If he’d been thinking straight, he would’ve switched the ship’s detection system from radar to sonar as soon as they left Charleston Harbor. That’s what he had forgotten. He’d designed the hull to resonate every few seconds, sending waves through the Mist and alerting Festus to any nearby monsters, but it only worked in one mode at a time: water or air.
He’d been so rattled by the Romans, then the storm, then Hazel, that he had completely forgotten. Now, a monster was right underneath them.

The Mark of Athena, Chapter XXI