Can't Find Abraham Thompson of 1864

[?] My great grandfather came to the US and from what I know is he possibly changed his name a little. I know him as Abraham G. Thompson, he was born in Farsund, Norway 8/7/1864 and I hear that he sailed to the US approx 14 years later so that would put it around 1878. He married another Farsund gal by the name of Eilena "Lena" Watney, her DOB: 7/5/1865 They had lots of children and one was my grandfather: Alton Grant Thompson: dob 7/14/1912 in Denver, Colorado. I do not know when exactly he came to the US nor the ship he was on. If anybody can help, I would be greatly appreciated.