Umi no Cradle
Set sail in this shipboard drama set in the Age of Exploration from amazing mangaka Nagano Mei. The time is the Industrial Revolution, the location England. Monica, a young girl living in the slums, was making a good living as the nursemaid of Evan, a young child of a wealthy household. But when her master's ship goes missing, she's cut loose. A year later, while visiting his coffin, she happens to see Evan, the child she once took care of. She decides to abduct him and take him away with her on a ship.
(Source: My Anime List)