Here's a question.
At what point did they start the center prop when maneuvering this ship clear
of the dock?
Would seem to me, that if they allowed this prop to simply "freewheel" when
maneuvering and they considered the ship to be "good handling" under this
condition, it would counter the statements that the ship was under ruddered.
However, if they would immediately start the center prop when going ahead
during maneuvering conditions, it would boost the assumption that she needed
this prop wash to improve maneuvering or make it acceptable.

Shen

DSK wrote:

Please tell me what ships you've steamed where the engine could be
stopped by "opening a steam bypass valve." Also please tell me where
the steam is bypassed to... are you suggesting dumping main steam
directly into the condenser?


Nav wrote:

On the Titanic the turbine received LP steam from the main engines.


Duh. I told you that several posts ago, Navjax.


Wow I'm impressed! You are a veritable font of information on this
thread aren't you?

.... To stop it separate from the main engines, a valve which I call a
"steam bypass valve" was opened to bypass the turbine and allow the LP
steam back to the condenser.


The inlet to the central turbine was actually under a slight vacuum.


Yopu can wriggle as much as you want but your self serving posturing is
clearly exposed. The inlet to the turbine was not sub atmospheric.

It
wouldn't be "LP steam" it was exhaust from the wing engines. And in
order to *stop* the central turbine, it's steam inlet would have to be
shut.

Wot no bypass valve? Where did the steam go Doug -into the vacuum at the
tubine inlet? Bwhahahahhahaha!! You are such a clown. The inlet pressure
was 9psi -it's on all the web sites describing the engineering -or are
they wrong too?

Cheers

otnmbrd wrote in message nk.net...
Some comments interspersed

DSK wrote:
DSK the marine propulsion expert wrote:

In any case, the ship was going full speed, the loss of the prop
stream across the rudder would not reduce the rudder's effectiveness
very much.

This is probably most notable, in my experience, with variable pitch
props, but you can and will experience it with fixed pitch. You slow the
rpm of the prop and it tends to mess a bit with the smooth flow of
water past the rudder, reducing effectiveness until hull speed reduces
to rpm speed. (personal observation).

I agree.

Nav and Doug missed I think a key part of the story I heard.

That a full astern bell was rung on the port engine to speed the turn.











Nav wrote:

http://www.dellamente.com/titanic/engines5.htm


Interesting web site. Thanks for the link.

It does contain a number of inaccuracies, though.


"Regardless, most scenarios agree steam to the turbine would have been
cut off. While this had little effect on the ship's forward motion,


???

The central turbine was about 35% ~ 40% of the ships forward power. How
is it going to have "little effect on the ship's forward motion?"

Or do they mean that shutting off steam to the turbine would not have
produced significant stopping impulse? That would be much more correct.

They might be thinking that the mass of the ship will keep things moving
with a gradual reduction in speed, not readily apparent in the time
frame of this collision.

They also don't appear to know how the reciprocating engines were reversed.


... it deprived the rudder of the steady, forceful stream of water
necessary to turn a ship of that size.


???

A steady stream of water goin 22 + knots is not "forceful"?

It's forceful, but definitely not as forceful


... Several sources claim the rudder on the Titanic and her sister
ships was too small. If that was indeed the case, shutting down the
center turbine would be the last thing you would want to do in an
emergency."


The "rudder too small" claim is total malarkey. The Olympic was the same
design and had a long service career, with a reputation of being a good
handling ship.

Disagree. Rudder technology has come a long way. Although I don't doubt
that the ships may have been considered good handling by many of the
day, there are many possibilities which could have improved the
"overall" rudder effectiveness, though whether this could have saved the
day, is pure conjecture.


Hmm, seems to agree with me?


Sure. It's incorrect and based on assumptions when accurate data is
readily available.

Speaking of which, have you worked out the prop slip for the Olympic
class ships yet? Data readily available, all you need is the prop pitch,
top speed, and top speed rpm.

