Empire Athelstan was built 1946 and was equipped with three heavy lift derricks.
I worked on her a few days end of 1946 but did not sail in her.
1947 she was sold to Ben Line and renamed Benalbanach - 7795 gt.
1965 renamed Camelot Ministry of Transport and managed by British India Line.
1969 Sold to Mercur Shipping SA Panama and renamed Dragon Castle.
1975 Sold to Soc.Italia Gestioni of Italy and at end of the year was broken up at Split.
There were many tankers with three goalpost masts -many with Empire prefix in names.
I made the maiden voyage in Neritina during 1943 /44 she had them as you mentioned.
Of the tanker in photo I would think she is having the booms and nets removed as it is 1946.
26th June 1945 I joined British Merit at Thameshaven and we sailed for Corpus Christi but called into Falmouth to have the booms and nets removed from the ship.
It was 6 weeks after the war in Europe ended but still at war with Japan..
Outward bound we began to paint the ship in BTC colours which was a very pleasant duty after nearly six years of crab fat grey!!
I spent some time from1961 tp 62 tied up at NEM. They pulled out part of the engine of the Ashburton to realine to shaft. Interesting period of time, not alowed to do any work unlest it was for the safety of the ship. There was a person who walked on board every working day, then sat down in the engineroom to make sure we didnt do anything. If he thought we were doing something over and above safety he left the ship looking for the union. The company was impresed with the NEM performance. I was told that they would never take another ship there.