SURFACE-CURRENTS 155 



the Meteorological Office current charts and more or less on the main shipping lane from Capetown 

 to Sierra Leone. 



The current-system of the region affected by the south-east trade wind seems clearly explicable on 

 these lines, but although such an average picture may suffice for navigational purposes even in the 

 more variable inshore region, it cannot assist in the interpretation of the hydrological conditions 

 observed there. The irregularities already referred to show how much the inshore currents must 

 depend upon local wind and local conditions generally. For a significant interpretation of the water 

 movements here a synoptic rather than an 'average' picture would be needed. Existing data do not 

 suffice for this, but a practicable working compromise has been attempted by correlation of the 

 'William Scoresby's ' meteorological observations with the oceanographic data, and with the meteoro- 

 logical records of such other ships as were in the vicinity at the same time. 



Currents during the surveys 

 In March 1950, on the passage southwards from Lobito Bay, the first appreciable effect of current 

 was felt south of Bahia dos Tigres, where a moderate set to the north-east was noted. On the most 

 northerly line of stations (WS 964-70) an allowance of i° was made on the shoreward course for 

 northerly set, and this maintained a latitudinal line of stations, but it is impossible to say just how 

 much of this was the effect of current as distinct from the wind. At the stations on the outer end of the 

 Walvis Bay line, however, a northerly set of about 1 knot was encountered with a light wind ; the 

 observed position of station WS 978 lying 16 miles north-north-east of its intended position. This 

 northerly set was found at the offshore end of the three lines of full stations, and on the Walvis Bay 

 and Sylvia Hill lines gradually became more easterly as land was approached, until at the inshore 

 end of these lines the set was E.N.E. with negligible wind effect. 



At the inshore end of the most southerly line, just off the mouth of the Orange river, the set 

 appeared to be S.S.W., against a light wind from the same quadrant. 



On the second survey, in spite of the stronger winds, little genuine current effect was recorded. 

 Inshore at Orange river mouth, the ship, while lying-to for the night, showed negligible movement in 

 completely calm conditions. Seawards, however, between WS 1052 and 1053 there was a northwards 

 drift of 14 miles in 14 hr., but this may have been due to the wind. Between WS 1057 and 1061, the 

 first pure current-effect was noted, the ship being set 065 ° at \ knot with no wind, and at WS 1063 

 a slight north to north-east drift was probably due to the light south-west wind, and current must 

 have been almost absent. These conditions continued between WS 1064 and 1067 and on the circum- 

 navigation of Hollam's Bird Island there was no current at all. From 24 02' S., i3°5i'E. to 

 22° 46' S., 14 20' E. the current set 035 10 miles in \z\ hr., and later a similar set was observed off 

 Swakopmund where the vessel was stopped and drifted 035 for 3-5 miles in 5 hr. (0-7 knot). Again 

 when stopped off Pelican Point lighthouse at WS 1076 the set was 035 ° 07 knot with no wind. The 

 tide was on the flood then at Walvis Bay, and this may have accounted for the set. 



From WS 1081 to Walvis Bay no drift was experienced, and a perfect course was made. As the 

 winds were very light it is probable that there was negligible water-movement. After departing from 

 Walvis Bay no drift of any consequence was encountered, and currents were disregarded in setting 

 courses. 



Summing up, the set on both surveys appears to have been very little, but when it was observed 

 it was generally in a northerly direction in the offshore region, becoming more easterly nearer the 

 land. The S.S.W. set off the Orange river is inexplicable at the moment, and it is impossible to say 

 how much tidal streams were responsible for the E.N.E. sets experienced inshore. 



