On first reading, this event that occurs at the very end of the chapter seems a rather strange act. Cromwell chooses to drop the one item that connects him to his older sister, Kat. Note how this event is described:
Kat has given him a holy medal to wear. He has slung it around his neck with a cord. It makes a chill against the skin of his throat. He unloops it. He touches it with his lips, for luck. He drops it; it whispers into the water.
However, when the reader remembers what Cromwell is fleeing from, which is the brutality of his father who physically abused his son, the relinquishing of this holy medal could be seen as an act of independence. Cromwell is leaving England determining to make his own way in the world without anybody else's help. The medal he receives from Kat appears to be uncomfortable in the "chill" it makes against his throat. The medal could be seen as the last thing that binds him to England and his last link with his family. Dropping it into the sea is therefore a powerful statement of independence and also a symbolic ending of his childhood as he makes his own fortune abroad. When Cromwell returns to England, he will be a very different man indeed.