Are you saying that the rudder effrectiveness is not reduced if the
engine is stopped?

Cheers

DSK wrote:

Nav wrote:
Are you saying that the rudder effrectiveness is not reduced if the
engine is stopped?

I'm saying that many of the statements made about why the Titanic hit
the iceberg, with regard to her rudder's ineffectiveness, are incorrect.

As for "engine stopped" that is not a very useful terminology... you
mean shaft stopped & locked? Applying throttle in reverse? Spinning in
reverse with forward way on?

*If* the Titanic's central shaft had been either stopped & locked, or
spinning in reverse with forward way on, then of course her rudders
effectiveness would have been reduced. However neither of those cases
apply for several reasons, the main one being that her central shaft had
no reverse and could not have been stopped & locked.

Regards
Doug King

DSK wrote:

Nav wrote:

Are you saying that the rudder effrectiveness is not reduced if the
engine is stopped?


I'm saying that many of the statements made about why the Titanic hit
the iceberg, with regard to her rudder's ineffectiveness, are incorrect.


Such as?

As for "engine stopped" that is not a very useful terminology... you
mean shaft stopped & locked? Applying throttle in reverse? Spinning in
reverse with forward way on?

*If* the Titanic's central shaft had been either stopped & locked, or
spinning in reverse with forward way on, then of course her rudders
effectiveness would have been reduced. However neither of those cases
apply for several reasons, the main one being that her central shaft had
no reverse and could not have been stopped & locked.



If the engine were stopped the rudder effectiveness would have been
reduced. I think that is most likely true, why do you disagree with it?
If it were reversed, effectiveness would be even lower.

Cheers

I'm saying that many of the statements made about why the Titanic hit
the iceberg, with regard to her rudder's ineffectiveness, are incorrect.


Nav wrote:
Such as?

Such as yours.


If the engine were stopped the rudder effectiveness would have been
reduced.

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.


... I think that is most likely true, why do you disagree with it?

Oh, just a silly whim on my part, no doubt. Years of marine propulsion
engineering have nothing to do with it.

If it were reversed, effectiveness would be even lower.

That's a mighty big "if." As above, please explain how they would have
put the central shaft in reverse.

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

DSK wrote:

I'm saying that many of the statements made about why the Titanic hit
the iceberg, with regard to her rudder's ineffectiveness, are incorrect.


Nav wrote:

Such as?


Such as yours.


If the engine were stopped the rudder effectiveness would have been
reduced.


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.



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


... I think that is most likely true, why do you disagree with it?


Oh, just a silly whim on my part, no doubt. Years of marine propulsion
engineering have nothing to do with it.


So you think an engine in neutral has no effect on rudder?


If it were reversed, effectiveness would be even lower.


That's a mighty big "if." As above, please explain how they would have
put the central shaft in reverse.

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.


Do you know what slip is and how it would affect the rudder? What would
have been a likely value of slip for the central propellor of the
Titanic at full speed?

It's strange but every time I've taken the helm of a displacement boat
the loss of helm authority when the engine is throttled back has been
most obvious. Perhaps it's your engineering expertise that makes the
difference.


Cheers

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?

Another point I'd like you to explain is how do you stop the engine and
not the shaft. Push in the clutch, maybe?


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

No, I'm saying that 1- a ship running at full speed is not going to stop
& lock the shaft in less than a minute, 2- if it did then the water flow
over the rudder would still be quite strong (ie 20+ knots), 3- in the
specific case of the Titanic, the central prop had no reverse and thus
no way to stop the shaft. Did you pay any attention at all to my post
explaining some of the basics of the Olympic class ships propulsion plant?



Do you know what slip is

Yes.


... and how it would affect the rudder?

Sure. Is it supposed to be rocket science? Are you insisting that a ship
going 20+ knots is suddenly not going to answer her helm because of the
loss of the prop stream?

It has been suggested that if the Titanic's central prop had been spun
in reverse, the cavitation would have greatly diminished her steering
response... now that is a stronger case, except that it's simply not
possible when there's no reverse on the central engine.



... What would
have been a likely value of slip for the central propellor of the
Titanic at full speed?

I don't know, but it wouldn't be hard to figure out. The stats for the
engine's RPM and prop pitch are public.



It's strange but every time I've taken the helm of a displacement boat
the loss of helm authority when the engine is throttled back has been
most obvious.

Yes, and I'm sure you have lots and lots of experience driving 800+
ships at 20+ knots. They handle *very* differently than a sailboat with
under auxiliary power.

If you're claiming that a vessel cannot be steered without a prop stream
over the rudder, then how do you manage to control your boat's heading
when under sail?



.... Perhaps it's your engineering expertise that makes the
difference.

Perhaps.

DSK

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 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 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