Propulsion/steering system

[dude7691]

Hello everyone

I have a question regarding the propeller system on the Titanic. I have been interested in Titanic for many years but I am not a sailor or a ship captain by any means. Now to my question. I am aware Titanic had 3 propellers, two main engines on the port and starboard side and then one steam turbine in the middle, directly in front of the rudder. When they stopped the main outer two engines just before the iceberg collision, did this automatically stop the central propeller as well? I am fully aware it wasn't reversible, but am confused as to whether it can keep turning without the two main engines also spinning forwards. My line of thinking goes that the engines would not have had time to reverse before hitting the iceberg, but surely it would've been smart to keep that middle propeller turning if it wasn't linked to the main engines, in order to increase the wash over the rudder and thus the turning effectiveness. I'm just looking for someone to enlighten me here, as I can't find a straight forward answer anywhere else.

Many thanks

 

[Tim Aldrich]

The exhaust steam exiting the reciprocating engines would only be directed to the turbine engine when power from half ahead and up was ordered from the bridge. Any engine orders below half would have the reciprocating engines' exhaust steam directed right into the main condensers.

Therefore when "All stop" was ordered the steam to the turbine would have been shut off and directed to the condensers. I don't know what the exact equipment was but I would assume there were some huge valves operated by steam cylinders. Sam Halpern has a very good article on Titanic's power plant.

Titanic's Prime Mover

 

[Steven Christian]

On the schematics its labled as a changeover valve. But it doesn't show any steam line going to the valve itself so it could be hydraulic/pnuematically operated if not steam. I would need to see more detailed schematics with the control system. I'm not seeing the main steam blowoff valves either. You would think if they went from full ahead to full stop and and the main stop valves slammed shut the relief valves would be triggered automatically. Maybe on a relatively small and low pressure system like Titanics you could operate that way. I dont know. I need to go look at the control system more. And when I say Titanics system was small I don"t mean that as a ding against her. I find the systems and machines of those days facinating.

 

[Stephen Carey]

The change over valves were operated by "Brown's Engines" a very popular method of operating large valves back in the day.
Apparently the Olympic Class did have a "Silent Blowoff" whereby excess steam was sent direct to the condensers, though I have found no other evidence for it. That the boiler safeties lifted is beyond doubt as I believe many mentioned it (as shown in the Cameron film). The massive volume of steam in firetube boilers fired by coal has to go somewhere and it's usually via the safeties.
Modern steamships per gas carriers may have a silent blowoff, though how silent it actually is I don't know. It's usually accompanied by a desuperheater and a condenser spray to avoid destroying the condenser vacuum.
If anyone has info on Titanic's silent blowoff, I'd be interested to see it.

 

[Steven Christian]

The change over valves were operated by "Brown's Engines" a very popular method of operating large valves back in the day.
Apparently the Olympic Class did have a "Silent Blowoff" whereby excess steam was sent direct to the condensers, though I have found no other evidence for it. That the boiler safeties lifted is beyond doubt as I believe many mentioned it (as shown in the Cameron film). The massive volume of steam in firetube boilers fired by coal has to go somewhere and it's usually via the safeties.
Modern steamships per gas carriers may have a silent blowoff, though how silent it actually is I don't know. It's usually accompanied by a desuperheater and a condenser spray to avoid destroying the condenser vacuum.
If anyone has info on Titanic's silent blowoff, I'd be interested to see it.

You can see the silent blow off valve and lines on some of the diagrams in the article below. Also there is a desciption of how they were used. I haven't seen Camerons movie in a long time now but if I remember right the safeties didn't open for a while. I would have to see the control system to know why. On the system I worked on there were different kinds of "trips". If it was a turbine/generator trip the stop valves would slam shut almost instantaneously and the main ERV's would open. They were so loud we would get calls from 5 miles away because they thought the plant had blown up.

Titanic's Prime Mover

A detailed examination of Titanic engine room and boilers, with schematic illustrations and photographs.

www.encyclopedia-titanica.org

 

[Stephen Carey]

Thanks for that Steven, it's cleared up something that's puzzled me for a while, even though I've read Sam's description more than once! So it seems that the Silent Blow Off was to regulate the steam pressure to avoid the safeties lifting when the fires were banked and awaiting a telegraph movement. It wasn't designed to relieve the steam from all 24 boilers banging away at full chat and 22 knots, which was why I questioned it in the first place, and why the boiler safeties all lifted after the crash stop of the main engines after striking the berg. All that steam has to go somewhere, and the size of the piping of the silent blowoff wouldn't allow it, along with it just about wrecking the condenser (as mentioned in Sam's description). I have worked on designs where a "steam dump" has been used on TG applications in the oil and gas industry (using a desuperheater and condenser water spray), and this is included on LNGC power plant. For crash stop of main engines at Full Away though, the boiler safeties are going to lift come what may.
As for a control system, the Olympic Class didn't have one per more modern steam plant - it was all manual. I believe even the boiler water levels were manually controlled at the time; there's no mention of a boiler level controller in the books on the ships. And yes, safeties are noisy, especially on a superheated system at 60bar, 512°C...

