Was there a Silk Road at sea, and who really sailed it?

Yes, there was, and for a long time the people sailing it were not Chinese. The Maritime Silk Road was an ancient maritime trade route across the Indian Ocean and Western Pacific. It began by the 2nd century BCE and flourished until the 15th century CE. It is described as primarily established and operated by Austronesian sailors in Southeast Asia, who sailed large ocean-going ships built with sewn planks and lashed lugs. Persian and Arab dhows and Tamil merchants used it too. China started building its own trade ships only later, from the 10th to the 15th centuries.

The name is modern, copied from the overland Silk Road. For most of its history the route had no name at all, and it carried a wide variety of goods, not just silk. Unlike a caravan route, it let traders travel the whole distance instead of relaying goods from town to town, and ships could carry far larger amounts of goods than caravans.

It also carried people and beliefs. Han and Tang records show that early Chinese Buddhist pilgrims heading for South Asia booked passage on the Austronesian ships that traded at Guangzhou. Sanskrit became the trade lingua franca of the early route by the 4th century CE.

So when we picture silk moving between East and West, part of the story is also a story of sails: a sea route as old as the land one, run by other hands.