There is always more to say, but some earlier responses here address some aspects of your question, and you might like to review those threads while you wait for fresh responses to your query.

This thread led u/Commustar and this thread, led by u/MansaMontezuma, address the question of whether the fleets actually existed.

Meanwhile, this other thread, with u/amp1212, takes a look at the technological and navigational capabilities of contemporary African sailors and shipbuilders, and finds reason to doubt they were capable of building and sailing transatlantic craft.