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Old 08-31-2016, 08:06 AM   #1
Catfish
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Default Managing propulsion, Diesel-electric from another thread

Aktung posted some details on how the german boats were managed. I read that again, and don't understand this. Translation errors? Were the interrogators drunk? This or the engineer told them some serious BS

A chief mechanician prisoner, claiming expert knowledge of Diesels, gave the following explanation of the term "Diesel-Electric."

Ok.

"Diesel-Electric" propulsion is used, when it is desired to put one Diesel out of action for repairs or other reasons, and it is nevertheless required to turn both screws. The electric motors are dual-purpose motors. They can be used either as dynamos or as generators as required. The switching over from one use to the other is done by means of a switchboard and a series of resistances. The whole procedure takes but a few seconds.

Hmm, "used either as dynamo or generator"? Isn't that the same? I would have said could either be used as generator/dynamo or as electric engine. You can switch an electric engine to produce electrical current by switching, and make it a dynamo, ok.
A bicycle dynamo is a generator of energy.

If it is required, for example, to stop the port Diesel and keep under way on the other Diesel, the starboard generator is started from the batteries.

What?
Port Diesel is stopped, ok.
Starboard Diesel runs for getting ahead, ok.
Starboard generator is started from the batteries?
WTH does that mean? Either the generator generates energy to be stored in the batteries driven by the Diesel, or it is used as an electric engine by switching it to engine mode and feed it via batteries.
Any Diesel engine is either started by pressured air, or by an electric engine being run, and then coupled to the Diesel to turn and start it.

The cocks are then shut and the Diesel will run under its own power.

Huh?? Which cocks? What does that have to do with it?

The dynamo is then switched off and the speed of the Diesel increased so that the starboard generator produces enough electricity to drive the port dynamo.

What? The (starboard?) dynamo is switched off and starboard generator produces energy? A dynamo is a generator of energy.

The electricity produced is led through the batteries to prevent the current fluctuating.

Ok, understood. Wherever this electricity .. ahh forget it.

The following table, found among captured documents, would therefore, indicate that if one Diesel is turning at 285 revs. at slow speed and the electric motor is coupled with it, the number of revs. is reduced to 240;

Again, what? If the Diesel runs at 285 rpm and the electric motor (in engine mode, not dynamo/generator mode!) is coupled to, it, it reduces rpms to 240 ???

the electricity produced is sufficient to turn the other screw at 155 revs.

So the energy produced by the starboard engine is enough to power the port electric engine (uncoupled from the stopped Diesel) at xxx revs, without using stored battery energy.

The loss in revolutions is due to the loss of power in the process of conversion.

Ok, got to lose some "johnnies" due to loss in the circuits and conversion.

The differences in speed between port and starboard propellers is counteracted by the rudder.

Seems a bit inefficient, slowing the boat even more. Maybe some translator problems back then, eh?
Or i am beginning to understand how Lucas Electrics came into being
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Old 08-31-2016, 11:26 AM   #2
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Default Misinformation of a defiant nature

Quote:
This or the engineer told them some serious BS
It is entirely possible that the crew was intentionally misinforming their captors. My source was the interrogation report without comment as to veracity by the interrogators. http://www.uboatarchive.net/U-570/U-570INT.htm The date 1941 was early in the war and U-boat crews were not yet demoralized and 'spilling their guts'... lucky to be alive. From the same
report:
Quote:
The chief petty officers, and to a lesser extent, some of the petty officers, expressed great concern at the inadequacy of the training and the lack of U-Boat experience, not only of the men, but also of the officers and petty officers; no attempt was made to disguise the incompetence of the crew and the officers were severely criticised by all the men. The impression gained was that the morale of the ratings was high at first, as they had been filled with clever propaganda about the glammour of belonging to the crew of a U-Boat, and they had little or no realisation of active service conditions; many were helplessly seasick, and, at the first sign of real action, they gave way to panic and became useless, admitting later that they were, in point of fact, glad to be out of the war; they were somewhat childish in many ways and appeared to have forgotten their recent escape from death, as they became interested in and curious about their immediate future prospects. The senior petty officers, having been somewhat depressed from the outset and consequently of lower morale, would have been prepared to put up more of a fight, had they had any confidence in their captain or other officers. The Chief Quartermaster, by far the most competent man in the U-Boat, appeared to have been systematically overworked for many months; he complained that he had only been home on leave once since the outbreak of the war. Like all German prisoners of war captured for many months they were extremely security-conscious as a result of repeated lectures on the attitude to be adopted if taken prisoners. The success of this measure has reduced the information obtained from prisoners and has made interrogation very much more difficult.
@ Catfish: BS is short for ...U-know-what and thus expressly forbidden by FAQ's IN this case! The proper espionage term is Misinformation GEN 'Stormin" Norman Schwarzkopf, himself a master of misinformation, famously got around the BS issue in a press interview..."Bovine Scatology" is however, perfectly permissible!
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Old 08-31-2016, 02:11 PM   #3
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Looks like some translation errors to me. Here is what I think some of the more confusing sentences mean:
=======
The electric motors are dual-purpose motors. They can be used either as motors or as generators as required.


If it is required, for example, to run on only the starboard diesel [while turning both screws], the starboard Diesel is started from the batteries [initially].


The [ignition] circuit is then closed and the Diesel will run under its own power.

The [starboard] motor is then switched to [generator mode] and the speed of the Diesel increased so that the starboard generator produces enough electricity to drive the port motor.

