Indentured servants worked for the owner of their contract, which had a term limit. Once the term was up, the worker could continue with their life. An enslaved person was treated like property to be bought, sold, traded, or destroyed at the will of the owner. Complicating this issue is that there were multiple cases of early indentured servants who were black with finite contracts.
Fully twenty-five percent of mariners and other members of seagoing trades were African Americans--some free, some enslaved. Their skill sets ranged from new hands taken on board for a voyage all the way to captain and owner of a seagoing vessel. There were many pilots—free and enslaved—working the sounds of the Carolinas, and the fluctuating local laws about where they could and could not sail, drove transiting captains to desparation.
Look up John Carruthers Stanly, trained as a barber in New Bern, North Carolina. Or query Marie Therese Metoyer of Louisiana, who was trained in nursing and pharmacology and died a wealthy woman. Then, maybe Google William Ellison of South Carolina, who sided with the South, bought bonds and committed some of his slaves to the Confederacy as soldiers. He lost his wealth, but still held slaves when he passed.
A History of World Societies documents 6,000 Black enslavers in the U.S. in 1840. Subsequent documentation of the owner's race became ambiguous, for the most part, but the reality had been established and recorded in that last complete census. In TheTide Waits for No Woman, Ben Hill was a fugitive whose non-fictional master was one of these 6000. Before immigrating to Liberia, Ben’s master broke the law by teaching Ben to be literate in both language and arithmetic. The details of that are in the novel and are taken from a contemporary first-person account