The sailing route from the China tea ports to London is across the China Sea, then the Indian Ocean, passing Mauritius, rounding the southern tip of Africa into the Atlantic, generally passing to the west of the Azores before turning towards the English Chanel. The major variations were in the China Sea, with different strategies to pick up favourable winds. A direct route to the Indian Ocean is through the Sunda Strait. Circumstances (such as a strong south-westerly wind immediately on departure) or a cautious captain may dictate use of the "Eastern Passage". This meant heading out into the Pacific Ocean, going down the eastern coast of Formosa (Taiwan) and the Philippines, then through the Gillolo Strait, Pitt Passage, and the Ombai Strait into the Indian Ocean. This longer route did not necessarily result in a slow passage: Sir Lancelot took 99 days from Woosung (Wusong) to London by this route in 1867.
Ariel's homeward passage the Great Tea Race of 1866.
The distance from Foochow to London is described as being "over 14,000 miles" by MacGregor. Ariel logged about 15,800 nautical miles from China to London on her 1866 passage.
The start of the tea season was during the early stages of the South-West monsoon in the China Sea, so head winds would be experienced, and very light or variable winds together with sudden squalls. Many captains sailing for the Sunda Strait therefore chose to head westward to the coast of Annam (present day Vietnam) to pick up land breezes. This involved tacking at the most favourable moment to be close inshore for the start of the land breeze, often in the middle of the night.
Crossing to the Annam coast meant passing the Paracels, an area of low-lying islands and reefs which presented obvious dangers. From the coast of Annam, the usual route was to head south to the coast of Borneo, again to take advantage of land and sea breezes.
The crossing of the China Sea frequently decided the overall passage time to London. It also had notable hazards, particularly as accurate, fully surveyed charts did not exist at this time.
The five ships leading the 1866 race all headed for the Sunda Strait, sailing past the Paracels, down the coast of Annam and then south to Borneo, bound for Anjer, on the southern side of the Sunda Strait.