From A Wiki of Ice and Fire
The Merling King is a Braavosi trading galley.
A Storm of Swords
The Merling King came to King's Landing after the Battle of the Blackwater. There it was hired by Lord Petyr Baelish to take him to the Eyrie to wed Lady Lysa Tully. After putting Petyr and Sansa Stark ashore at the Fingers, the Merling King set sail for Braavos.