A prominent collector of marine art who assembled his pictures over a lifetime (his starting point was a gift from his mother), Mr Robertson had spent his National Service in the Royal Navy and, after his return to civilian life, competed for many years in the Cowes to Torquay powerboat race.
The collection as a whole has been estimated up to £1.2m and, being comprised of mainly British pictures, one of the highlights on offer is an interesting historical painting by John Cleveley the Elder (c.1712-77).
The picture shows the arrival of Charlotte of Mecklenburg in England in September 1761. It depicts the Royal Yacht, Royal Caroline, moored off Harwich, Essex. Aboard was the chosen bride of George III, the 17-year-old princess who at the time spoke no English and was to be married a few days later.
Works by the self-taught Cleveley, who was a ship's carpenter at the Deptford Dockyard and, indeed, continued to work as a shipwright well after he embarked on his second career as a marine artist, rarely appear on the market. This one is estimated at £300,000-500,000.
While auction prices of over £150,000 for Cleveley have not been seen since the mid-1990s, the last major sum fetched in the saleroom was for An English frigate under sail firing a gun, which took a premium-inclusive £97,250 at Sotheby's in December 2011.
The sale at Bonhams will be held on July 9.