Captian Andrew G Johnson (b) 1858

Hi, I am a fifth generation San Franciscan, seeking information on my great grandfather, Captain Andrew G. Johnson (b) Oct 1858, Norway.. According to US records, he immigrated to the US (I was told he was a ship Captain) in 1877 (where?), married Elizabeth Forcade in 1885. They had six children, Horace Arnold Johnson was my grandfather. Information on Andrew G. Johnson and his family would be great.[:)]