Speaking quickly about the legendary expedition of Abu Bakr. One have to really understand the source it was mentioned : an account of Musa I's hajj by an Arab chronicler.
The parallel is quite clear : one is a pious muslim, abide by the hajj and goes east leaving a reputation of wealth, generousity, knowledge and grandeur. The other goes west on the great sea, is only known to be dead for a far objective.
While you may have a genuine expedition, this heavily symbolical text is the only account we have for this mansa and a fortiori the expedition : simply said there's no material traces of such strong marine in western Africa.
Back to the main question.
The vital artera of western african cultures in middle ages were the terrestrial roads : it was simply more convenient and you really have to wait the European tentatives to bypass Islamic trade of Africa in the XVth to see a real change. There's simply no real motivation to do otherwise.
As for Eastern shores, that's different : since Pharaonic times, you did have a maritime trade with the Horn of Africa, and further south and other centers in Near East and Indias (think Somali or Swahili city-states).
But, it was essentially at the initiative of these cores, not eastern African entities that had more a role of middle-men with hinterland peoples (once again favouring land ways).
But, if you'd want a more active African maritime power, you'd have to search rather in Eastern Africa, as you at least had a long and important history of maritime trade (one could argue that the Sultanate of Oman was as much an African maritime power than Arab, and there's room for this argument)
The main obstacles are the harsh hinterland especially for irrigation, and more generally for the important production of trade goods : the problem was partially overcome in the XVIth century with Ajuran, but too late.
I'd think an earlier Persian presence on the Horn, as it existed in Eastern and Southern Arabia, in Antiquity, could provide enough of a boost to see hegemonic mercantile power. Of course, saying that butterflies would be huge would be an understatement.
If you're looking for sources, the freely avaible UNESCO History of Africa should interest you.