Heart of a Samurai by Margi Preus

As the days went on, Manjiro learned how to shorten sail, sheet home, trice up, and trim and make sail. He learned how to scrub the deck with soft sandstone tools known as "holy stones. " The main deck was scrubbed with a "bible" and the hard-to-reach corners with a "prayer book."

"They aren't really those things," Itch said. "A bible is a holy book, see, and a prayer book is, too. You wouldn't really scrub a deck with them."