METHOD OF SAFE NAVIGATION IN FOG. 123 



Any attempt to obtain a definite bearing would require the vessels to change 

 course and head for each other, a maneuver decidedly objectionable and danger- 

 ous. In fact most collisions at present occur after the steam whistles are heard 

 while maneuvering to avoid each other. 



Even if we assume that handling two vessels in a fog by heading for each 

 other is permissible, the accuracy of the result would depend, first, upon the re- 

 ceivers having the same sensitiveness, and, second, the judgment of the observer in 

 comparing them. In practice microphones are rarely found alike, and the same set 

 varies from day to day. It has also been suggested that the loudness of the sound 

 could be used as a measure of the distance between the vessels. Experience in sub- 

 marine signaling demonstrates that the intensity of the sound received depends 

 not only upon the distance but also upon the angle it strikes the outer plate of the 

 receiving tank, the speed of the vessel, the state of the sea, the condition of the 

 microphones, the rolling and pitching of the vessel, and probably also upon the state 

 of the water itself. A practical mariner would hardly trust the safety of his ship 

 to an equation with so many variables. The submarine signal furnishes a neces- 

 sary element in the problem of fog navigation, but is not in itself sufficient to secure 

 safety. 



For many years since the advent of wireless, efforts have been directed to its 

 use as the solution of fog navigation. On shore the installation of the umbrella 

 type of directional aerials has been attempted where signals are transmitted over 

 each wire in turn arranged radially. The relative strength of the signal is used 

 to determine the direction. A modification for shipboard of "two directive aerials at 

 right angles to each other and an instrument called a radio goniometer have been 

 used to determine the bearing of the sending station. This radio "angle measurer" 

 is rotated to the point where the received signal is most intense, thus indicating the 

 bearing of the sending station or vessel. 



Vessels equipped with directive aerials and the radio goniometer could there- 

 fore communicate to each other in a fog their courses and speeds, and, so far as the 

 accuracy of the instrument permits, gain an idea of their relative bearings. 



The deficiencies of this method alone for securing safety in fogs are not unlike 

 those of the submarine wireless. No definite information of the distance between 

 vessels is obtained as the intensity of the signal depends upon numerous variable 

 conditions, and the accuracy of the bearing depends upon the judgment of the ob- 

 server as to the relative intensity of the signals. While possibly capable of accuracy 

 when tested by a skilled observer in a laboratory, the fact that the intensity is not 

 sharply defined but follows the sinusoidal curve would cause the practical naviga- 

 tor to mistrust its use as a sole dependable means of safety. Neither the submarine 

 wireless alone nor the directive aerial wireless alone is sufficient. In case a choice 

 were to be made between the two, the directed wireless would probably be pre- 

 ferred, on account of its more reliable range and the ability to determine the ap- 

 proximate bearing without altering the course of the vessel. 



The U. S. Naval Institute in its last quarterly publication contains an interest- 



