Steamboats on the river Thames in the 1860's

[The Merry Miller]

In the early 1860's my great great grandfather was an engineer on a steamboat on the river Thames.
 
For a steamboat to have a resident engineer it must have been a biggish boat.
I am assuming from my research that it would have been one of the many paddle steamers operating either up river or down river from Westminster Bridge.

 
Hopefully my next project will be to make a model of the type of engine my gg grandaddy worked on if only I could find out what type it could have been.
Are there any marine engine enthusiasts out there who can give me any help on this?