Maybe I can help a bit. I was in the Canadian Navy from '68 to '73, long time ago now...... The St. Laurent types that we had then were steamers - two boilers and two main turbines. One boiler room watch would consist of two burner tenders, one water tender and the Petty Officer of the watch. The Engine room watch was a roundsman for outside machinery (steering gear, shaft bearings and stern glands, etc),an inside roundsman, throttle watchkeeper, and the Chief of the watch. Each Chief of the watch reported to the Chief ERA, who reported to the Engineer Officer, who reported to the Captain. There were other ratings in the department who were usually day workers - Upper Deck Stoker (responsible for fuel, ballast, domestic water, pumping systems), Evaporator watchkeeper, Engineer's writer, and usually two outside machinery people to lok after HVAC, refrigeration, emergency generators, and assist anywhere they were needed.