The electricity produced [by the starboard motor in generator mode] is led through the batteries to prevent the current fluctuating [like it would if the starboard generator output was connected directly to the port motor].
============
The last part describes a table which documents the loss of power when running in this configuration, like you suggested with a loss of "Johnnies". :P
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Old 08-31-2016, 02:53 PM   #4
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Ahoi,

i think RentACow got it, found something which sounds similar (port<->starboard)

I found following:
"(Überwasser) langsame Fahrt mit einem (z.B. Bb-)Dieselmotor: Die Bb-Kupplungen sind eingerückt, der Bb-Dieselmotor läuft. Die Bb-E-Maschine läuft als Generator und speist die Stb-E-Maschine, wobei die Batterie als Puffer geschaltet ist. Die Stb-Hauptkupplung ist eingerückt, die Stb-Dieselkupplung ist ausgerückt, der Stb-Dieselmotor steht. Die Propellerdrehzahl ist an Bb größer als an Stb."
Source: Unterseebootbau page 65


I try to translate that:
"Slow-Surfaced only with (e.G.port-)diesel-engine: Both port couplings are engaged, port-diesel is running. The port-E-engine is running as generator and feeds the starboard-E-Engine using the battery as buffer. The starboard main coupling is enganged, the starboard diesel-coupling is disengaged, the starboard diesel-engine is stopped. The port propeller-propulsion is higher than on starboard"

The propellers where close, i don't think that a that 'long' boat needed much rudder to compensate that.

Also they need some Johnnies for the gramophone
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Old 08-31-2016, 03:36 PM   #5
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I would love to hear the whiine of the motors being driven by the diesels as you throttle up to start powering the second screw, so you can get to work on the repairs to the other damaged diesel!
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Old 08-31-2016, 03:47 PM   #6
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Quote:
Originally Posted by Catfish View Post
...
Seems a bit inefficient, slowing the boat even more. Maybe some translator problems back then, eh?
Or i am beginning to understand how Lucas Electrics came into being
mhh...
* diesel runs the propeller with 285revs
* reduced to 240revs when coupled to it's E-Engine as charger
* these lost 45revs are sufficent to give the other propeller 155revs (perpetual motion machine)
* also these 45->155revs keep the batteries charged and produce enough electricity for the other stuff on board

sounds pretty efficient


mhh...
ok, most of the 155-45 = 110 revs came from driving through the water which also produced some revs to the 'more passive' propeller... the more equal the propeller revolutions are, less rudder you need and rudder is nothing else than 'slowing the boat'.

mhh.. conclusion:
it's was more efficient to transfer power from one E-engine to the other E-engine (through batteries) even with electric losses than just to decouple one side completly to let that propeller run 'free' and compensate the difference of the resulting higher propeller-rpms-difference with rudder
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Old 08-31-2016, 03:49 PM   #7
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Ok yes i already thought it makes sense if you exchange the word "dynamo" with motor/electric engine.
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Old 08-31-2016, 04:32 PM   #8
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Quote:
Originally Posted by Catfish View Post
Ok yes i already thought it makes sense if you exchange the word "dynamo" with motor/electric engine.
Make sense of this?! http://www.uboatsim.com/2016/05/24/power-plant-drivetrain/ pg: 140-143.... have pulled specs from the VIIC manual. The main powerplant layout includes two banks of motors, engines, 2 clutches, and the propeller itself....
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Old 08-31-2016, 04:38 PM   #9
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Imagine if one engine is being repaired you must recharge both batteries but the captain wants both screws turning also. You must really give her the beans in order to make any headway. Ahead standard will be a tall order and ahead full speed nowhere in sight! Good luck to future Wolfpack engineers!

Does anyone know how the circuit from a motor acting as a generator was wired to the battery and then to the other motor? did they bridge the port and starboard batteries in parallel? Possibly you could arrange the switched in such a way to run the motors at double their working voltage for more power in an emergency for a short time or on accident and burn out the motors.
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Old 08-31-2016, 05:01 PM   #10
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Quote:
Originally Posted by rentacow View Post
Imagine if one engine is being repaired you must recharge both batteries but the captain wants both screws turning also. You must really give her the beans in order to make any headway. Ahead standard will be a tall order and ahead full speed nowhere in sight! Good luck to future Wolfpack engineers!
Didn't looked yet, but i don't think that the batteries where seperated to port/starboard batteries!? - In that case it would be the scenario like in my post #4 (slow-surfaced with only one diesel-engine, while using the batteries as buffer they also get charged...).

In case both diesel engines have to be repaired:
Maybe, decouple the diesel-engines, both E-Engines switched to charging and get some men to stern on deck of boat; order: "Jump, dive and spin the propellers"

To gain some speed order the rest of crew to the deck on bow and order: "Take the rope, jump and swimm flank ahead"


Last edited by Feldpost; 08-31-2016 at 05:13 PM.
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Old 09-01-2016, 02:02 AM   #11
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Quote:
Originally Posted by rentacow View Post
[...]
Does anyone know how the circuit from a motor acting as a generator was wired to the battery and then to the other motor? did they bridge the port and starboard batteries in parallel? Possibly you could arrange the switched in such a way to run the motors at double their working voltage for more power in an emergency for a short time or on accident and burn out the motors.
Only thing i saw in the U 995 recently was there were switches for a parallel circuit ('Parallelschaltung') and connection in series ('Hintereinanderschaltung'), but i do not know what this referred to..
Max speed at 7/8 knots could not be further improved as far as i know, and it would only be possible to maintain this speed for roughly an hour.

Batteries were not divided laterally in left and right ones, though you could of course bridge cells and remove damaged ones from the circuit if need be.
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