Hi Kay
Thomas's parents (William and Frances or Fanny) were my 4 x great grandparents. Their daughter Eleanor married Henry Cook. If Thomas was a mariner and cannot be found on the 1841 census, maybe he was at sea when the census was taken. I haven't been able to find Henry on the 1841 census either, so maybe he was a mariner and at sea also. I have a little more information about the family and am willing to share.
Yvonne