We are talking about the central shaft OZ. Please keep up.

Cheers

OzOne wrote:

On Thu, 30 Sep 2004 11:03:22 +1200, Nav
scribbled thusly:



The engine would be stopped by opening the steam bypass valve. That
might not stop the propellor but that's not the issue here.

Now are you still saying that stopping the engine has no effect on
rudder effectiveness


Hey now that would depend on which one of the three was stopped.


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.

Nav wrote:
We are talking about the central shaft OZ. Please keep up.

Actually, I think he's gotten the point more quickly than you seem to be
catching on.

DSK

DSK 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.

DSK

I agree 100%.

But if a full astern bell was rung then the induced wheel walk could
of forced her stern to swing faster into the berg.


Joe

DSK wrote:

OK, tell us what you mean by stopped. Then tell us about the
Titanic's engineering plant and how they would have "stopped" the
central shaft.


Nav wrote:

The engine would be stopped by opening the steam bypass valve. That
might not stop the propellor but that's not the issue here.


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?


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

It is strange that you claimed such expertise on the Titanic machinery
but did not know this.

Cheers

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.



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

"Regardless, most scenarios agree steam to the turbine would have been
cut off. While this had little effect on the ship's forward motion, it
deprived the rudder of the steady, forceful stream of water necessary to
turn a ship of that size. 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."

Hmm, seems to agree with me? 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.

Cheers

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.

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"?


... 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.


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.

... 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

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.

.... 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. 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.

Then what happens?
hint- consider the relationship between the seawater inlet temp to the
condenser (termed "injection") and the condensing pressure of steam
going into the condenser.


It is strange that you claimed such expertise on the Titanic machinery
but did not know this.

Strange that you are now repeating my posts, ignoring proper
terminology, and basically showing total ignorance of steam propulsion
engineering, while insisting that somehow I'm the one that's wrong.
Actually, it's more funny than strange, and also par for the course.

DSK

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).





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

.... 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?

DSK

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?

DSK


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

otn