Rick wrote:
One could reasonably assume that the plant was designed to accomodate
the loss of the turbine and the condenser could operate at the vacuum
required to allow full power from the recips.

Sure, but for how long? It's a liner, designed to maneuver with the aid
of tugs. Warships have far greater ability to steam in maneuvers, but at
the cost of efficiency & space. A liner has to make money.


Recips don't require as great a vacuum as a turbine to operate at their
peak efficiency.

I guess you could run them with the exhaust vented up the stack, like a
railway locomotive. But you'd run out of feedwater after a while!

... 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.

Recips could and would crash stop quite well, all ships are designed
with emergency backing in mind.

Sure, that's their "brakes."

Thinking a bit more on the issue, it doesn't seem that an Olympic class
ship would ever need to keep up vacuum with the turbine bypassed, any
longer than the minimum needed to maneuver in and out of port, and to do
*one* crashback.

With regard to the Titanic specifically, it's not certain what bells
were rung or if they were answered before the collision. If Murdoch
really did ring up full astern, it's barely possible that could have
been enacted before the crash. IIRC the surviving stokers said that EOT
bells weren't rung up until after the collision, and some said it was a
"Stop" not a "Reverse" bell.

... A recip will generally stop quickly due
to the internal friction but steam can be admitted in the reverse
direction without harm ... it is a compressible fluid and acts as a
cushion in normal operation. Reversing is a simple matter of changing
the operative eccentric, all tghe parts move in the same plane as
before, only shaft rotation, thrust, and crosshead guide thrust changes,
and the engines are designed with that in mind.

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).

Anyway, my experience with recprocating steam engines has all been on
much much smaller machinery, some of it from that era and some even
earlier

Regards
Doug King