An enslaved Civil War era steamboat pilot, his family and his crew commandeer a Confederate steamer in a daring seven mile open water dash to Union freedom. – Based on a true story.

Since it’s based on an historical person event, I think the logline would benefit by incorporating more specific historical details.? Details that spotlight the risk:? It doesn’t seem particularly dangerous to steer a vessel for 7 miles. The greater danger is that he had to get past 5 Confederate checkpoints. So maybe something like:

The harrowing story of the slave Robert Smalls who in 1862 commandeered a steamer and steered it out of Charleston harbor past five Confederate checkpoints to freedom.

(27 words)