Ships to Madagascar

Hi, I would like some help, please, to find out when and how my great grandfather and his family left Norway for Madagascar. Ole Olsen (1835-1911, a seaman/sail maker, born and living in Hetland, Stavanger) left Norway for Madagascar, I think, between 1868 and 1875. His wife, Bertha Marie Sivertdatter, and four children also went there and another three children were probably born on Madagascar. The eldest child, Martha Serine (Olsdatter) was working in Morondava in 1879 and married the missionary Lars Jakobsen Rostvig in 1881 in Tulear, Madagascar. I have not been able to find Ole or the Olsen family on a ship's list. What ships could they have traveled on and how can I find passenger lists to check? I believe that the Norwegian Missionary Society had a ship, the Elieser, traveling between Norway and Madagascar by about 1867. There was also the Vikingen? Could it have been one of these? Karen.