There was a Sunderland Flying Boat moored in Southampton Water as recently as the early 90s. I did take some photos of it from Calshot but as they were on 35mm film I haven't found them yet.
What you saw may well have been the Short Sandringham (civil version of the Sunderland) which now resides in the Solent Aviation Museum in Southampton. Interesting aircraft - it has an extra seat fitted on the flight deck. This was installed by a previous owner for his wife........the actress Maureen O'Hara.
I've realised that the reason I couldn't find any 35mm film photos of the aircraft was because I actually shot it on video instead using an 8mm analogue camcorder! The date was the 24/06/90. At present I can only view the footage through the small eyepiece of the camcorder, so I can't see any markings on the flying boat.
The Wikipedia article on the Short Sandringham
https://en.m.wikipedia.org/wiki/Short_Sandringham shows a photo of the aircraft "Spirit of Foynes" moored off Hythe Pier in 1989, which was the approximate location of the one I filmed from Calshot.
Ex-Ansett Sandringham (RAF▸ Serial ML814 Short Sunderland MR5) c/n SH.974b. To RNZAF No.5 Squadron 1953 Fiji and became NZ4108. Hobsonville, New Zealand 1956–1963. Sold 1963 to Airlines of New South Wales. Converted to passenger configuration and registered VH-BRF and named Islander. To Antilles Air Boats, Virgin Island as N158J in 1974. To Edward Hulton in the UK▸ in 1979 as G-BJHS Spirit of Foynes. Storm damaged and repaired. Sold to Kermit Weeks in 1992 and re-registered N158J. On display at the Fantasy of Flight museum in Polk City, Florida, USA with Kermit Weeks and registered as N814ML on 16 September 1993.
This was the aircraft that featured in the
BBC» news video I linked earlier.
I've seen the Sandringham at Solent Sky Museum. According to the following web page:
http://www.aussieairliners.org/shortfb/vh-brc/vhbrc.htmlAIt arived at Calshot, England and beacher for storage - February 02, 1981
Installed in the Hall of Aviation, Southampton - August 27 / 28, 1983
So it was already in the museum when I shot my video.