126 SUBMARINE SIGNALING AND A PROPOSED 



Referring to Fig. 12, assume that both vessels are at the center 140. This con- 

 struction was adopted to simplify an otherwise awkward construction. Assume the 

 course and speed of the first vessel to be (145), and that of the second vessel to 

 be (146). If collision were to occur the second vessel would then actually be at 

 (144). The rate at which the vessels would approach to collide would be 140-144, 

 which is conveniently ascertained by swinging one of the graduated arms 175 or 

 176 over to read the collision rate of approach in knots and tenths. 



Referring now to Fig. 11, this collision line is ascertained as soon as the wire- 

 less letter of another vessel is heard, and the parallel ruler (155) hinged at the lower 

 end is swung over and clamped to the corresponding speed shown on scale (153)- 



As soon as the first submarine signal is received this parallel ruler is used to 

 strike the collision line on the diagram, and the observer thereafter has only to note 

 whether or not the actual distances measured follow or fall outside this line. 



In case collision is to occur the bearing of the vessels does not change exactly 

 as in the test prescribed by the "Rules of the Road," the rate of approach is uni- 

 form, and the successive distances measured would generate a straight line. If the 

 bearing changes the successive distances generate a curved line. 



It is now clear that by applying the "collision line" (106) in Fig. 11 to the dis- 

 tance first obtained it will show very soon whether or not the actual approach fol- 

 lows the collision line — in other words, whether the two vessels are changing their 

 bearing. 



A diagram will best illustrate this. Fig. 13, Plate 51, is a simple example of 

 two vessels at A and B, each having an assumed speed of 15 knots on courses 90 

 degrees apart, each 5 miles from the point of crossing C By preserving the speed 

 and course collision would occur in the time necessary to run 5 miles, namely, 20 

 minutes. 



In this case the solid lines show their successive positions, the bearings do not 

 change, the triangles are similar, and the rate of approach is uniform. 



If the speed of "B" is assumed as 21 knots she hauls ahead of "A," the bear- 

 ings change as shown in the small dotted lines, and the rate of approach is non- 

 uniform. 



The same result occurs if "B" has a speed of 9 knots as shown in the broken 

 lines, except that in this case "A" hauls ahead. 



Referring now to Fig. 11, in the above cases the results would appear as shown 

 in Fig. 14, Plate 51. The solid line B would be generated if collision occurred as 

 in the first case. 



In the second case the collision line would appear as Bi and in the third case as- 

 sumed as B2. The dotted curves show the actual distances. If collision were to be 

 possible the vessel would have to be at the points in Fig. 13 marked Bi and B2 

 respectively. 



Other illustrative examples of the records in the receiver are shown in Figs. 

 A and B, Plates 52 and 53, supplementing Figs. 13 and 14, Plate 51. In the latter 

 cases vessels at B were assumed to have various speeds but keeping the same 

 course (180°). In Figs. A and B vessels at B are assumed to be steering various 



