1841 census gives born on sea.
I can understand his father being on the sea but why his mother?
Ray
Honestly,all I can do is speculate.
Born on a canal barge or river boat (technically not "at sea", but it could be stated as such)
Born on a passenger vessel (may be unlikely unless the family had money for fares and were moving around)
Born on a deep-sea fishing boat (very unlikely)
Born on a coastal fishing boat or coastal trader (quite possible)
The wife may have been helping the husband earn a living up to the last days of pregnancy.