Slip is a variable ..... changes from day to day, based on a number of
factors.

... My yacht steers well without propwash because it's rudder, in
comparison, is huge... My point is that, most power vessels can have
much smaller rudders because they use the propwash to significantly
increase rudder effectiveness. It's standard naval architecture.


At low speed, sure. At full speed, the prop stream does increase rudder
effectiveness but I'd say that it's not "significant." Judgement call, I
guess... certainly your vast experience in handling large steam ships
and your claimed naval architect training give you a big advantage here.

DSK


Would disagree. Prop wash is a very important contributor to rudder
effectiveness at all speeds .... put a ship's engine on "stop" ....
trust me, your effectiveness decreases rapidly.

otn

DSK wrote:

DSK the marine propulsion expert wrote:

In any case, the ship was going full speed, the loss of the prop
stream across the rudder would not reduce the rudder's effectiveness
very much.




Nav wrote:

http://www.dellamente.com/titanic/engines5.htm


Interesting web site. Thanks for the link.

It does contain a number of inaccuracies, though.


"Regardless, most scenarios agree steam to the turbine would have been
cut off. While this had little effect on the ship's forward motion,


???

The central turbine was about 35% ~ 40% of the ships forward power. How
is it going to have "little effect on the ship's forward motion?"

Or do they mean that shutting off steam to the turbine would not have
produced significant stopping impulse? That would be much more correct.


Yes, that's what they mean.

They also don't appear to know how the reciprocating engines were reversed.


Why introduce this irreelevance?


... it deprived the rudder of the steady, forceful stream of water
necessary to turn a ship of that size.


???

A steady stream of water goin 22 + knots is not "forceful"?


I expect you don't know this but the effect of wake can reduce rudder
effectiveness. In Titanic's case, the rudder was in the "shadow" of the
hull which further reduced it's effectiveness in the absense of
propwash. The difference in turning circle can be 50% (even at full
speed) for inline rudders. Next time you are out on your tug try it at
full speed -you can measure easily measure your turning circle with a
chart plotter. You increase in turning circle with the prop stopped will
be reduced if you rudder is free of hull obstruction but I'll predict
the difference will be at least 20%. Try it, its an important lesson for
the masters of power vessels -if you want to manouver hard, go to full
power and throw the rudder right over (~30 degrees).



... Several sources claim the rudder on the Titanic and her sister
ships was too small. If that was indeed the case, shutting down the
center turbine would be the last thing you would want to do in an
emergency."


The "rudder too small" claim is total malarkey. The Olympic was the same
design and had a long service career, with a reputation of being a good
handling ship.


Well they are experts but you say they know less than you Doug. I find
your posturing amazing. You have no idea how her rudder area compares to
the accepted norm and yet you say they are wrong. Amazing. In Doug's
world you are always right of course.

Cheers

DSK wrote:

.... At full speed, the prop stream does increase rudder
effectiveness but I'd say that it's not "significant."


otnmbrd wrote:

Would disagree. Prop wash is a very important contributor to rudder
effectiveness at all speeds .... put a ship's engine on "stop" ....
trust me, your effectiveness decreases rapidly.


How about when letting the prop freewheel from full speed?


That does not help. A freewheeeling prop usually takes more energy from
the wake than a stopped prop when the vessel is moving fast.

Cheers

wouldn't be "LP steam" it was exhaust from the wing engines. And in
order to *stop* the central turbine, it's steam inlet would have to be
shut.


Nav wrote:
Wot no bypass valve? Where did the steam go Doug -into the vacuum at the
tubine inlet? Bwhahahahhahaha!! You are such a clown. The inlet pressure
was 9psi -it's on all the web sites describing the engineering -or are
they wrong too?

