A stop-and-lock on a turbine plant takes a bit less skill, since all
you have to do is shut of steam on the ahead throttle and crack open
the astern throttle, then slowly open it further. Less things to
break, too.

Nav wrote:
You would not disengage the main gearbox?

How?

... Do you think the main turbine
gets spun backwards by the reversing turbine?

In most turbine powered ships, yes. The propulsion plant is a locked train.


... Two other common methods
are CPP and clutches with reversing gears (the clutches are particularly
interesting from an engineering aspect).

For what kind of plants? AFAIK clutches are quite rare on steam powered
ships. Diesels, yes... provided they aren't using variable pitch props.

DSK

DSK wrote:

Nav wrote:

Skill at the lever. I love it. Don't you know the main engine valve
train was steam operated?


You don't have a clue.

The main engine pilot valves were controlled by a lever which determined
the timing. The position of the lever controlled the duration & timing
of steam admitted to the cylinders and could be set from full power
ahead to full power astern. This was a standard set-up on recip steam
engines.



No, it's you that is full of it. The valve gear was so massive it could
not be moved by hand. Hence my pointing out the steam servo system.

Cheers

Nav wrote:
I know the difference between a vaccumm and and 9 psi! The inlet to the
turbines was not a vacuum Doug!

If you don't believe me, try asking at

http://www.encyclopedia-titanica.org...919/91698.html

Or you could dig up a copy of "The Shipbuilder" magazine from 1911 which
discussed the Titanic's engineering plant in some detail.

Here's a clue- check the designed pressure drop across the turbine...
then look at some specs on operating main condensers...

DSK

Nav wrote:

I'd call it a backpedal when you now admit the inlet was not a vacuum
but at 9 or 11 psi !!! (The latter figure is not in any refs. I've seen.
Where did you get it?))!!!! Now tell us about the bypass valve that's
needed to connect the other engines to the condenser to bypass the
turbine steam path or do you still think the main engines can run with
their outlets closed?

Bwhahahahahah big time I'd say!

You shouldn't have be so quick to Bwahahahahahaha ... when referring to
condenser vacuum, absolute pressure, measured in psia, or vacuum in
inches of mercury are the standard units used.

An absolute pressure of 9 or 11 psia is below atmospheric pressure,
those pressures are said to be a vacuum.

Exhaust from Titanic's reciprocating engines, at a pressure less than
atmospheric, could be directed to the turbine or "bypass" the turbine
and exhaust directly to the condenser. The turbine was used to recover
heat energy from the main engine exhaust which would otherwise have been
wasted, and thereby increase the overall plant efficiency.


Rick

Nav wrote:


DSK wrote:



A stop-and-lock on a turbine plant takes a bit less skill, since all
you have to do is shut of steam on the ahead throttle and crack open
the astern throttle, then slowly open it further. Less things to
break, too.


You would not disengage the main gearbox? Do you think the main turbine
gets spun backwards by the reversing turbine? Two other common methods
are CPP and clutches with reversing gears (the clutches are particularly
interesting from an engineering aspect).

Cheers

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).
For direct drive diesel (majority of ships nowadays) there are no
clutches or reversing gears.

otn

Titanic's turbine specs

Turbine Statistics
Type: Parsons direct coupled LP
Turbine Weight 420 tons
Rotor Diameter 12 feet
Rotor Length 13 ft 8 in
Input blade lengths 18 inches
Output blade lengths 25.5 inches
Operating Pressure in 9 p.s.i.a
Operating Pressure out 1 p.s.i.a
Operating Speed 165 r.p.m.
Operating Output 16,000 h.p.

An apology would be in order, but isn't really expected.

DSK

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

Rick wrote:
otnmbrd wrote:

This becomes an engineering question and I'm not an engineer. However,
considering the mass involved, I'd assume that the process for
reversing engines running at full sea speeds (even recips) would
involve a good deal more than just "throwing a lever" G


Reversing only required pulling one lever to admit steam to the cylinder
of the "reversing engine" which in turn shifted the valve gear to bring
the correct eccentric into play.

Efficient running was something else entirely though, with adjustments
to the valve gear to set the desired "cutoff" of steam to balance
economy vs power.

Rick

Interesting .... thanks. I would have thought, considering the mass
involved that you would have had to reduce "ahead" steam first, prior to
"pulling one lever".

otn

Rick wrote:
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

ROFL Shows ya how far back MY steam experience was !!! Waddahey, I'm a
deckie, I ain't even s'posed to know how to get down into the pit.

otn

Rick wrote:
Exhaust from Titanic's reciprocating engines, at a pressure less than
atmospheric, could be directed to the turbine or "bypass" the turbine
and exhaust directly to the condenser. The turbine was used to recover
heat energy from the main engine exhaust which would otherwise have been
wasted, and thereby increase the overall plant efficiency.

Right... it could be considered a quadruple expansion engine with the
turbine forming a fourth "stage" although it actually had several stages
inside the turbine. It was a reaction type turbine.

One thing I'm curious about is how well they could maintain vacuum with
the turbine bypassed. IIRC the air pumps were driven off the wing engine
shafts. I don't think the Olympic class plants were designed to do
crashback drills.

Regards
Doug King