Joseph Sewell a cooper from Crayford Kent / Scotland ?

I have Joseph Sewell in my tree (c.1778/1780-1871). He spends most of his life in Crayford, Kent: I have him there from the 1820s on as his daughter Kezia was born there. However, his birth is given as Scotland (1861 census) and Fife (1871 census). The 1851 census seems to say "on the ocean" but this is not clear. I know Sewell is not a particularly Scottish name but I did find a mention of a Sewell in Alloa on the site if anyone has any more information? Joseph would have been born around 1778-1780. I'm curious to work this one out!

Also would welcome any info on other Sewells descended from Joseph in Crayford, Kent area!

Many thanks.