Actually, they are. The design (according to Harlan & Wolff, who should
know) called for inlet to the turbine at ~ 11 psia. So, if you grant
them 9psi *a* then they're not far wrong. Or are you now going to claim
that the condenser ran at 3 psi ... even back then, hotwell pressure was
usually given in mmHg... hint hint...

DSK

How about when letting the prop freewheel from full speed?



otnmbrd wrote:
Tough question and I don't think there's any ONE right answer.

Well, there are two areas- general ship maneuvering and specific to the
Titanic, which will be somewhat the same and somewhat different ;)

In the case of the Titanic at the time frame between sighting and
collision..... IF they had started to reduce steam to the turbine prior
to reversing the recips, this measured reduction while the other engines
were going full, would/should have created a "disturbance" aft of that
center prop which would/should have reduced the effectiveness of that
single, center rudder.

Yes, but I'm not sure they would have done that. The reciprocating
engines could be reversed with the throw of a lever... the valve gear
control. However there is no definite knowledge of what bells were rung,
when, and how long it took the engineers to answer them. Nor is there
definite knowledge of how long a warning time between sighting the 'berg
and hitting it... the oft-quoted 37 seconds is a figure calculated by
the American Inquiry board from som fairly vague data.

If the steam to the turbine was cut off and the central prop left to
freewheel, then the rudder would have lost some effectiveness... but if
the prop was engaged in reverse (which the Titanic's couldn't be anyway)
then it would be far worse.


Now, since I can see another route to your question. If the ship was
steaming along (different scenario) at full speed with no steam to the
turbine (it's just "freewheeling") would this reduce effectiveness of
the rudder? I would have to say yes, as it becomes a rotating drag which
, in my opinion, has to create disturbed water aft of the prop, which
has to disturb the "smooth" flow of water across the rudder.

Agreed. But I'm saying it would be less than if the prop were engaged in
reverse, or stopped & locked.

Without specific test which address the many various conditions and
actions that where or would occur, you have to assume that the above is
speculation on my part based on my own sense of what has happened when
handling one or two ships. G I.E., I don't guarantee I'm
right....these are my observations.

Well, if you're interested there is a lot of data to look at
http://www.titanicinquiry.org/
has both American and British inquiries and all the testimony.

Shen44 wrote:
Here's a question.
At what point did they start the center prop when maneuvering this ship clear
of the dock?

Hmmm... that is a good question.

Would seem to me, that if they allowed this prop to simply "freewheel" when
maneuvering and they considered the ship to be "good handling" under this
condition, it would counter the statements that the ship was under ruddered.

Another thing that counters the "rudder too small" statements is that
none of Titanic's sisterships were considered under-ruddered. Nor did
they have the rudder enlarged at any point, which would have been easier
to do than the modifications to the Britannic (basically adding a double
hull). The Olympic had quite a long career and was never considered
unhandy... the opposite if anything.


However, if they would immediately start the center prop when going ahead
during maneuvering conditions, it would boost the assumption that she needed
this prop wash to improve maneuvering or make it acceptable.

I think opposing the wing engines would be more effective at low speed,
but of course these things relied on tugs when maneuvering in port anyway.

The ships that I have personally driven were both Navy combatants and
not in the same category as an ocean liner, but they steered about 95%
as well with the prop freewheeling as at normal bells. Of course, a Navy
crew is going to be a bit quicker on the dime answering bells.

Regards
Doug King

DSK wrote:

wouldn't be "LP steam" it was exhaust from the wing engines. And in
order to *stop* the central turbine, it's steam inlet would have to
be shut.



Nav wrote:

Wot no bypass valve? Where did the steam go Doug -into the vacuum at
the tubine inlet? Bwhahahahhahaha!! You are such a clown. The inlet
pressure was 9psi -it's on all the web sites describing the
engineering -or are they wrong too?


Actually, they are. The design (according to Harlan & Wolff, who should
know) called for inlet to the turbine at ~ 11 psia. So, if you grant
them 9psi *a* then they're not far wrong.


