APPENDIX E 



PHYSICAL PROPERTIES OF ICEBERGS 



Height to Draft Ratios of Icebergs 

 By R. Q. Robe 

 U.S. Coast Guard Research and Development Center 



A study of height to draft ratios of icebergs 

 near the Davis Strait reveals ratios which range 

 from 1 :1.28 to 1 :10.56. The ratios of bergs domi- 

 nated by their horizontal dimension average from 

 1 :4.26 to 1 :4.46. Bergs with a more vertical 

 nature, such as pinnacle or drydock bergs, have 

 ratios averaging from 1 :2.31 to 1 :2.41. The 

 smallest ratios are found in domed bergs, which 

 average 1 :6.30. The highest berg studied was 

 59 meters high, and the berg with the greatest 

 draft drew 161 meters. 



Introduction 



The draft of icebergs is of interest for a variety 

 of reasons. In areas where pipelines or cables 

 lie on the bottom, information on draft can be 

 used to estimate the probability of a break. For 

 the International Ice Patrol, the draft is of in- 

 terest because of the effect it may have on drift, 

 groundings and deterioration. Approximately 

 seven eighths of the mass of an iceberg is sub- 

 merged; however, this is not an indication that 

 the height to draft ratio is necessarily 1 :7. 



Estimates of height to draft ratios were made 

 as far back as the late 19th century. Steenstrup 

 (1893) gives the ratio as 1:7.4 and 1:8.2; while 

 Krummel (1907) gives a ratio between the ex- 

 tremes of 1:18 and 1:4, with most falling in the 

 range of 1 :5 and 1 :6. Grounded icebergs were 

 used to obtain the earliest estimates of the ratio. 

 Dawson (1907) found a berg stranded in the 

 Strait of Belle Isle in 1894 which had a ratio of 

 1 :3. Again in the Strait of Belle Isle, Rodman 

 (1890) found a 30-meter pinnacle berg grounded 

 in 29 meters of water for a ratio of nearly 1 :1. To 

 estimate draft, Smith (1925) used a drag wire 

 strung between two heavy weights and towed at 



known depths by two small boats. The small 

 boats, separated by about 137 meters, would pass 

 on opposite sides of the iceberg and lower the 

 weights till the wire passes freely under the ice- 

 berg. He found a ratio of 1 :2. During the 1959 

 ice patrol, Budinger (1960) examined the under- 

 side of an iceberg by diving under it. He found 

 that the berg had a height to depth ratio of 

 1 :3.3. Budinger also observed another berg 55 

 meters high grounded in 175 meters of water off 

 Cape Race (ratio of 1:3.2). Budinger erro- 

 neously states that the height to depth ratio can- 

 not be smaller than 1 :6. This was in conflict with 

 earlier estimates by Steenstrup (1890) and 

 Krummel (1907) and also was not substantiated 

 by data from the present study. Data collected 

 by the submarine USS SEA DRAGON, which 

 studied nine bergs, found height to draft ratios 

 which ranged from 1 :1.3 to 1 :4.2 (Murray, 1960). 

 The height to draft ratio was highly dependent 

 on the shape of the berg. The berg had to float 

 so that seven eighths of its mass was submerged 

 and so that the berg was stable. If, for instance, 

 the iceberg was tabular (flat top and bottom and 

 vertical side) a ratio of 1:7 would be expected. 

 If the above-water portion was rounded and 

 smooth, while the underwater part was pointed, 

 then a ratio smaller than 1 :7 could be expected, 

 even as small as 1 :9 or 1 :10. The other extreme 

 was the case where the underside of the berg was 

 rounded and smooth and the above-water portion 

 had towering vertical walls. The most pronounced 

 case of this type was the drydock berg where an 

 enibayment had been cut out of the center of the 

 berg leaving only a thin rim of great height and 

 little mass. These could have a height to draft 

 ratio which approached 1 :1. 



70 



