From A Wiki of Ice and Fire
A Clash of Kings
Ser Davos sailed the Black Betha north from Gulltown all the way to White Harbor to distribute Stannis Baratheon's claim against the legitimacy of Cersei Lannister's children with Robert I. It returned to the fleet while it was blockading Storm's End.
Black Betha was part of Stannis's fleet that sailed into Blackwater Bay during the Battle of the Blackwater. She and the Lady Marya rammed the Lady's Shame, sinking her. It successfully boarded the White Hart. After the Swordfish rammed the hulk filled with wildfire, Black Betha was engulfed by it and destroyed.