"Bloody Jack" by L.A. Meyer (Preowned Paperback)

While disguised as a boy, Jacky Faber experiences adventure and romance on the high seas.

Life as a ship's boy aboard HMS Dolphin is a dream come true for Jacky Faber. Gone are the days of scavenging for food and fighting for survival on the streets of eighteenth-century London. Instead, Jacky is becoming a skilled and respected sailor as the crew pursues pirates on the high seas.
There's only one problem: Jacky is a girl. And she will have to use every bit of her spirit, wit, and courage to keep the crew from discovering her secret. This could be the adventure of her life--if only she doesn't get caught. . . .