 

[Steven Christian]

Thanks for your post I liked it. We didn't really have anything that was called silent blowoff but in effect it was probably the same thing. Our two main trip schemes were turbine generator and boiler trip. A TG trip everything slammed shut and the safeties lifted. A boiler trip would let system roll down so to speak. Steam was allowed to condense in the hotwell, feedwater heaters..ect. So I guess that during a boiler trip it would be somewhat analogous to using a silent blow off. Condensate was expensive to make so it was best to save as much as you could. We were a super critical system and our condensate was less than one part per billion solids. It took a lot to make it. You stated that most of Titanics system was run in manual. In that case I have even more repect for Titanics engineers and crew. Toward the end of my career a lot of the new control operators were downright terrified to run stuff in manual. It became a point of contention. A lot of times I would tell my boss.."this isnt isn't going to get done tonight" "Why"..so and so ons shift tonight, he won't go to maual so I can work on it. Usually followed by a stream of profanity..LOL. But the older Control Operators it was no problem.

 

[Steven Christian]

I have some question for any of you that are familar with ships turbines and engines. I've never worked on any. Never really even seen any except for small engines on museum ships. I did have to crawl down one of the shaft alleys on my aircraft carrier once. But that was just to stand fire watch while a welder scared the crap out of me...*L*. 1. When the valves were closed to the turbine did the the turbine freewheel when the ship was moving? 2. After the ship had set awhile with the engines off did they have to pre roll the shafts in some way? I ask because on our turbines after they set offline awhile when had to put them on turning gear at 2 rpm for 24 hrs to get the shaft bow out of them...otherwise we would wipe the bearings. Or was none of that a problem on ships? Have wondered about that before.

 

[Alex Clark]

Is shaft bow when the shaft sags under its own weight?

 

[Steven Christian]

Is shaft bow when the shaft sags under its own weight?

Yes. It was a problem on the big turbine/gen sets I worked on but don't know if was a problem with ship turbines. When ours set offline for a while we had to put them on turning gears and rotate the shafts at 2 rpm for 24 to 48 hours to get the bow out. Online they would run at 1800 (4 pole gen) and 3600 (2 pole gen) rpm. We had eccentricity measuring devices that would tell us when we were good to go. I was curious if that was even a problem on ships and how they dealt with it. It might not be a problem with smaller turbines especially if the bearing points are relatively close together. The only solution I could see was to run the ships turbine at lowest rpm for awhile if it even was a problem.

 

[Georges Guay]

I have some question for any of you that are familar with ships turbines and engines. I've never worked on any. Never really even seen any except for small engines on museum ships. I did have to crawl down one of the shaft alleys on my aircraft carrier once. But that was just to stand fire watch while a welder scared the crap out of me...*L*. 1. When the valves were closed to the turbine did the the turbine freewheel when the ship was moving? 2. After the ship had set awhile with the engines off did they have to pre roll the shafts in some way? I ask because on our turbines after they set offline awhile when had to put them on turning gear at 2 rpm for 24 hrs to get the shaft bow out of them...otherwise we would wipe the bearings. Or was none of that a problem on ships? Have wondered about that before.

In Titanic’s Prime Mover - An Examination of Propulsion and Power study analysis by Samuel Halpern, it is written; «The changeover valves ahead of the turbine did provide some form of speed control as there was an automatic override whereby the turbine's Proell centrifugal governor actuated the Brown's engine used to operate the two piston changeover valves. If the speed of the turbine rotor exceeded 10% above the maximum number of revolutions dialed in, the changeover valves would redirect steam to the condensers until the speed of the turbine dropped below the preset limit.»

I would tend to say that the engineers steamed pressurized the Parsons’ Direct-Coupled Low-Pressure Reaction Turbine via the Proell centrifugal governor just enough to make the turbine turning a few rev's as you said, thus the center propeller as well. The system was most probably equipped with a mechanical turning gear and a locking system for the propeller maintenance. But I am not too sure they were locking the shaft while underway. Note that a freewheeling center propeller would produce less cavitations thus enhanced water flow to the rudder, but more drag.

 

[Steven Christian]

In Titanic’s Prime Mover - An Examination of Propulsion and Power study analysis by Samuel Halpern, it is written; «The changeover valves ahead of the turbine did provide some form of speed control as there was an automatic override whereby the turbine's Proell centrifugal governor actuated the Brown's engine used to operate the two piston changeover valves. If the speed of the turbine rotor exceeded 10% above the maximum number of revolutions dialed in, the changeover valves would redirect steam to the condensers until the speed of the turbine dropped below the preset limit.»

