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