How does first witch curse the sailor? Why do you think she just doesn’t destroy his boat?

The first witch casts a storm on the sailor and make him suffer, Sleep shall neither night nor day Hang upon his penthouse lid. He shall live a man forbid. Weary seven nights nine times nine Shall he dwindle, peak, and pine.

Witches could affect the weather but they could not outright kill the sailor. "Though his bark cannot be lost, / Yet it shall be tempest-tossed,”