Johan M. Thoresen/William Copeland b. 1834

I am searching any information and even speculations concerning the years Johan Martinius Thoresen from Arendal area spent in the USA. He was born 10. of January 1834 and was last registered in Norway(as a sailor) in 1853. In the late 1850-ies or early 1860-ies he is supposed to have become a U.S. citizen, and he had changed his name to William Copeland. 1864 he emerges in Yokohama and after a while he becomes a Japanese brewing pioner. What happened? What might have happened before he set his feet on Japanese ground? (Even: were there other Norwegian-Americans going to Japan in the 1860-80-ies?)