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

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

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

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:


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

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