Royal Mail Ship (RMS) St Helena has provided the lifeline service for passengers and cargo to the South Atlantic outpost for 26 years.
However, the vessel is to be sold when its five-day voyages to and from South Africa are replaced by flights when an airport opens on the British overseas territory.
RMS St Helena has travelled 2.5 million miles and carried 101,000 passengers since taking over the route from Cape Town in 1990. She is expected to make the 1,500-mile trip for the last time in July.
Before that, she will make a farewell visit to London in June, sailing under Tower Bridge for the first time.
Her only return visit to Scotland since being built by Hall Russell was a cruise round the Western Isles in the 1990s.
Several potential buyers have expressed interest, with selling agents saying she would be suitable to become a non-polar expedition ship.
The 6,700-tonne vessel can accommodate 156 passengers in 56 cabins, and has a 56-strong crew.
Matt Young, the Scottish chairman of St Helena Line, which owns the vessel on behalf of the island’s government, said: “St Helenians – known as ‘Saints’ – regard the ship as an extension of the island – as soon as they get on board, they feel back at home.
“It’s a very emotional time for them, as they have a great affection for the ship.”
Prior to work on the airport starting, two-thirds of passengers were Saints and one third tourists, who pay some £2,200 for a return ticket.
Direct flights from Luton and Cape Town were due to begin this month with the opening of the airport.
However, this was postponed last week pending further work to mitigate the impact of air turbulence and windshear at the airport.
Edinburgh-based surveyor John Clement, who was a government estates adviser on St Helena until last year, said: “Saints have very fond memories of the ship because it is the source of their connection with the outside world.
“You formed a close friendship with the people you met on the ship which carried on for the duration of your time on the island and beyond.
“It must have the gym with the best views anywhere – a small room behind the funnel with panoramic windows looking back out across the ocean. There cannot be many treadmills where you can do your miles while watching an albatross soar by, or a whale breaching.”
The ten-mile-long island, where Napoleon was imprisoned in 1815, has a population of around 4,000.
It receives £74m a year in UK government aid, which is administered from the Department for International Development’s offices in East Kilbride.