Though the Portuguese sailors had their maps and other navigational instruments with them, they encountered some problems and difficulties that they were not able to avoid. One was, they did not know what was the shape and how big Africa was. They did not know the routes yet and were unfamiliar with the trail.
Another is, though they did not have much trouble in sailing down the coast, getting back along the trail was a different story. They had a hard time sailing against the wind.