Unusual Sewells

I am trying to discover more about a William Sewell who was probably born around 1795 and was a 'ship's steward'. He married Elizabeth Barker on the 26th June 1818 in London, and they had at least 6 children:

William Barker Sewell b 1819
Thomas Tokely Sewell b 1826
Joseph Alderton Sewell b 1827
Richard Stout Sewell b 1831
Elizabeth Sewell b 1832
Rachel Mary Sewell b c1834

Despite the use of unusual names like Tokely, Alderton and Stout (which may , like Barker, have been taken from family surnames) I have not been able to find William's birthplace, or much else about him.

Has anyone got a missing piece of the jigsaw?