This image is of HMS Dreadnought. It is unclear which of the two ships of line that bore this name during the early years of photography this is.
One was a 98 gun ship launched in 1801 which was at Trafalgar but was taken out of commission in 1812 and became a quarantine and then hospital ship before being broken up in 1857. The other was launched as the 120 gun HMS Caledonia in 1808. She was renamed Dreadnought in 1856 when she was made a hospital ship at Greenwich until 1871, being broken up in 1875.
As she was around much later, I tend to think the image is of the former Caledonia at Greenwich.