G. Rennie & Son was founded in 1853, when George Banks Rennie reached the age of 21. Presumably at this time the company of George Rennie and Sons was incorporated.
Partnership change. '...the Partnership hitherto subsisting between the undersigned, George Rennie, John Keith Rennie, and George Banks Rennie, carrying on business as Engineers, under the style or firm of George Rennie and Sons, at Holland-street, Blackfriars-road, in the county of Surrey, and at Greenwich, in the county of Kent, is dissolved by mutual consent, as from the 31st of December, 1861
With the decline of shipbuilding on the River Thames, the Rennies moved to Wivenhoe, in Essex, where he took over the old Forrest Shipbuilding Yard and renamed it the Rennie-Forrest yard, continuing to build river vessels and coasters for the Crown Agents for the Colonies and others until the yard closed 1890
Source: https://www.gracesguide.co.uk
