Are you still looking for information on Thomas Jackman?
There are several records for a Thomas Jackman (and wife Cynthia) that seems to match the parameters you mention, except that he is listed as a "Corn Merchant" in the 1880 US Census, San Francisco.
He and his wife are also listed for the 1871 Washington State Census for Clallam County as well as appearing in the US Census for 1900 and 1910 for Port Townsend, Jefferson County, Washington. There is also a death record for Thomas Jackman from Washington State Death Records , dated 28 October 1910.
I took a look at the ship manifest that you mentioned. It seems possible that Thomas Jackman lists his occupation as "Merchant", rather than "Merchanic.
I hope this is of some help.
Barbara