Maggie and the Pirate’s Son by Rose Prendeville

Once upon a time, Maggie Mackintosh Budge yearned for handsome rogues and breathtaking adventure. Now widowed after a disastrous marriage and desperate to escape her still-matchmaking father, she stows away on the nearest vessel because sometimes the only solution is running away to sea.
Bastian MacLeod never chose a life of piracy, but after coming of age under the brutal regime of Auldfarrand’s Revenge, his world has been limited to placating the volatile captain and staying one step ahead of the navy—that is until he discovers Maggie in the cargo hold. The first rule of piracy is: wenches are unlucky and will be cast overboard.
With Bastian’s help, Maggie disguises herself and joins the crew, but sparks between them ignite like St. Elmo’s Fire. Can they keep her secret—and keep their hands off each other—long enough to outwit the navy and hunt down the captain’s lost treasure? Or will bad luck send them both to the hangman’s noose?