METHOD OF SAFE NAVIGATION IN FOG. 125 



This very considerable interval renders it easy to measure the distance be- 

 tween vessels with greater accuracy than necessary for purposes of navigation. 



After arriving within range of the submarine wireless signal, the vessels are 

 able to know at all times their distance within an error that should not exceed 300 

 yards. 



Figure 10, Plate 49, shows diagrammatically the apparatus used for sending. 



A shaft (75) is rotated by a clock or uniform speed motor one revolution per 

 second. This carries a wheel (74), which is shifted along the shaft according to 

 the speed from 6 knots to 30 knots, and this wheel meshes into the spur gear shown 

 having the number of teeth corresponding to the speed in knots. A complete revolu- 

 tion of one of the spur wheels releases the cam cylinder (51), on the surface of 

 which are cut the Morse characters corresponding to the courses. When this cyl- 

 inder revolves the cams pass under the two keys of the wireless and submarine wire- 

 less adjusted to cause simultaneous signals to be sent. These keys are adjusted 

 for the course of the vessel. 



A vessel, course north, at 10 knots therefore automatically signals the letter 

 "A" every 10 seconds. A vessel running into a fog would have only to throw the 

 switch to signal her course and speed, and any vessel hearing the above letter would 

 know her course and after one or more repetitions would be informed of her speed. 

 As soon as the submarine signal is heard the successive distances separating the 

 vessels are constantly obtained. 



The instrument for graphically measuring this distance is shown in Fig. 11, 

 Plate 50. 



The horizontal shaft is the same as shown in Fig. 10, rotating uniformly one 

 revolution per second. The observer hearing both signals has only to press the 

 Morse key (130) on receipt of the wireless and release the key on receipt of the sub- 

 marine signal. By operating a solenoid the horizontal lines are generated as shown 

 on the traveling sheet which is graduated in miles and tenths, or 200 yards. It is 

 thus easy to keep constantly informed of the speed, course and distance of any 

 vessel within the radius of the submarine signal. It might appear that this in- 

 formation is all that is necessary in navigating through fogs, but a great deal more 

 is required by the practical seaman who naturally preserves his speed and course 

 wherever possible, and who wishes to know whether or not his bearing is changing. 

 Fortunately, a method is now available for giving him this vitally needed informa- 

 tion in ample time to avoid collision, and where he is able in most cases to proceed 

 without change of speed or course, with positive information in no wise dependent 

 on the judgment of the lookout as to maximum sound direction. 



In Fig. 12, Plate 51, is shown a simple instrument consisting of four jointed 

 straight edges graduated in knots and tenths. To explain its use it should be re- 

 membered that when two ships are under way with uniform course and speed, at 

 any particular time there is only one bearing combined with one distance which 

 would cause collision. 



