Page 677 the smooth sheet 735 



The continued use of the beam compass at the R.A.R. stations tends to enlarge the 

 station holes. To avoid this a small circular piece of thin celluloid is temporarily placed 

 over each station with Scotch tape, so that the compass point rests on the celluloid 

 instead of on the paper. Where this is done the pricked point in the celluloid must be 

 precisely over the plotted position on the smooth sheet. Pencil lines should be drawn 

 at right angles through the plotted position on the smooth sheet, by which the celluloid, 

 on which similar lines at right angles have been drawn or finely etched, may be correctly 

 superposed. If only a few distance circles are to be drawn from any one station the 

 celluloid may be dispensed with, if caution is taken to avoid an excessive downward 

 pressure on the beam compass. 



Two R.A.R. control stations are frequently used at locations very close to one 

 another. Confusion would result if concentric distance circles were drawn from both 

 of these as origins. Instead, the distance circles are drawn from that station from which 

 the larger percentage of R.A.R. distances was obtained during the survey. The method 

 of plotting in such cases is explained in 7631. 



There will be occasional cases where an R.A.R. station used for control is beyond 

 the limits of the sheet. If such a station is within reach of a beam compass, it may 

 be plotted by using a computed distance and direction from a latitude and longitude 

 intersection on the projection. A specially long beam compass may be required for 

 drawing the distance circles (see 3741cl). 



Distance circles involving radii too long to be drawn with a beam compass may 

 be constructed by computing the rectangular coordinates of points on the circles and 

 drawing the circles by using standard curves. The formulas for computation are the 

 same as for constructing "circle" sheets by the computation method except that the 

 origin of coordinates is taken as the intersection of two distance cu-cles on the sheet, 

 the F-axis being the azimuth from the intersection to an R.A.R. station and the A''-axis 

 being normal thereto at the same point. (See 3741c2.) 



After the distance circles have been drawn on the smooth sheet and the other con- 

 trol stations plotted and checked, the projection lines are inked (see 7323). Control 

 station names in the water area must be left in pencil for subsequent inking (see 7443). 



735. Plotting Large-Scale Offshore Surveys 



Large-scale offshore surveys using three-point fix control cannot usually be made 

 or plotted with the degree of accuracy required, if conventional methods of plotting 

 are used — that is, with a three-arm protractor. Instead, the "circle" sheet method is 

 used in which the observed angles are plotted by means of their loci, systems of which 

 have been drawn in advance on the boat sheet or smooth sheet. A full discussion of 

 this method of surveying and, of the method to be used in preparing such sheets is given 

 in section 37. The smooth plotter should famiharize himself thoroughly with the 

 method before beginning work on such a smooth sheet. 



After the arcs have been plotted and verified, they should be mked in blue usuig 

 a fine light line similar to that used for R.A.R. distance circles (see 7341). The arcs 

 should be identified by inking the degrees and min utes in the same color near the ends 

 of the arcs. It is unnecessary and undesirable to ink all the arcs used in protracting 



