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edge of by far the largest part of the great area lying between the 

 United States and the Canadian tracks. This area is large when the 

 patrol season starts, but it becomes very much larger as the advance 

 of the spring melts back the field ice and permits the Canadian tracks 

 to be shifted farther and farther north. It goes without saying that 

 the value to the patrol of temperature and ice reports from vessels 

 crossing between the usual tracks is inestimable. A large gain would 

 be effected by the ice-patrol service if all such vessels would report 

 their positions and water temperatures regularly instead of remaining 

 silent unless they see ice, as it appears a number of them still do. 



Those passenger vessels which cut to the north of the tracks that 

 are in effect (and the patrol noted, in 1929, 100 different cases where 

 vessels carrying passengers were 20 miles or more north of their pre- 

 scribed lanes), if they do not take rigid extra precautions, decrease 

 their chances of coming through the ice regions safely. Their masters 

 should bear in mind the fact that the ice-patrol broadcasts do not 

 necessarily list all the icebergs in any area, but only the icebergs of 

 which the patrol and the reporting vessels have knowledge. The 

 positions of ice in the broadcasts are always subject to a certain amount 

 of observational en or in the first place, and they become less and less 

 reliable as time goes on, due to the impossibility of accurately fore- 

 €asting berg drifts. Hope to make absolute determinations of future 

 berg drifts can be expected neither from construction of dynamic cur- 

 rent maps nor isotherm and ice charts. The best that can ever be 

 hoped for is some reasonable approximation of the most probable 

 courses and rates of movement that given bergs will take. 



South of the Tail of the Banks reported positions of bergs, even if 

 correct within a mile to begin with, are normally subject to a 24- 

 sea-mile radius of error with every day that passes from the time of 

 the last report of them. Occasionally swift currents cause the radius 

 of error to reach 48 sea miles daily, and very exceptionally to approach 

 72 sea miles per day. The dates given with the positions of the south- 

 ernmost bergs enable the recipients of the broadcasts to determine 

 within 24 hours the time the different bergs were last reported or 

 sighted. This permits their making a very rough approximation of 

 probable berg locations when knowledge of the usual drifts of ice is 

 at hand. 



Some passenger liners, both eastbound and westbound, maintain 

 notoriously high rates of speed, such as 20 knots, more or less, ac- 

 cording to ability, even during periods of fog and darkness. The 

 ice patrol has noted that a few of them actually maintain such speeds 

 during bad visibility conditions when they are 100 miles and more 

 north of their proper tracks. Such action is extremely foolhardy and 

 is bound to result sooner or later in disaster. 

 100277—30 7 



