Looking for Iver F. Iverson

Hello, I'm looking for information on my great-great-grandfather, Iver F. Iverson. He immigrated to Chicago (Illinois, USA) from Norway and was living in Chicago by 1874. His profession was a sailor or seaman. I am not able to find any record of "Iver F Iverson" on passenger lists. The only person that is close is Halver Iverson Flaa, somand (sailor), emigrated to Chicago in 1874. http://digitalarkivet.no/cgi-win/webcens.exe?slag=visbase&filnamn=EMITROND&personpostnr=13638&merk=13638 Could Halver change his name to Iver? Any other ideas? Thank you. :-)