otnmbrd wrote:

In my experience, with pure steam turbine plants, if you are at "sea
speeds", to stop the HP turbine you first have to pull out the extra
nozzles, then shut down the steam, then open the "guarding valve", and
when the shaft has stopped or nearly so, you can start cracking steam to
the LP turbine .... not the quickest of procedures.
There are no clutches or methods to disengage the main gearbox
(reduction gears).

Steamboats have not used manually controlled nozzles for many years. The
modern turbine throttle valve uses a lifting beam to sequentially lift a
set of nozzle valves in the steam chest. A hydraulic cylinder lifts the
beam under control of the console throttle lever or wheel in maneuvering
mode or an electronic speed control when at sea speed.

The guardian valve may be operated remotely at the console and may be
selected to open when the throttle is moved astern. The engine does not
have to be stopped before opening the astern throttle and crash stops
are routinely performed after majopr maintenance or shipyard work on the
control system.

Rick