“When her seafaring father goes missing, a headstrong girl who grew up upon stories of the sea, disguises herself as a boy and joins the crew of a Phoenician trading galley to discover clues to her dads whereabouts.”

The pirate idea has all of the above. However, if someone goes missing, most people take the "They'll turn up approach". This lack of concern by others may force her to take action by herself. If pirates take someone, it may be conceived as a threat to the greater community, prompting action - end of story.

There has been heaps of "Saving Dad" stories, Pirates of the Caribbean III, Mullan, Even one of the Indiana Jones flicks had a let's rescue Dad element. The things I find a little misaligned. Is head strong and her actions. Her actions sound more desperate than head strong. I have a head strong daughter (19) she is more likely to carry out overt actions than covert actions. Perhaps my personal experience differs from others,

Good points raised above.

I think that in the face of recent TV shows that deal with similar subject matter in period and cultural. The stakes need to be even hire and the obstacles greater than what is described above.

What if her father was the head of a kingdom (emperor, king, governor, or some other high up politician) her father was ousted by a rival and her family banished. Her father was said to be killed but actually sold to pirates and sent away and she was the only one to have escaped capture. Now it is up to her and her alone to restore her father's power and save the land from the evil rivals.

Other wise I think it would be better to give her a ticking time bomb and raise the tension that way.

After her father was taken by pirates a headstrong girl must assume a male identity aboard a Phoenician trading galley in order to reach her father in time and rescue him from being sold as a participant in a death match.

As mentioned it could be her brother instead and in that case she could be defying her father's instructions when she goes after the brother to add to her burden. Perhaps there is a plot twist by which she learns that the father sold the brother.

Lots of room for play in this idea well done.

Hope this helps.

Also for your consideration, I suggest a variation that intensifies the motivation for the quest. What if it's her beloved (older) brother? The back story is he was forced into indentured servitude by the father who needed the money, couldn't afford to feed an extra mouth. Now there are reports the ship he was on was attacked by pirates.

Now her father bitterly regrets what he did but is to infirm/timid (whatever) to try to rescue him. So she does, to save her brother and right the wrong done to him.

And an additional risk to her is that if she's unmasked by antagonists, she will be sold into slavery, too. Young women, particularly virgins, were even more profitable prime 'meat' for the slave trade. And that is a plot reversal could set up an entire season of harrowing adventure: what she must do when she is outed and sold into slavery herself?

[It seems to me to be too easy for her to be outed by friendly folks who then become allies in the quest. Rather, the stakes and risks -- hence suspense -- must continually escalate. She should succeed the old fashioned way -- earn it every step, every episode by her own wits and courage.]

fwiw