Turbine vs Reciprocating

[Steffen Reichel]

Dear Charles,
as mentioned before: You haven't to close the throttle. If the linkage is a middle position, not steam can pass the valves, because no valve will open, all set to close position by 0% cut off. At 10% cut off linkage setting, only 10% travel of the piston steam can enter, before valves are closed, ar 20% cut off 20% of the pistons travel steam will enter, and so on.. 100% is impossible, usually 75% was the maximum setting of the linkage, as mechanical frontier.

Also, I mentioned: theoretically one can throw the linkage from full ahead to full astern, as noting really might happen, but there is some mass or weight in motion, acting like a motion wheel still providing power for revolutions in the direction. So changing the direction at once might lead to mechanical overloads, so first the engine had so come below the critical revolutions point, were the direction change can be done without causing mechanical overloads, bending rods or hammering bearings by thrust from the opposite side and creating a brutal force against the motion power left...
But, one point is still in question: Is Titanics propulsion plant need to close the main valve before direction change? For common reciprocating engines it would not be...
As written befor: In several reciprocatin propelled tugboats, it was common duty to switch the linkage form full ahead to full astern without closing the throttle. Paddle wheelers with large, but slow turning reciprocation engines (about 10 or less revolutions per minute) also open main steam valve as brdge calls attention, main steam valve is then opened full ! All other duties are done by linkage adjustment, and the valve no engineers gets in touch, till bridge calls finished with engine.

So I do not knew witch critical revolutiuons Titanics engines had, meaning the revolutions were the linkage can be thrown from ahead to astern, without stopping the engine first... But all I knew, you can, if the meachnical parts can take to load and the bearings too, throw the linkage from ahead to astern without stand still of the crankshaft first...
Because the linkage shut-off the steam before linkage will set to opposite direction. So we have 70% reverse, in middle 0% and then up to 70% ahead cut off. Each percent means this percent travel of the piston the steam can enter the cylinder in the set direction.... So, this means: If you change direction, you have allways a complete shut.off of steam to cylinders first, before the valves were set to the other direction....
But I do not know for Titanic.

 

[Samuel Halpern]

For those interested in technical details on the relationship between cutoff and revolutions, see http://users3.ev1.net/~cfmoore/operating%20systems/engine%20room/asne-1914excerpts/1913standardizationtableIII.htm.

These results are for the USS Texas which had 4-cylinder, tripple expansion engines similar to the Olympic class ships. Notice that at different speeds the steam pressure at the input to the engines were not that different. The steam pressure coming out of the HP cylinder feeding the IP cylinder, and that from the IP cylinder to the LP cylinders did go down but that is due to the changes in cutoff allowing for greater expansion in the cylinders.

 

[Charles B. Weeks Jr.]

Steffen:
I understand what you are saying about switching from ahead to astern without changing the throttle setting. But still momentum equals mass times velocity, so I'm glad I wasn't paying the repair bills. Those engines had a lot of mass and velocity.
Regards,
Charlie Weeks

 

[Noel F. Jones]

Steffen's exposition begs the question:

How was steam excluded from the ahead-only turbine? The reciprocating engine exhausts must have been diverted therefrom and direct into the condensers. This seems to demand some manipulation of a shut-off/bypass valve, either manually or automatic.

Noel

 

[Steffen Reichel]

Dear Charles,
the repair bills depend on the experience and knowledge of the chief engineer. Carefully enginers wait for switching the linkage till the engine had stopped, more experienced engineers will switch the linkage in a moment were the engine is doing just a few remaining rounds, high skilled engineers switch the engine just at the most possible remaining rounds, and brutal engineers just throw the linkage over, regardless of meachanical overloads or material frontiers.
So the carefull engineers cost you, time is labour, and labour is costfully (Because the dampers of the boilers are longer closed, more watter need to be feed to reduce pressure growing up in the boilers.. Grease temperature changes might plug pipes and tubes, etc.) und brutal engineers ruin an engine shortly.
So a skilled engineers is need, because he switches the linkage at the point of shortest time, so steam flow will only shortly be ruptured, and material will have to take a load, but will not suffer damage...
This is why many guys can stoke a marine boiler, and become a good firemen. And good firemen understand the function of the engine, but will never get good engineers. And there are many bad engineers today, less engineers become good, because gathering experience and thus the right feeling for the engine.
I found interesting, that the marine warship was using cut-off of 65% and not less... I thought down to 50% in march speed would be much lessen coal consuption, but i knew the engine not.

But Noel got right, my question makes all other guesses worthless, because the turbine after the reciprocating engines is the point. If the switch take to long, well, then one can also close the throttle, maybe this was need to switch.. Othermise, under which remaining pressure the switch can be done, and how long did this need?
Maybe none need to close the throttle.. I guess the enginer pulls the linkage to middle, to cut off the steam for all pistons. Now the engine will hardly slow down, and another will not do the switch.. After switch is done, from turbine to direct condensator exhaust, the revolution might be that low that the engineers can set the linkage to reverse, slowing down the velocity without material overloads and make the engine going opposite direction nearly a once... How long this would take? I do not knew, all I guess is: Was ist really necessary to close the throttle valve for the engines? From my knowledge, point of view and experience, you need not... But I don't know Titanics engines that good, so be sure that my guess is true or right...

 

[Paul Rogers]

Sam,

Thanks for your detailed response to my question. It has clarified many things in my mind.

