The structure on the right of Colin's photo is the trunking for an aerial lead-in insulator. The ship's main transmitting aerial would have been strung between the foremast and the mainmast. A downlead would have been spliced part way along it to form a "T" or an inverted "L". The end would have been connected to the insulator on top of the trunking. In the photo the wire goes off to the right so it probably goes via another insulator to take the strain and/or route it to avoid the radar scanner. A copper tube will connect vertically down from the lead-in insulator into the Radio Room below where it would go to an aerial selector unit and thence to the Main or Emergency Transmitters. All this stuff is long gone from the ships of today but I was on a very old ferry some years ago, the "Stena Searider," and took the second photo above showing the monkey island on there. You can see a disused lead-in insulator on the far right of the photo, the trunking being white painted steel.
Colin's photo is probably taken from the Bridge wing looking aft at the funnel. The tall white structure behind the person in the photo, with a mast rising vertically from it, makes me suspect that this may be the S.S. "Canterbury," as seen in the third photo. This is a British Railways photo so it is post 1948 and she has been retrofitted with an early merchant ship radar. The transceiver took up a lot of room and had to have its own housing as shown. The stub mast above it has the scanner on top although it is side on in the photo so you cannot see it. The stub mast was high enough for the scanner beam to clear the funnel and not leave a blind sector astern.