In the 1300s Mansa Musa wrote of his predecessor;
“He ordered the chief (admiral) not to return until they had reached the extremity of the ocean, or if they had exhausted the provisions and the water. They set out. Their absence extended over a long period, and, at last, only one boat returned.”
“On our questioning, the captain said: ‘Prince, we have navigated for a long time, until we saw in the midst of the ocean as if a big river was flowing violently. My boat was the last one; others were ahead of me. As soon as any of them reached this place, it drowned in the whirlpool and never came out. I sailed backwards to escape this current.’
But the Sultan would not believe him.”
The story given by the captain was not believed. The idea of a whirlpool or the ‘end’ of the Earth and edge one could drop off, was not believed by Africans in the 1300s.