Definitely a merchant seaman. In a later censuses she specifically states Douglas. I only checked 1851 & 1861 census via Ancestry.com
Interestingly, hey first appear in the 1871 Scotland Census (so far!) although they get married in Fife in 1868 (can't find cert.) They got around! Civil registration started in 1855.

Is there another, more thorough resource for 1851/61 census?