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

otnmbrd wrote:

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".

Recip engines have to stop before reversing simply because they rotate
in the opposite direction, so do steam turbines. In either case "ahead"
steam is secured since it is pointless and counterproductive to have
steam working on both "sides" of the engine. In the case of a recip, it
is mechanically impossible due to the valve gear geometry.

Admitting steam in the astern direction on a recip changes the side of
the piston which sees greater pressure, this first slows then stops
piston travel ... the forces are the same, the only thing that changes
is the direction of crankshaft rotation.

The turbine is locked to the reduction gear and shaft so it has to stop
before rotation can occur in the opposite direction. There is no problem
admitting steam to the astern turbine while the engine is rotating in
the ahead direction, we do it quite regularly to assist in slowing the
engine rapidly during maneuvering.

Rick

otnmbrd wrote:

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".

Sorry, I neglected one point of your post because it is so much a part
of normal or emergency operation as to require no thought ... of course
the throttle is closed prior to changing direction, no marine steam
engine is routinely started at full throttle. The shaft speed may not
change much when and as the throttle is closed rapidly but closing the
throttle is part of the sequence of operation.

Rick

Rick wrote:
otnmbrd wrote:

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".

Sorry, I neglected one point of your post because it is so much a part
of normal or emergency operation as to require no thought ... of course
the throttle is closed prior to changing direction, no marine steam
engine is routinely started at full throttle. The shaft speed may not
change much when and as the throttle is closed rapidly but closing the
throttle is part of the sequence of operation.

Rick


Thanks. That was/is the point I was looking for.

otn