97 



very much at variance with the ordinary conception of the flow of 

 the Gulf Stream drift but in direct agreement with the direction of 

 drift which would. have been predicted from an inspection of the local 

 surface isotherms on the chart. 



But watching the drift of bergs and other passively floating bodies 

 is not the only available means of ascertaining local currents. The 

 moderate wind conditions that usually prevail in the ice-patrol area 

 during the last half of the patrol season enable that portion of the 

 patrol ship's own drift which is due to current alone to be rather 

 accurately determined during times of good visibility. 



The value of current determinations of this sort varies with the 

 accuracy with which the vessel's observations of the heavenly bodies 

 are made. Methods of position fixing by means of soundings and 

 radio bearings, though at all times useful for check purposes, and 

 necessariljT^ relied upon during foggy and overcast w^eather, are not 

 exact enough to be of much use for accurately determining ocean 

 currents oft" the Tail of the Grand Banks. On the other hand, the 

 positions obtainable through celo-navigational methods during 

 favorable periods are at times dependable within a radius of not over 

 3 miles, and so quite valuable for this purpose. 



Position fixing is of prime importance to the ice patrol for a num- 

 ber of reasons and great attention is paid to it. The most modern 

 methods of handling the observational and chart work are followed. 

 Positions are checked by independent work of at least two experienced 

 navigators. 



Spending most of its time searching relatively small areas near the 

 temperature wall between the Gulf Stream and the Labrador Current, 

 drifting at night, and keeping track of its position as it does, it is 

 believed that the ice patrol is at man}^ times particularly capable of 

 observing the rates and directions of the local currents. Many of 

 these currents are so restricted in size and vary so much in direction 

 over the course of one or two hundred miles that they are frequently 

 averaged out and lost during the long runs made daily by ships bound 

 east and west across the ocean at speeds exceeding 8 or 10 knots. 



In three cases when the ship's location was well determined strong 

 currents were observed during the 1929 ice-patrol season, as follows: 

 On April 25 and 26, a sustained 2.6-knot current setting east and 

 northeast along the forty-second parallel between 49° W. and 51° W. 

 On June 7, a current setting southeast over 2 knots near 41° 38' N., 

 48° 56' W. On June 24 and 25, a 2-knot easterly current near 42° 

 N., 50° W. In every case the existence of these strong currents is 

 fully indicated by the position of the curves on the isotherm charts. 

 When a well-developed cold wall exists between the Gulf vStream and 

 Labrador Current a rapid flow parallel to the isotherms seems to be 

 characteristic. 



