Derick was abandoned by has parents when he was a baby. In orc culture if a member is ill or sickly they leave them to their own demise, which is the fate that awaited Derick. Before he could starve Captain Dameian found him and raised him as if he were his son. It was rough living being raised on a ship, but Derick learned how to keep it moving. After years, Derick started wondering what the world looked like and wanted to know more of about the bear spirit that has followed him, so he decided to take his journey to land.
Though this is the reason he gave the crew and his father, the real answer is a bit deeper than he understands. Derick was raised on this ship hearing stories of the world from various crew members or visitors on the ship. He realized that he knew nothing of the world but the stories they shared, so he decided to leave to explore the world and find his own story in it.