Holy backpedal!!!!!!!!!!!!!

Bwhahahhahaha

Cheers

DSK wrote:


If the steam to the turbine was cut off and the central prop left to
freewheel, then the rudder would have lost some effectiveness...

Holy backpedal!!!!!!!!

Cheers

DSK wrote:


In the case of the Titanic at the time frame between sighting and
collision..... IF they had started to reduce steam to the turbine prior
to reversing the recips, this measured reduction while the other engines
were going full, would/should have created a "disturbance" aft of that
center prop which would/should have reduced the effectiveness of that
single, center rudder.

Yes, but I'm not sure they would have done that. The reciprocating
engines could be reversed with the throw of a lever... the valve gear
control. However there is no definite knowledge of what bells were rung,
when, and how long it took the engineers to answer them. Nor is there
definite knowledge of how long a warning time between sighting the 'berg
and hitting it... the oft-quoted 37 seconds is a figure calculated by
the American Inquiry board from som fairly vague data.

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



If the steam to the turbine was cut off and the central prop left to
freewheel, then the rudder would have lost some effectiveness... but if
the prop was engaged in reverse (which the Titanic's couldn't be anyway)
then it would be far worse.

Would require another turbine, but agreed.


Now, since I can see another route to your question. If the ship was
steaming along (different scenario) at full speed with no steam to the
turbine (it's just "freewheeling") would this reduce effectiveness of
the rudder? I would have to say yes, as it becomes a rotating drag which
, in my opinion, has to create disturbed water aft of the prop, which
has to disturb the "smooth" flow of water across the rudder.

Agreed. But I'm saying it would be less than if the prop were engaged in
reverse, or stopped & locked.

True

Without specific test which address the many various conditions and
actions that where or would occur, you have to assume that the above is
speculation on my part based on my own sense of what has happened when
handling one or two ships. G I.E., I don't guarantee I'm
right....these are my observations.

Well, if you're interested there is a lot of data to look at
http://www.titanicinquiry.org/
has both American and British inquiries and all the testimony.

G I've been through much of this in the past, so I've forgotten many
of the specifics, but remember there being many unanswered questions
since their knowledge base was relatively new at the time.
One thing that sticks in my mind was that the turbine received it's
steam from the main recip's which is why I thought they would need to
secure this engine prior to maneuvering the others .....could very well
be wrong here.
At any rate, I'm a firm believer that the Titanic could have benefited
from today's technology on rudders, not only in size but in shape and
location (Hate a twin screw with single rudder).

otn

.... The inlet
pressure was 9psi -it's on all the web sites describing the
engineering -or are they wrong too?



Actually, they are. The design (according to Harlan & Wolff, who
should know) called for inlet to the turbine at ~ 11 psia. So, if you
grant them 9psi *a* then they're not far wrong.


Nav wrote:
Holy backpedal!!!!!!!!!!!!!

Way to go, Navsprit.

I'm right, you're stuck, so you call me names, holler that I'm
backpedalling, and go bwahaha.

I suggest you look at some slightly more sophisticated sources of info.
Not that you'd understand them, but at least you could try.

DSK

otnmbrd wrote:
This becomes an engineering question and I'm not an engineer.

Maybe, but you're a lot more of an engineer than Navvie.

... 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

Oh yeah, it would take a bit of time and some applied skill at the
lever. You *could* just throw it into full reverse, but it would be
dangerous.

I assume commercial ships don't practice stop-and-lock or crashback
drills like a military ship does.

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.
There's the risk of losing vacuum on the condenser (there are far fewer
stages in the reverse turbine) which I assume would not be the case for
a normal recip plant; but would be a potential hazard with the Titanic
because of diverting steam from the central turbine.

When the ship is going slower, it's a lot easier.


If the steam to the turbine was cut off and the central prop left to
freewheel, then the rudder would have lost some effectiveness... but
if the prop was engaged in reverse (which the Titanic's couldn't be
anyway) then it would be far worse.


