THE TITANIC-50 YEARS LATER 



effectively hide dangerous growlers on the X-band. The reflective 

 quality of an iceberg is very low, about 60 times less than that of 

 a ship of equivalent physical cross sectional area. Due to the shape 

 and irregularity of the reflecting surfaces of icebergs, their range of 

 detection by radar varies greatly. An observant radar operator, ex- 

 perienced in ice detection, is a definite advantage. Often, even with 

 the expert use of the FTC and STC anti-clutter devices, dangerous 

 growlers can be lost in the sea return when a moderate sea is running. 

 If ice is not picked up beyond the area of sea return it will not be 

 spotted and the maximum range for the detection of a growler is 

 only about 4 miles. Usually, better results can be obtained from a 

 sector scan of a particular area, say 30° on each side of the bow, 

 than a general scan, and nearby ice which may not appear on the 

 minimum range setting often will appear on the intermediate or 

 maximum range settings. 



RADAR IS AN EXCELLENT AID FOR ICE DETECTION 

 WORK BUT EVEN WITH DILIGENT USE IT WILL NOT AS- 

 SURE A SAFE PASSAGE THROUGH THE ICEBERG AREA 

 OF THE NORTH ATLANTIC. 



RECENT EXPERIMENTS IN ICEBERG DESTRUCTION 



Although not primarily concerned with iceberg destruction, the 

 Ice Patrol, despite the previous unsuccessful attempts, evaluates 

 each new technique or theory that might hasten the disintegration 

 or melting of an iceberg. The highly successful aircraft offered a 

 practical approach to utilizing the thermite theory of ice destruction. 

 Therefore, aerial bombing experiments were conducted on selected 

 icebergs with thermite type bombs in June 1959. Each bomb con- 

 sisted of clusters of incendiary bomblets and was designed to open 

 about 100 feet above the target and spread the destructive power of 

 the thermite bomblets over a wider area. Sixteen out of the twenty 

 bombs dropped scored hits, but no icebergs were destroyed. The 

 heat, spread over too wide an area, did not deliver the concentrated 

 high temperature source necessary to the thermal stress theory of ice 

 demolition. The following year, 1960, high explosives were substi- 

 tuted for the thermite and twenty 1000-pound bombs were dropped 

 on a single iceberg for a total of 18 hits. The iceberg at the con- 

 clusion of the bombing was estimated to be one-fourth to one-third 

 smaller. Although natural deterioration was in progress throughout 

 the eight days of the experiments, the bombs were believed to be a 

 factor in the reduction of the size of the iceberg. 



The Ice Patrol felt that before further bombing experiments 

 were conducted the thermite theory should be re-evaluated. Due to 

 the great danger involved in boarding icebergs in the open sea this 

 had not been done previously, but permission was obtained from the 

 Canadian Authorities to conduct the experiments in the sheltered 

 waters of Bonavista Bay. Forty 28 -pound thermite charges and 

 related ice equipment were obtained for this experiment. A small 

 tabular berg was boarded and a 196-pound thermite charge planted. 

 The resulting explosion, aside from calfing a few small bergs around 

 the waterline, appeared to have little effect on the berg. Nearby, 

 a large pinnacle berg was boarded and a second charge of 560 pounds 



of thermite was planted at the base of the pinnacle. There was a 

 magnificient display of smoke and molten iron hurled hundreds of 

 feet into the air, but the iceberg remained virtually unchanged. 

 This experiment showed that this type of detonation will not neces- 

 sarily cause the disintegration attributed to the thermite theory. 



Iceberg 12 hrs after spreading carbonblack. 



Practice bombs filled with carbonblack, sand, ground clay, iron 

 fillings, and oil were also dropped from a patrol aircraft, but the 

 results were unsatisfactory. However, the small tabular berg used 

 in the first thermite experiment was reboarded on 10 June, in the 

 middle of the afternoon, and 25 pounds of carbonblack were spread 

 manually with fiber brooms over half of the iceberg. Five hours 

 later the berg underwent major calfing, and on close inspection the 

 following morning, it was found to be less than 1/3 its previous size. 

 The calfing of the iceberg after the carbonblack experiment could be 

 coincidental ; further experiment will determine the feasibility of 

 this type of deterioration. 



Spreading carbonblack on iceberg. 



WIND EFFECT 



For years the draft-height ratio for icebergs was believed to be 

 about 5 or 6 to 1, but recent wire drags and submarine observations 

 reveal a much smaller ratio. The approximate ratios for the various 

 types of icebergs are 7 to 1 for flat tabular bergs, 3.5 to 1 for spher- 

 ical shaped bergs, 2 or 3 to 1 for pinnacled bergs, and 2 to 1 for 

 drydock type bergs with the average ratio for all bergs somewhere 

 near 3.5 to 1. If the mean draft of icebergs is not as great as originally 

 estimated then the effects of surface winds on their drift should be 

 greater than previously believed. Therefore, in 1960, the Ice Patrol 

 conducted experiments to establish the proper relationship between 

 the wind and berg drift. Results obtained indicated that winds 

 between 10 and 50 knots imparted a drift velocity in knots of 

 0.023 that of the wind speed and in a direction 50° to the right of 

 the direction of the wind. 



42 



