Hovding to New Zealand 1872

My Great grandparents Anders and Maria Johansen, were aboard the Hovding which left Christiania in May 1872. Also with them was their daughter Louisa (Albertina) whoc was about one year old when they left Norway. How can I find out any information prior to them leaving Norway - their marriage or Louisa's birth for instance. Hope someone can help. They settled in Norsewood, Hawkes Bay, New Zealand. Maybe I have some relatives in Norway who are trying to put the pieces together and we can help each other Thanks