Would require another turbine, but agreed.

Right... some people think you just hit the clutch and shift into "R"
apparently. ;)




Well, if you're interested there is a lot of data to look at
http://www.titanicinquiry.org/
has both American and British inquiries and all the testimony.


G I've been through much of this in the past, so I've forgotten many
of the specifics, but remember there being many unanswered questions
since their knowledge base was relatively new at the time.

Didn't you used to participate in the alt.history.ocean-liners.titanic
newsgroup? That was an interesting bunch. I seem to recall you and a
couple of other old salts discussing the issue of bringing the
Californian alongside the Titanic.

Anyway, imho the Inquiries are the best primary source of info about the
collision & sinking.


At any rate, I'm a firm believer that the Titanic could have benefited
from today's technology on rudders, not only in size but in shape and
location (Hate a twin screw with single rudder).

Well, her hull was shaped much like the previous generation of sailing
ships. The aft sections would have to be shaped quite differently to
have twin rudders. But Olypmic & Titanic were goreous ships... they
looked like tremendous yachts to my eye.

Regards
Doug King

DSK wrote:


.... The inlet
pressure was 9psi -it's on all the web sites describing the
engineering -or are they wrong too?




Actually, they are. The design (according to Harlan & Wolff, who
should know) called for inlet to the turbine at ~ 11 psia. So, if you
grant them 9psi *a* then they're not far wrong.



Nav wrote:

Holy backpedal!!!!!!!!!!!!!


Way to go, Navsprit.

I'm right, you're stuck, so you call me names, holler that I'm
backpedalling, and go bwahaha.


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!

Cheers

DSK wrote:

otnmbrd wrote:

This becomes an engineering question and I'm not an engineer.


Maybe, but you're a lot more of an engineer than Navvie.

... 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


Oh yeah, it would take a bit of time and some applied skill at the
lever. You *could* just throw it into full reverse, but it would be
dangerous.

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

I assume commercial ships don't practice stop-and-lock or crashback
drills like a military ship does.

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.

Good lord.

For those that have no idea about this here's a site:

http://www.tpub.com/content/fc/14104/css/14104_122.htm

Judge the depth of the Doug BS for yourself!

Cheers

Nav wrote:
I'd call it a backpedal when you now admit the inlet was not a vacuum
but at 9 or 11 psi !!!

Do you know the difference between

psi

and

psia

???

Take a look at any standard marine propulsion engineering text, turn to
the chapter on main propulsion condensers, see if you can find one that
runs at positive pressure.

DSK

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.



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.


Good lord.

For those that have no idea about this here's a site:

http://www.tpub.com/content/fc/14104/css/14104_122.htm

Judge the depth of the Doug BS for yourself!

Please quote the section which you think proves I am BSing. Also, please
quote any references you have saying that the Titanic had clutches. Or
reduction gears, for that matter.

DSK

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

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

Bwhahahhahahaha

Cheers

DSK wrote:

Nav wrote:

I'd call it a backpedal when you now admit the inlet was not a vacuum
but at 9 or 11 psi !!!


Do you know the difference between

psi

and

psia

???

Take a look at any standard marine propulsion engineering text, turn to
the chapter on main propulsion condensers, see if you can find one that
runs at positive pressure.

DSK

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

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.



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.



Good lord.

For those that have no idea about this here's a site:

http://www.tpub.com/content/fc/14104/css/14104_122.htm

Judge the depth of the Doug BS for yourself!


Please quote the section which you think proves I am BSing. Also, please
quote any references you have saying that the Titanic had clutches. Or
reduction gears, for that matter.


C'mon my little fish, you know that you were referring to other turbine
plants -it could not be otherwise unless your decription of a reversing
throtle applies to thne Titanic. OR are you now saying the Titanic had a
reversing throttle?

