Page 71 - Dutch Asiatic Shipping Volume 1

Close to the South American east coast for instance this wind is mostly a northeasterly. Where the northern and southern trade winds neutralize each other, in fact along the equator, there are usually calms. This zone is difficult to navigate and the influence of ocean currents is great.
In general the directions of ocean currents and winds coincide. Whereas for instance the southeast trade wind in the Indian Ocean near Madagascar veers to a southwesterly direction, the south equatorial current does the same. Map 5 gives a survey of the most important ocean currents. In the equatorial region of the Atlantic Ocean where there are as many as three directions, and again around Madagascar, shipping had to take this constantly into account.1
Map 5: Ocean currents
This pattern of winds and currents determined the main features of the seaway between Western Europe and Asia. The sailing capacities of the seventeenth and eighteenth century East Indiamen were of such a nature that tacking, i.e. criss-crossing against the wind, was extremely laborious and difficult. It was not possible to sail at less than six points of the compass (about 70 degrees) against the wind. The art of navigation did include the deter- mining of latitude in the open sea. The speed of the ship could be assessed fairly accurately so that with the aid of the compass and the knowledge of the variations of this instrument, the ship's course and its distance covered were usually determined on a daily basis. For correct position-finding however a method for determining longitude at sea was required,
1 A general survey of the routes in Sigmond, 'De Weg', Northcote Parkinson, Trade, 98-120, Tous- saint, History, 5-11 and Mauro, Le Portugal, 13-27. For contemporary interpretations of winds and currents see Burstijn, 'Theories'.