Photo and details of Black Dwarf (General)
Jo,
from this website for Ships In Port 1881 Census
http://www.angelfire.com/de/BobSanders/81Intro.
I found the following possible ancestor within the Gloucestershire section. I've scanned quickly thro the other likely Ports but found no others, unfortunately the site's search engine seems unwell (I've emailed the site owner for assistance).
Ships at Henbury, Glousester 1881
Vessel: "Squirell"
Henry NELMS M 61 M Berkeley, Gloucester, England Master
Samuel DOWELL M 66 M Berkeley, Gloucester, England Mate
J. NELMS U 28 M Berkeley, Gloucester, England O Seaman