Thanks.
TITANIC's engineering plant has always been a particular fascination of mine.
Not to be "snarky", but at first I thought you might be referring to some kind of reduction gear(s)... which I was unaware of. Drawings/plans of anything astern of the turbine are hard to come by, and have always been something of a mystery.
To clarify a tad bit further (if I may), here's a bit more on the turbine:
Her turbine was run with exhaust steam leaving her low pressure cylinders of the reciprocating engines (at 9 psi, I believe), not directly from the boilers (which put out well over 200 psi...which would have damaged the turbine...ergo the name "low pressure turbine).
The turbine was used only if the reciprocating engines were working at half-speed or greater. Trying to operate the turbine at lower speeds would have put too great of stress on the turbine and shaft.
The turbine was first and foremost an efficiency thing... like "booster" engine... useful for extracting the last bit of work from the reciprocating engine's exhaust steam and while driving the ship at higher speeds without drastically increasing coal /steam consumption. The turbine's efficiency would do very little for assisting slow speed maneuvering (over the use of the reciprocating engines), even if it was used.
Think of the turbine as a little kid trying to help an adult push a car.
From a dead stop, the kid is practically useless... BUT... once inertia is overcome and the car is rolling, even the kid's tiny contribution can help keep the car rolling, reducing the dynamic effort the adult needs to put out.
Lastly, as 1) the turbine was directly connected to the center shaft/propeller (ie no gearing), 2) the turbine fan blades were specifically designed to increase in size/surface area as the steam progressed thru it, and therefore 3) could only be fed steam in one direction, you could not "reverse" the turbine/shaft/propeller.
Because of all these restrictions to turbine use, the turbine was "bypassed" at speeds lower than half-speed and at any call for a backing/astern bell...and cut out ENTIRELY during restricted maneuvering situations (such as entering/leaving port) where rapid backing/ahead bells might be expected (preventing the engineers from having to constantly cut the turbine in and out). Large bypass valves diverted the reciprocating engine exhaust steam straight to the main condensers instead of feeding the exhaust steam through the turbine.
Cutting the turbine out basically allowed the center screw to "trail" and go along for the ride... LOL.
