Pursuing the Diaphone research, I joined the Gamewell Diaphone Forum. They seem mainly interested in the more modern train/truck horns, but I did get a helpful response from Jim of California – “I would guess from the drawing of the turret that the ship probably had a Type F or F 2T Diaphone. The vertical horn whose picture you found would have been omni-directional, hence the rotating turret might have been redundant (or perhaps for the lights)”.
He does own one of these monsters, but in all the years he has been an enthusiast, he has never seen one for sale. So I don’t think we are going to be able to reinstate the capability!
Having guessed that the hole in the main mast was where the shaft of the light adjusting mechanism went through, it did not take Hercule Poirot to work out that there should be a corresponding hole on the opposite side. Simon investigated and not only found the hole in the mast, but also the hole in the bulkhead next to it.
That hole goes right through the bulkhead, but the blueprints are not clear enough to determine whether the pulley operating the wires/ropes up to the light was in between the mast and the bulkhead, or on the outside of the bulkhead.
Nor can I determine exactly what the wires/ropes do up there at the light.
One other mystery to be solved – directly above where the main mechanism would have been are two pulley wheels set into the roof (sorry, deck). In that position they surely must have had something to do with the light mechanism?
Meanwhile the damn, sorry damp weather is holding up progress. The main deck needs to be sealed and insulated, but is too wet most of the time. This causes condensation and damp below, so the spray-on insulation down there cannot be applied. Realistically I think that is it for the next few months until the warm weather returns, but Simon can get on with finishing the new kitchen and installing some efficient heating upstairs at least.