Lost Hansen. (Harold Waldemar Hansen)

Hi, My grandfather, Harold Waldemar, born 1904, had a Norwegian father and a welsh mother. His father's name was Magnus Bertin Hansen who I have been searching for him through a different post "Lost Family in Ibbestad". I am having tremendous difficuty ascertaining my grandfather's nationality since he spent his formative years in Tromso but no official record remains of that period. He has no birth certificate in the UK and no official record of being resident in Norway. Where might I find details of his birth and how could I trace the many sea voyages his father made, between Norway and Swansea, UK between 1901 and 1908. Harold Hansen travelled to UK in 1910 two years after his father died asa result of an accident in Swansea, his father was 33. Harold Hansen lived in wales until his death. Thankyou for your help, Rob Hansen.