Man do you love painting yourself into a corner! I guess you don't know
about reversing gears, clutches and CPP's as common ways to give astern
propulsion. OR are you saying all turbine powered ships have a reversing
turbine!

Bwhahahhaha

Cheers

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

DSK wrote:

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.

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.

Recips don't require as great a vacuum as a turbine to operate at their
peak efficiency. Plant efficiency without the turbine would drop
considerably as the energy in the recip exhaust would be lost to heating
the sea.

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

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".

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:
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

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

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


Rick wrote:
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.

I don't think so. There's a volume/temp relationship involved. If you
put steam at a higher pressure & temp into the condenser, at some point
you are going to exceed it's cooling capacity.




... 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.

???

AFAIK there's a time limit, either you regain vacuum and resume steaming
normally, or you don't... and you restrict steam into the engines until
you either have to shut down or you regain vacuum.


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.

No, but warships are designed & built with far less regard to cost and
far greater regard to increased capacity. No merchant ship is ever going
to give up the tonnage & space for such a power plant. For example, a
Fletcher class destroyer's hull was about half filled by it's boiler &
engine rooms.


... 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.

Agreed.


... 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.

Right. But you're assuming that the condenser was enough oversized to
accept all the additional energy from the steam normally extracted by
the turbine. That's my point.

Suppose you took a somewhat more modern plant and installed a pipe from
the crossover into the LP exhaust trunk, shunting exhaust from the HP or
IP turbine directly into the condenser. That would be a similar
situation... and I'm thinking it would be difficult or impossible to
keep vacuum. But after reflection (as I said in my last post), I'm also
thinking it wouldn't matter so much with the Olympics because they would
only have to do this for a short time.




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.

Wouldn't stopping the engine against the force from the prop potentially
create greater loads than normal forward operation?


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

True, but they care a *lot* about compression on the shaft, which is
going to produce axial forces. If you're trying to stop the prop against
the force of water going by, it seems to me you could generate at least
as much compression as if you are trying to accelerate the ship.


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.

But there's more than just shaft inertia involved here... there's the
inertia of the whole ship driving the prop.

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.

Right. That's why I said (quite a few posts ago) that it would make a
big difference having a skillful throttleman on the valve gear lever...

BTW there's a name for this lever, I forget what it is... probably a
Scottish name...

... The time involved is very short though, you do not
have to wait until the shaft stops rotating all by itself.

Right. On the ships I was on, the throttleman who did the best
stop-and-lock drills had bragging rights.


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.

I dunno about "all concievable conditions"... that sounds really
expensive! And remember, back in 1912 engineering metallurgy had not
advanced as far.

Fresh Steam-
Doug King

DSK wrote:
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.


Yes it is -from you! I said the inlet pressure it was 9 psi to correct
your statement that the inlet was at vacuum. You then said I was wrong
and it was 11psi. So you no agree that I was correct all along. Now
let's deal with your other assertion that there was no steam bypass for
the turbine shall we?

You are busted.

Cheers

DSK wrote:


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.


You are contradicting yourself! That means either the old or the new
Doug position must be right but not both. Let me remind you, you said
that I was wrong in stating that there was a steam bypass valve on the
turbine.

I maintain that the bypass valve allowed steam back to the condenser.
Was I right after all? Well?

Cheers

Now as a stream plan expert can you tell us why did they not state the
inlet pressure in mmHg? What is vaccum normally measured in?

I still say the inlet pressure was 9psi! Care to admit I was right?

Cheers

DSK wrote:

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

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.


Yes I know that. It was Doug who said there was no bypass valve. He
seemd to think it was stopped by just closing a valve -but where he
thinks the steam from the main engines would go is anybodys guess.
While the inlet was subatmospheric, the steam would still be passed to
the condensor whose pressures were even lower. I think it's also pretty
sloppy to call the inlet prssure to a turbine a vacuum. Don't you guys
traditionally use mmHg for near vacuum pressures?

Cheers