





CaseXm 



GIVEN: COURSE AND SPEED OF GUIDE, INITIAL POSITION AND SPEED RESTRICTIONS OF MANEU- 

 VERING UNIT, AND RANGE TO BE REACHED IN MINIMUM TIME. 



TO DETERMINE: COURSE OF MANEUVERING UNIT AND TIME TO REACH SPECIFIED RANGE. 



Example. — A destroyer now stationed 10.0 miles 80° on the starboard bow of the Fleet Guide receives orders to close to 

 4,000 yards from the Guide as quickly as possible. The destroyer is capable of making 24.0 knots. Fleet course is 020°, fleet 

 speed 15.0 knots. 



Required. — (a) Course of the destroyer, (b) Time to reach 4,000-yard (2.0 mile) range, (c) Relative bearing of D 

 from G when range is reached. (See fig. 17.) 



Procedure. — Plot the Guide at any convenient point G, and locate the initial position of the destroyer, bearing 080° 

 relative or 100° true from G. Mark this point D. 



From G, in a direction the reverse of the Guide's course, lay out G .... X equal to P ee ° XRange to be reached 



Speed of D 



or 1.25 miles. 



About G draw a circle with 2.0 mile radius. Join D .... X, cutting the 2.0 mile circle at Y. D . . . . Y is the line of 

 Relative Movement of D. 



Lay out the Guide's vector e . . . . g. Transfer the slope D .... Y .... X to g, intersecting the 24.0-knot speed 

 circle at d. e . . . . d represents the course and speed of D. 



The time to arrive at the specified range is found from the Logarithmic Scale, using the Relative Distance D .... Y 

 and the Relative Speed g . . . . d. 



Answer. — (a) Course 310°. (b) 21.3 minutes, (c) 110° relative from G. 



NOTE. — In case the speed of D is equal to the speed of G, the point X will lie in the given range circle. If the speed of D is less than the speed 

 of G, the point X will lie outside the circle, and the possibility exists of D .... X intersecting the range circle twice. In this event, the inter- 

 section nearer to D is the one to be used as Y. 



In the case the initial position of the Maneuvering Unit is such that the line D .... X does not intercept the range circle, then the problem 

 is incapable of solution. 





dw..-. 



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