Scale 1:24. Drawing showing the midships section for the four wooden three-masted paddle steamers of the same class for Cunard (The British & North American Royal Mail Steam Packet Company, Glasgow). These were Britannia (1840), built by Robert Duncan, Greenock; Acadia (1840), built by John Wood & Co, Port Glasgow; Caledonia (1840), built by Charles Wood, Dumbarton; and Columbia (1840), built by Robert Steele & Co, Greenock. The plan also includes details of the fastening methods and ironwork bracing and paddle trusses.

The plan includes the Admiralty Letter Book Numbers S4197 and S11280/56, indicating that these were drawn for, and sent to, the Admiralty. William Blessley was a draughtsman at Portsmouth Dockyard in 1836.