Case Vffl 



TO DETERMINE COURSE AND SPEED OF GUIDE FROM TWO SETS OF SIMULTANEOUSLY OBSERVED RANGES 



AND BEARINGS 



GIVEN: OWN COURSE AND SPEED, TWO SETS OF SIMULTANEOUSLY OBSERVED RANGES AND BEAR- 

 INGS OF GUIDE FROM THE MANEUVERING UNIT, AND TIME INTERVAL BETWEEN OBSERVATIONS. 



TO DETERMINE: COURSE AND SPEED OF GUIDE, AND POSITION OF MANEUVERING UNIT RELATIVE 

 TO GUIDE AT ANY SUBSEQUENT TIME. 



Example. — A destroyer rejoining a formation at a geographical point, after being on detached duty, is now on course 

 026°, speed 25.0 knots. The course and speed of the formation have not been signalled, since radio silence is in effect and the 

 use of visual signals is restricted. At 1600 the first vessel in the formation is sighted and a simultaneous range of 29,000 yards 

 and bearing of 007° obtained. This vessel is later identified as the Formation Guide, and at 1617 another observation is ob- 

 tained, giving range of 20,000 yards and bearing of 014°. The commanding officer of the destroyer decides to maintain present 

 course and speed until 1630, at which time he would head for this proper position in the formation. 



Required. — (a) Course and speed of the Guide, (b) Relative position of the destroyer at 1630. (See fig. 11.) 



Procedure. — Plot the Guide at G and the relative positions of the destroyer at 1600 and 1617 at A and D 2 respectively. 

 Measure the Relative Distance D\ . . . . D 2 . 



Using the Logarithmic Scale, the time between observations, and the Relative Distance, determine the Relative Speed. 



Draw the destroyer's vector e . . . . d, and transfer the slope Di . . . . D 2 to d. Using the Relative Speed found above 

 measure it on this slope, locating g. e .... g is the vector representing the course and speed of the Guide. 



To locate the position of the destroyer relative to the Guide at 1630, continue the Relative Movement Line beyond D 2 

 and use the Logarithmic Scale. The estimated position D 3 may be plotted from either Di or D 2 , depending upon whether 30 or 

 13 minutes are used for length of time on Relative Movement Line. 



Answer. — (a) Course 066°, speed 14.7 knots, (b) 13,600 yards, bearing 206° from Guide. 



NOTE. — The vessel which is taking the bearings and ranges may be designated as the Guide in some problems, in which case it should be 

 located first, and the other vessel plotted from the Guide's position. The solution is similar. 



18 



