near the Grand Banks region. The bergs were 

 surrounded by an array of floats (styrofoam 

 cylinders) connected by buoyant line 

 (polypropylene, %" diameter). The length of this 

 line varied from 400m to 800m depending upon the 

 size of the iceberg. A spar-type, buoyant RDF 

 transmitter (Finders Buoy, Ocean Applied 

 Research Corporation) was included in the line 

 circle. One hundred and eighty degrees from the 

 transmitter was a spar buoy with either a radar 

 reflector for electronic detection and /or red flags 

 for visual detection (Fig. 9). 



Each RDF transmitter had a different transmis- 

 sion frequency to permit positive identification 

 independent of visual observation. The buoys were 

 located with an automatic direction finder (Ocean 

 Applied Research Corporation manufacturer) 

 mounted on the bridge of the CGC EVERGREEN. 

 The antenna for this system was secured to the 

 railing just forward of the bridge. Early attempts 

 at locating the RDF transmitters using handheld 

 receiving sets were frustrated by the apparent om- 

 nidirectionality of the signal at ranges closer than 

 3700m as well as directional ambiguity at greater 

 distances. 



The tagging arrays were deployed from the CGC 

 EVERGREEN during April and June of 1974. 

 This was accomplished by casting off a spherical 

 float attached to one end of the line. The ship 

 circled the iceberg playing out the line until the 

 float could be recovered. The two ends of the line, 

 each having eye splices and thimbles, were joined 

 together with a shackle. The tethering ring of the 

 RDF spar buoy was attached to the shackle and 

 placed in the water. The iceberg, thus encircled, 

 carried along its array as it drifted. 



During the first cruise (April /May 1974) the 

 iceberg tagging project was plagued with the 

 difficulty of locating suitable icebergs for tagging 

 (i.e., small enough to tag) in the survey area. After 

 three had been successfully deployed, all were 

 carried from the icebergs during a storm which 

 lasted two days. Winds reached 19.5 m/sec, and 

 seas increased to 5 meters. Only one of these 

 arrays was eventually recovered. The line on the 

 recovered array was broken in two places. One 

 break appeared to be the result of chafing. The 

 other break occurred with such force that the ends 

 of the polypropylene strands were fused together. 

 In this case there was no sign of chafing. Because 

 of these problems, little useful data were obtained 

 on this cruise. 



More favorable weather for iceberg tagging 

 prevailed during the second cruise (June /July 

 1974). Therefore, the CGC EVERGREEN, using 

 similar arrays was able to track several icebergs in 

 dense fog for nine days. 



ICEBERG DRIFT RESULTS 



The drift of the six icebergs was determined for 

 the time between observations as often as possible 

 during the period 20/0911Q to 29/0138Q June 

 1974. Individual icebergs were tracked from 1.6 to 

 4.8 days. Wind velocities were logged hourly by the 

 CGC EVERGREEN'S bridge watch. All icebergs 

 tracked during the experiment were located in the 

 area bounded by 44°30'N to 47°30'N and 47°00'W 

 to 48°30'W. Air temperatures during the iceberg 

 tagging project ranged from 3.9°C to 9.4°C with 

 an average about 6.4°C. The surface sea water 

 temperature for the same period ranged from 

 1.1°C to 10.6°C with an average about 3.9°C. The 

 weather was predominantly overcast with fog and 

 visibility typically less than 100 yards for the entire 

 drift survey. The sea state was moderate to calm. 

 The data from observations taken during the 

 second Ice Patrol cruise of 1974 are summarized in 

 figure 10. 



The vector-averaged drift for the icebergs varied 

 from 0.2 knts for iceberg No. 1 to 1.1 knts for 

 iceberg No. 6. The average drift speed to average 

 wind speed ratios ranged from .016 to .085. An 

 expendable surface current probe (EOTECH 

 Corporation) was deployed in the van of iceberg 

 No. 6 and measured a surface current of 1.23 knts, 

 setting at 193°T. This compared to the iceberg 

 drift of 1.1 kns at 212°T. The wind was 13.5 knts 

 from 319°T. 



The drift angle for the individual icebergs with 

 respect to the wind direction had a large range of 

 standard deviations from ±18° to ±81°. 

 Furthermore, a number of observations (14%) 

 indicated drift angles to the left of the wind. Ettle 

 (1974) had iceberg drift data from past Ice Patrol 

 cruises that gave a range of standard deviations 

 for drift angles from ±54° to ±104°. 



The frequency distributions of the individual 

 drift angles and drift speed: wind speed ratios (Fig. 

 11 and Fig. 12) for the 1974 drift data, reveal the 

 fact that the majority of the drift angles occur to 

 the right of the wind direction as expected in the 

 Northern Hemisphere; however, the distribution of 

 drift angles is continuous from 20° to 130°. The 

 range extends from -116° to +180°, virtually all 

 quadrants of the compass. The one iceberg (No. 1) 



