Beneath the Waves — J. Kathleen Cheney

Cristiano Tavares and Emilia Atkinson have been working for years to perfect the newest experimental craft for the Tavares Boatworks: their first submarine. The government is offering a contract to the boatmakers who can prove their worthiness by winning a race from Lisboa to the Golden City. It's perfect timing for the boatworks. They just need to get into the water. They have the best boat, a determined crew, and even a sereia to help guide the boat underwater. But someone else has other plans for the race, and their simple quest to get from one place to the other may end up leading to their deaths....