On 26 October 1771, Smeathman embarked at Gravesend on a ship aptly named the Fly. Patrick Lothian was in command, on what appears to be the first of several slaving voyages he captained from London to Senegambia and Sierra Leone. When Smeathman got on board the legacy of the ship's recent visit to the tropics was visible in certain stowaways, namely numerous cockroaches and ants. The historical record tells us that there was to be another, much more gruesome legacy on the return leg of this triangular voyage.1 After depositing Smeathman at the Isles de Los, the Fly picked up 250 slaves but delivered only 208 into the maw of the fast-growing West Indian island of Grenada. This was a mortality rate of almost 17 per cent, considerably higher than the 12.5 per cent which William Wilberforce argued in 1789 constituted the average loss of life on the middle passage.

It was a very rough passage to West Africa, in which Smeathman and his draughtsman David Hill suffered badly from seasickness. There were violent winds, ‘coruscations of forked lightning’, and a raging ocean, all of which meant ‘various insurrections of Chairs, Tables, chests, & crockery ware’ in his cabin. That this was not Smeathman's first sea voyage is clear from his decision not to repeat the stunt that he had once performed on a particularly bad crossing from Calais to Dover. Suffering from seasickness, he had resorted to quaffing a quart of cold sea water ‘in a kind of bravado’, a stunt which had left him severely ill. Since Fothergill had no specific location in mind beyond ‘the coast of Africa’, and Drury had been in correspondence with the slave traders on Bunce Island, the Sierra Leone area probably seemed as good a place as any for Smeathman to disembark. A peninsula on the upper Guinea coast, the region was named Sierra Leone by the Portuguese, meaning ‘the mountain of lions’.