Andrew(Andreas,Anders) Solberg and Hanna

I am trying to locate the ship my grandfather came on from Norway. I know it was between 1866-68. I feel it was 1866. He was from Drobak, Norway and his name was Riulf Olai Anderson and came at the age of 8. His parents were Solbergs. I am guessing they went thru Christianna. There were Hans(about 4) and I think Clara was older than Olai and some other children. They went to New York I think and ended at Jefferson Prairie Wisconsin where Andreas died shortly after and then Hanna went to Rollag Minnesota. HELP????? Please. Olai or Ole went by that name rather than Riulf. I heard they probably went in the spring and it was 7-8 weeks sailing. Olai was born 1858.