Looking at the placement of the surface heater on the reciprocating engine room's forward bulkhead (TTSM volume 1, figure 15-3), there's something I can't understand.
The heater drawings from the Board of Trade files give dimensions for the space to be allowed for withdrawing tubes for overhaul, but on the Olympic plans this clearly interferes with the lower deck and casing. They can't be withdrawn inboard either, because of the steam separator.
Would they have dismantled that small area of the lower deck? I assume overhauls would have been infrequent, perhaps once or twice a year.