Knut Kittelson/Numedal River Valley 1854

I am searching for a ship record of Knut Kittelson, wife Tonne Svensdottir and 2 small sons who left Fonnebo farm in Numedal River Valley in April-May 1854 and were in Wisconsin, USA, where 3rd son was born in Decmeber 1854. First 2 sons may have died at sea(?) as no record of them in Bible or in USA. Settled in St. Ansgar, Iowa.