Epstein mentioned the practice of contracting out slaves to fill out crews on ships.

Yankee ship owners were abolitionists only in part- William Lloyd Garrison (1805-1879) spoke out against and printed attacks on the New England merchants who continued in the slave trade all during the first half of the 19th c. Maryland courts convicted and jailed Garrison for his attacks on one such trader; he had to leave Baltimore.

See Hugh Thomas, 1997, "The Slave Trade," Simon & Shuster.