. in width extending entirely across 

 the sheet. 



Table 1. — Projection line intei-vals for various .scales 



Scale of Survey /'rojiclion l.hu IiitrTval 



1:2,000 and larger Every 5 seconds. 



1:2,001 to 1:.3,000 Every 10 seconds. 



1:3,001 to :■: 6,000 Every 15 seconds. 



1:6,001 to 1:12,500 Every 30 seconds. 



1:12,501 to 1:25,000 Every minute. 



1:25,001 to 1:60,000 Every even minute. 



1:60,001 to 1:125,000 EverV 5th minute. 



1:125,001 to 1:2.50,000 Every 10th minute. 