Of course, it now appears to me remiss of the Deck Officers not to have put the engineers on standby, knowing that they were probably approaching ice. But that is just hindsight talking... and it probably wouldn't have made a difference anyway.

 

[David G. Brown]

Paul -- preparing the engineers for maneuvers would have changed things in more ways than just adding to the number of men on duty in the engine room. It would have been an acknowledgement of the ice danger and, thus, have required several additional steps. For one, the automatic watertight doors should also have been closed just in case of what did occur. And, the potential need for emergency engine maneuvers would be de facto proof of need for additional lookouts on the bridge wings and the forecastle head. So, not notifying the engineers was simply one of a number of interrelated precautions that were not taken.

-- David G. Brown

 

[Samuel Halpern]

Noel: The changeover valves that diverted reciprocating engine exhaust steam from the turbine to the condensers were of the piston type controlled by a Brown's hydraulic reversing engine like the type used on the reciprocating engines. This engine was controlled from a lever on the starting platform next to the main reversing level.

 

[Paul Rogers]

David -- analysing the situation holistically you are, of course, correct and I had realised that further measures should have been taken. (The wonders of hindsight.) It is true that the Deck Officers did take some precautions however; e.g. the closure of the scuttle forward of the bridge, the warning to the lookouts, etc. so I would not go so far as to say that no-one acknowledged the ice danger. I would suggest instead that the danger was indeed recognised, but was underestimated such that the precautions that had been taken were deemed adequate. (That'll be hindsight rearing its ugly head again, then.)

We are debating semantics here. I will try to be less pedantic in future.

 

[Michael H. Standart]

>>and it probably wouldn't have made a difference anyway.<<

I have some mixed views about that one. My own read of the evidence...and I could be wrong...was that the iceberg took them by surprise, precautions they did take notwithstanding. I would think that having the engineers on the needed stations ready to carry out the needed engine orders might have made for a happier outcome. On the other hand, things might have gone down quickly enough that it would have made little if any practical difference at all.

Unfortunately, as David is constantly...and correctly...reminding us from time to time, history does not reveal it's alternatives. We can only speculate on what might have been if...

 

[Noel F. Jones]

"The changeover valves that diverted reciprocating engine exhaust steam from the turbine to the condensers were of the piston type controlled by a Brown's hydraulic reversing engine like the type used on the reciprocating engines. This engine was controlled from a lever on the starting platform next to the main reversing level.

This seems to suggest there had to be co-ordinated action by two attendant engineers on the control platform. That has obvious implications for the disaster scenario - getting men into position and the elapsing time factor.

One would think that these two manoeuvres would be either co-ordinated by some mechanical linkage or that it otherwise demanded some fail-safe interrupter gear. Surely the one lever could not be operated independant of the other - unless there was a blow-by arrangement by which steam could be contingently exhausted to the atmosphere?

Noel

 

[Samuel Halpern]

The reverse levers for the reciprocating engines had to be independent of each other as well as independent of the lever that controlled the changeover valves to the turbine. These levers could not be couple together for several reasons. First, the turbine was not only disengaged when going astern but was disengaged for all ship maneuvers other than going ahead at one-half or full; i.e., ahead revolutions greater than 50 rpm on both reciprocating engines according to information from Mark Chirnside. Secondly, the reversing levers for the reciprocating engines needed to be independent of each other as well since there may be times that one engine would be put into reverse and the other ahead. The two changeover valves to the turbine/condensers were coupled together on the one reversing engine so that both reciprocating engines exhausted to either the turbine or directly to the main condensers together. However, it should have been possible to reverse the reciprocating engines without necessarily changing the changeover valves to the turbine but that would defeat the purpose of the maneuver since the turbine worked in one direction only. My guess is that the lever that controlled the changeover valves to the turbine would be the first to be changed in any maneuver to reverse the engines which would immediately cut the steam supply to the turbine. Then the reversing gear for the reciprocating engines would be adjusted to first stop and then reverse the reciprocating engines. Also my guess is that with engineers on the standby expecting maneuvers, it would be about 1/2 minute to get the reciprocating engines to stop from full ahead and then start to go astern from time the order was received. Add another 1/2 to 1 minute or so for the engines to be backing hard from that point in time.

 

[Robert T. Paige]

Note to MS: In a previous post, I wrote.:
"Wasn't it impossible to reverse the turbine engine ?" The unexcusable double negative.
Agreed that it should have read.:
"It wasn't possible to reverse the turbine engine ?" -or-
"It was impossible to reverse the turbine engine ?"
Additional question:
"The turbine engine was not in operation during
'in port' maneuvering ?"

 

[Robert T. Paige]

Also have heard that if the turbine engine was stopped (as the reciprocating engines were reversed) the stopped center propeller would have interfered with the rudder action and lessened its effectiveness in the turning process ?

 

[Samuel Halpern]

A stopped central propeller would not necessarily interfere with rudder action as long as there is a slip stream of water passing the rudder. If it did, the ship would be not be maneuverable going in and out of port when the turbine was disconnected. Beside, the propeller would probably windmill in the slip steam. I'm unaware of anything that would actually keep the central prop from turning. I know in a single engine prop airplane you can shut the engine and the prop will continue to turn in the airstream. We actually practice that in engine out training. By the way, the plane is perfectly flyable in that condition. It just becomes a glider.