DSK wrote:

Rick wrote:

One could reasonably assume that the plant was designed to accomodate

Sure, but for how long? It's a liner, designed to maneuver with the aid
of tugs.

As long as it takes to fix the problem. The condenser is large enough to
handle the steam flow required to produce full rated power. The
circulator pump moves more water than is required to remove the heat
leaving the turbine. Reduced power operation might have been required,
just as modern plants - even military plants - but there is no time
limit associated with that condition.

Warships have far greater ability to steam in maneuvers, but at
the cost of efficiency & space. A liner has to make money.

I don't believe wasrships have any exclusive claim to maneuverability
.... that statement applies equally to a warship or a merchant plant. Our
plants are optimized to operate at a continuous maximum power and steam
flow. Anything less is taking life easy on plant at the cost of a slight
increase in brake specific fuel consumption. There are many factors
involved in how fast we go for how long that have nothing to do with the
engine.

... Plant efficiency without the turbine would drop considerably as
the energy in the recip exhaust would be lost to heating the sea.

Right... and this is why I think it would be difficult to maintain
vacuum if you ran without the turbine for any length of time.

The relationship you imply assumes the condenser was sized to require
the use of the turbine ... that simply is not the case. The turbine
allowed the recovery of waste heat at full power. Their is a subtle
relationship between the efficiency of the recips and the cutoff
settings used when operating with and without the turbine online. If
cutoff is extended, as it might have been when turbine was online, the
recips produced greater power but at less efficiency than when cutoff
was shortened so as to allow maximum expansion in the engine.

Maximum expansion of minimum steam (short cutoff) comes at the cost of
wide temperature variations and condensation and re-evaporation withing
the cylinders which is avoided at high speeds and extended cutoff which
leaves more energy in the steam for the turbine to extract.


Don't you think that if the throttleman overdid the reverse steam, it
could damage the crosshead bearings, or the shaft couplings and/or line
bearings, or maybe fold up the prop? Other ships lost prop blades and so
forth at times. The Olympic class props had the blades bolted to the hub
so that the pitch would be adjustable (the ship had to be in drydock for
them to adjust it).

Don't know why it should. The crosshead bearing only "feel" the side
thrust imposed by piston rod movement relative to the connecting rod and
that is a function of load.

Line bearings don't know or care what direction the shaft rotates.

The torque on the shaft instantly changes from driving the prop to being
driven by the prop the instant the throttle is closed. The inertia of
the rotating shaft is absorbed by impeding the inlet of steam from the
throttle to the cylinder. When the force of the steam exceeds the force
of the piston being driven by the shaft inertia the engine will reverse.
The throttle is not opened wide at the same instant that reverse is
selected ... give the operator a little credit for knowing how to
operate the engine. The time involved is very short though, you do not
have to wait until the shaft stops rotating all by itself.

Ships still shed blades and even break shafts ... even though the props
and shafts are designed to function under torgues and stresses that the
engine would never be able to deliver under any and all concievable
conditions of normal or emergency operation.


Rick