I would tend to say that the engineers steamed pressurized the Parsons’ Direct-Coupled Low-Pressure Reaction Turbine via the Proell centrifugal governor just enough to make the turbine turning a few rev's as you said, thus the center propeller as well. The system was most probably equipped with a mechanical turning gear and a locking system for the propeller maintenance. But I am not too sure they were locking the shaft while underway. Note that a freewheeling center propeller would produce less cavitations thus enhanced water flow to the rudder, but more drag.

Ok thanks for that reply. I was wondering if it was an issue and how they would control it being that the prop is directley connected to the shaft. I had to go look up the Proell governor as I wasn't familar with them. A more advanced flyball governor. Interesting. I'm sure they must have had some kind of locking system like you said but don't know if was a typical jacking gear or something else. There's a pic of a jacking gear in the link below. Maybe it was something like that. Thanks again for the info.

What is Proell Governor? How does it work? - ExtruDesign

To make the Proell Governor more sensitive, we will extend the links upward to support the revolving balls. It is one of Centrifugal Governor type.

extrudesign.com

http://navy.memorieshop.com/Cargo-Ships/Engine-Room/POWER-TRAIN-Profile.html

 

[Steven Christian]

Well if this post is correct then I guess ships did have a problem with shaft bow. It's post #10 from the thread below. The relevant line from the post states "otherwise you will have problems with the turbine shaft as it will bow and bend or as it is correctly termed hog and sag".

Restarting Titanic's Engines

There's a bit of evidence that, after the collision, Titanic's engines were stopped and then briefly run again. (I know, it's all very vague) A little bird in what passes for my brain keeps telling me that somewhere I've heard a perfectly sane reason for this. I can't place the source. It...

www.encyclopedia-titanica.org

 

[Stephen Carey]

I have some question for any of you that are familar with ships turbines and engines. I've never worked on any. Never really even seen any except for small engines on museum ships. I did have to crawl down one of the shaft alleys on my aircraft carrier once. But that was just to stand fire watch while a welder scared the crap out of me...*L*. 1. When the valves were closed to the turbine did the the turbine freewheel when the ship was moving? 2. After the ship had set awhile with the engines off did they have to pre roll the shafts in some way? I ask because on our turbines after they set offline awhile when had to put them on turning gear at 2 rpm for 24 hrs to get the shaft bow out of them...otherwise we would wipe the bearings. Or was none of that a problem on ships? Have wondered about that before.

On any ship that is at "Full Away" - motor or steam - the shaft will freewheel under the impetus of the ship's momentum. Here's a scenario from one of my answers on Quora - Why didn't Titanic just reverse its engine when it saw the iceberg? - Quora
As you can see, it's not something that you want to happen every day, and stopping the screw "windmilling" is the same on every ship. Warships often have a shaft brake however, which will stop the shaft and enable astern running much faster. Merchant ships are not really designed for crash astern movements at full away - they'll do it, but not too often thanks!
On steam turbine ships we had turning gear which was engaged in port to turn the engines every so often by one and a quarter turns. This was to ensure the turbine rotor didn't end up in the same place and "sag" under its own weight. On standby and warming through, awaiting bridge telegraph orders, the engines were on "steam swinging" which on the older ships of my youth meant one of the Juniors standing at the starting platform and cracking the ahead and astern valves open, swinging the engines ahead and astern to keep them warm and avoid sagging. On more modern steamships (not many left these days) steam swinging is done by the automation - another Junior's job gone!
Sagging can ruin your turbine as the rotating blades come into contact with the stationary ones, and a permanent "set" will spoil your day.
On a motor ship, the same thing was done, though the "one and a quarter turns" wasn't really necessary. We would work the cylinder lubricators to oil the piston rings at the same time, and sometimes have the main lub oil pump running whilst the engine was turning on the gear. The idea in motor ships was not crankshaft sag, but to avoid the rings marking the liner walls, and oil running out of the bearings. In port the main engine would be turned once per watch.

 

[Steven Christian]

Thanks for that reply. Everything you said makes perfect sense to me. A little pre maintenance/operations can make a big difference. We found over the years that on our large aux ac motors that sometimes set for months it was best to have them rotated a quarter to half turn periodically to avoid getting flat spots on the ball bearings. Helped a lot. A sore spot with me these days is car manufactures say with the modern engines there's no need to warm them up...just start and go. I don't buy it. My wife would get upset because I would make her count to 30 before putting her car in gear. At least let the oil circulate before putting a load on the motor. Of course her other bad habit made her one of the lowest life forms on the planet to a gear head...she was a clutch rider...