Interesting question! In the book The Slave Dancer by Paula Fox, Jessie witnesses his first whipping on the ship.

In the story, Purvis is declared to be the thief of the Captain’s personal food. The Captain keeps a personal supply of food for himself, including eggs. During this chapter, one of the eggs is stolen. Although Purvis is innocent, he receives the blame and punishment for the action.

Consequently, Purvis is tied and flogged. After the flogging, Purvis is further punished by being tied to the shrouds of the ship. As the Captain declares:

“'Now tie him to the shrouds,’ said the Captain. ‘The air will refresh his corrupt soul.’”

Although these actions do not shock the crew, Jessie is quite surprised and horrified by these events. As a result, he struggles with sleeping after witnessing the events. As Jessie reveals:

“I barely slept that night. Once, I peeped out at the deck. Far above, like a huge tattered bird, its wings flapping, hung Purvis, tied to the shrouds where the wind beat against him as though animated by the same demon which had raised Nicholas Spark’s arm and brought the tarred rope down on his back.”

Thus, the chapter is named after the shrouds due to the horrible punishment inflicted on Purvis during the chapter. Although it does not shock the crew, it makes a profound impact on Jessie.