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