Thank you Henning for the explanation and of course gwrdave for the picture!

Best regards,

Michael.

https://slideplayer.com/slide/517275/

slide 47

The structures on the top of mast ( C shape ) make sure that the 2 span wires always stay apart. If they come to close you can't control the derrick anymore.
google for "Velle" Derricks or "Hallen" Derrick.
There have been lot's of different designs in the old days

I mean the structure at the top ... looks from a distance like an antenna.

Derrick?

Unusual cargo gear. I have never seen that before ...

Best regards,

Michael.