Jed, if you're particularly interested in runaway slaves serving on board ships, you might find the following two books useful:

W. Jeffrey Bolster, BLACK JACKS: AFRICAN AMERICAN SEAMEN IN THE AGE OF SAIL (Harvard U. Press)

Graham Russell Hodges & Alan Edward Brown, eds., PRETENDS TO BE FREE: RUNAWAY SLAVE ADVERTISEMENTS FROM COLONIAL AND REVOLUTIONARY NEW YORK AND NEW JERSEY (Garland Publishing)

It was a common worry among slaveholders that captives would join a ship's crew; many African Americans were skilled in various seafaring trades (not just sailing but sailmaking, ropemaking, shipbuilding, coopering, cooking, language translating, etc.), and many captains were anxious enough to put together a crew that they didn't ask too many questions.

I have been directing a project to reinterpret a museum site in New York's Hudson Valley, Philipsburg Manor, and in the process have found some interesting references to runaways from the Philipse family who sailed off as far away as Madagascar in the late 17th century. PM me if you want to know more.

Margaret