Beautiful photo, Malcolm!
I would guess those D-frames were causing a quite a wear on those cables connecting span tackles with crosstrees...

https://arkiv.dk/vis/4567779

Rick Vince..... Situation was rough due the War in Falklands...Due cargo " Embargo ", the Documents was to Spai.. thence all changed in route and proceeed to UK.... Cheers.

@Carlos, an interesting recollection, thanks, and :
"due situation in Buenos Aires was rough..." rough weather or rough situation due to the war?! :-)

@ Marcin, thank you for those very good photo links. Very nice.
This image: https://arkiv.dk/vis/4567779 clearly shows one of the Hallen's disadvantages; the sometimes acute angles that the pennants on the topping lifts had to endure when the derricks were swung out.

The 'D' frames were there to do just that job, by keeping the two combined topping/luffing sheaves and wires widely apart, but did induce heavy wear to the pennants and 'D' frame itself.
Regards, Rick

Just to add something about Hallen derricks,
Nakskov Shipyard delivered some ships with this interesting equipment, to USSR.
Numerous pictures of details and acceptance trials enable to get closer look:

166 BELORETSK, IMO 5040146, 1962;
http://arkiv.dk/vis/5182877
http://arkiv.dk/vis/4567743
http://arkiv.dk/vis/4567730
http://arkiv.dk/vis/4567779
http://arkiv.dk/vis/5011613

167 BELOVODSK, IMO 5040201, 1962;
http://arkiv.dk/vis/5192301
http://arkiv.dk/vis/4575911

Next two ships of this type were delivered by Burmeister & Wain:
http://www.shipspotting.com/ships/ship.php?imo=5412210
http://www.shipspotting.com/ships/ship.php?imo=5426364

The cargo gear of another pair from Nakskov, 1964, was already modernized:
http://www.shipspotting.com/ships/ship.php?imo=6415245
http://www.shipspotting.com/ships/ship.php?imo=6421402

Rmember during Falklands war... she loaded frozen meat for Tenerife... therefore cargo finaly destination was to UK.... but due to war... cargo destined to Tenerife.. thence change cargo papers says exported from tenerife to UK.... ( vsl call viltoria for fresh water suppy and to take provisions due situation in Buenos Aires was rough...

Also nown as the Hallen Derrick

Commonly known as a 'D' frame.
It's a fixed frame outrigger, which keeps the topping lifts at a sufficiently wide angle to one another to ensure the derrick remains steady even when swung out over the ships side.
It also keeps the derrick(s) stable in all positions, even if the vessel had a list, which they frequently did when loading, albeit mostly minor.
A good idea when designed, with the intention of one man operation of each derrick.
However, they never caught on to any extent.

What is the purpose of those D shape masts on her superstructure?