THE TITANIC— 50 YEARS LATER 



detection range may fall to 1 mile or less . In dense fog, an iceberg 

 may not be seen until it is close aboard and then it will appear as a 

 luminous, white mass if the sun is shining or as a dark, somber mass 

 if the sun is not shining. On a clear dark night an iceberg will seldom 

 be picked up at a distance greater than about ]4 mile, but if a sea is 

 running, the wave action against the base might be sighted as far- 

 away as 1 mile. A moon in the direction of an iceberg may hinder 

 its detection, while the light from a moon on the opposite horizon 

 may produce enough of a blink to allow the berg to be seen up to 3 

 miles. Often an icefield can be detected by a yellowish glare, or ice 

 blink, in the sky above the field; should there be snow on the ice the 

 glare will be whiter. If an iceberg is in the process of disintegration, 

 its presence might be detected by the cracking, roaring sound as calf ing 

 takes place. 



An early method of iceberg detection was the echo, and under 

 proper conditions it is still useful. Sound is reflected off at the same 

 angle it strikes a reflecting surface; thus, unless striking a steep- 

 sided or cliff-like face, the sound may reflect aimlessly off in a useless 

 direction. If the echo bounces back, the approximate distance and 

 bearing of the iceberg can be obtained. Abrupt changes in air and 

 sea temperature or the salinity of the sea water cannot be assumed 

 as a reliable sign of the approach to ice. Temperature and salinity 

 changes as great as those experienced in the Grand Banks area may 

 be experienced in many areas of the ocean that are entirely ice free. 

 However, it has been noted that icebergs tend to remain in the cooler, 

 less saline waters of the Labrador Current. 



Although the majority of the tremendous bulk of an iceberg is 

 submerged, early attempts to locate ice with a sonic fathometer were 

 unsuccessful. However, the fathometer was put to excellent use in 

 producing data for very accurate bottom contour charts of the area. 

 More recent Ice Patrol experiments proved that sonar can be useful 

 in detecting icebergs at relatively short ranges. Under favorable 

 conditions bergs may be detected at a range of about 3 miles and 

 growlers at about '2 mile. 



Before the advent of early radio aids to navigation, accurate 

 positioning was frequently impossible as atmospheric conditions often 

 prevented the patrol from obtaining celestial fixes despite many 

 ingenious methods perfected in early patrols. Radio compass and 

 radio direction finder equipment made this task easier. Improved 

 methods and equipment, such as the electric salinity indicator, 

 increased the scope of the oceanographic work that could be under- 

 taken. After establishing the position of an iceberg the prediction 

 of its drift remained a challenging problem. The patrol vessels 

 maintained up-to-date isotherm charts by plotting the sea surface 

 temperatures received regularly from vessels within the affected area. 

 These isotherm charts show the surface distribution of the warm 

 Gulf Stream and the cool Labrador Current and give an indication 

 of the general drift of the surface waters. However, a prolonged 

 wind or severe storm can mix the surface waters so that the under- 

 lying general drift of the water mass will be impossible to determine. 

 Since the bulk of an iceberg is underwater it is the deeper general 

 movement of the water mass that asserts the greatest effect on their 

 drift. 



Therefore, another method, involving the construction of a 

 dynamic current map depicting the unstable pressure conditions for 

 an entire water mass, offered a more reliable system of iceberg drift 

 prediction. This method required the undivided attention of a patrol 

 vessel for several days at a time, and was therefore impossible for 

 the Ice Patrol as constituted. The "International Conference on 

 Safety of Life at Sea," held in London during 1929, considerably 

 broadened the responsibilities of the Ice Patrol, in requiring "a service 

 for the study of ice and current conditions." Thus, from 1932 on, 

 a third vessel was employed each year for this scientific pursuit. 



The construction of a current chart depicting the dynamic 

 topography of the sea surface adjacent to the Grand Banks is a 

 scientific achievement of the oceanographer. To be useful, the area 

 to be charted must be of sufficient size to portray a fair picture of 

 the current circulation. Many oceanographic stations (50 to 100) 

 are taken as quickly as possible, usually in rows radiating out per- 

 pendicular to the slope of the Grand Banks. The oceanographer is 

 able to compute the relative dynamic or pressure height in decibars 

 of a water column at each station from a deep isobathic plane to the 

 sea surface. In oceanographic work, water pressure or dynamic po- 

 tential is commonly expressed in decibar units. This unit is con- 

 venient because it is very close to the pressure exerted by 1 meter of 



water. Thus the pressure height in decibars of a water column is 

 approximately the same as the depth of the column in meters. 



Because sea water is not a homogenous substance, particularly 

 in the critical iceberg area near the confluence of the warm, salty 

 Gulf Stream and the cool, less saline Labrador Current, the computed 

 relative pressure heights in decibars will vary from station to station. 

 The oceanographer plots each station geographically with its cor- 

 responding pressure height, then by scribing a line through areas of 

 equal pressure heights he obtains a chart depicting the dynamic to- 

 pography of the sea surface. The resulting chart closely resembles an 

 isobar weather map and actually portrays Highs and Lows in the 

 pressure level of the sea surface. Thus, in the Northern Hemisphere, 

 the unequal water mass from the Highs, attempting to equalize the 

 depressions, flows counter-clockwise around the Lows similar to the 

 flow of an air mass around a barometric low. However, if the com- 

 plicated details of the water circulation are to be determined, oceano- 

 graphic stations must be placed much closer together than weather 

 observation posts, with the density of stations even greater along 

 the slope of the Grand Banks than in the deeper water off the Grand 

 Banks. Whereas, a weather map may be constructed in hours, and 

 is useful only for hours, the construction of a current map takes days 

 but it is useful far longer, as the rate of the everchanging water 

 circulation is slower than that of an air mass. 



EARLY EXPERIMENTS IN ICEBERG DESTRUCTION 



The shapes, sizes, heights above water, and depths below water 

 of icebergs differ tremendously, each variation contributing to the 

 many variable factors determining their drift. Observations have 

 shown that, with the best current charts available, drift predictions 

 are not always accurate. Consequently, if the rather short life span 

 of an iceberg in the critical area south of the Tail of the Banks could 

 be shortened by only a few days it would greatly, percentage wise, 

 reduce the time it is a menace to navigation. Experiments in arti- 

 fically increasing the meltability or in the demolition of icebergs 

 have been carried out intermittently by the Ice Patrol since its 

 beginning. These experiments have included sound, gunfire, mines, 

 demolition charges, depth charges, and even fire hoses. All attempts 

 have had no real practical results. However, studies available 

 revealed that with the strategic positioning of half a ton of conven- 

 tional explosives about 2,000 tons of ice can be broken up, but this 

 could require upwards of a hundred charges to destroy a berg and 

 would be both physically and economically unsound. Melting by 

 heat would be equally impracticable as it would require the heat 

 energy contained in 2.4 million gallons of gasoline to melt a medium- 

 sized berg of 100,000 tons. 



Plane and iceberg target after bombing 



The Ice Patrol has long been aware of the experiments, results, 

 and theories of the late Professor H. T. Barnes, of McGill University, 



40 



