There are MANY efforts of people setting out in an effort to cross the Sahara, that were successful. Many likely weren't. The Arabs did it, later the Europeans did, if you're telling me blacks never did you are likely wrong. Everywhere else in the world folks also built ocean going vessels and navigation abilities to follow the coast, except for sub-Sahara Africa.
I guess you blame it on mosquitos and army ants.
black africa DID have costal fishing vessels, canoes, and other watercraft long before the arrival of the colonial powers. they crossed the sea to madagascar (ZOMG!!!) but since that's the only land mass that can be reached without sails and long distance navigation from sub saharan africa, thats hardly an indictment.
black africa developed iron working independently, and only about 500 years after india (current winners for first known iron working), yet still a couple hundred years ahead of europe and asia minor.
what they didnt develop was advanced philosophies, complex social structures, writing, large scale agriculture, large scale animal husbandry, or extensive trade networks, but that too is not a trait exclusive to africa.
the new world didnt have iron working, domesticated animals (except the llama and some dogs) the wheel, the road, or in fact much of anything in the way of technology all the way into the 1500's does this imply that native americans are intellectually inferior, or is it simply that they DID NOT NEED ANY OF THAT SHIT?
the road is a product of The Wheel. if you have no wheels, you need no roads. you only need wheels if you are taking lots of something to someplace else, like say... a granary. if you do not need a granary, because you dont grow grain, you will never need a wheel.
you only grow grain if you will starve when the snows come because theres too many people to live off the land. if your population is small enough and mobile enough, you can just follow the herds of bison, and do quite well, or eat fish, or eat seal blubber, or, as in central and south america, you live in the tropics and all year is the growing season.
sub saharan africa is much like south america, a tropical land where you can grow whatever you want in a small patch any time of year or hunt at your leisure, thus you need no long term food storage solutions, thus no wheels, and thus, no roads, and thus no complex trade routes, and thus not complex societies, and thus no need for writing to keep track of shit, and thus no literature, etc etc etc etc.
unlike south america, africa is in close proximity to peoples who DO need long term food storage, thus did need wheels, bult roads, formed complex societies, assembled armies, and set out to conquer other people's shit.
this puts preassur on other nearby societies to compete, and the huge desert of the sahara (which was not there when the humans who became asians europeans and native americans left africa...) formed a natural barrier keeping the african populace blissfully unaware of their danger until it was too late.
likewise the native americans didnt see europeans coming, and by the time they figured out what was up, it was already too late for most of them.
TLDR Version: africa didnt develop technologies because they didnt need them, just like the aboriginal population in the americas. if negroes are naturally stupider that whitey, then native americans must also be stupider, but being even farther behind, they must be even DUMBER.
