Tores mailbox VIIC and VIIC/41 operation and technical details

[VIC20]

That's great thank you! I have a lot of patience after all the endless search on the internet before 

[tore]

Mark
The GW engine fuelinjection is controlled directly by the fuel handle on the maneuver stand, thus it is an immediately respond of the engine, a matter of 3-4 seconds from 0 to 350 rpm with engine disengaged from the shaft system. The governor is only maintaining the revs set manually by the fuelhandle and is controlled by centrifugal weights on a shaft driven from the camshaft drive. As the force for moving the fuelrack is not sufficient, there is a linkage from the governor to a slide on a hydraulic servomotor which moves the fuelrack according to the variation of torque to maintain the preset RPM, a detailed analyze of the system is discussed previously on this thread. The servomotor is a delaying element, but only at the variation of torque to maintain a preset revs. I would say a second or two. The variation of torque can be due to inertiaforces like clutching in generator/ E motor, tailshaft incl. propeller or resistance due to generator load or Emotor drive, torsional vibrations and propeller torque due to speed, waves and in shallow waters, depth under the keel etc.
The fuelconsumption for this engine would be between 157 g/bhp and 165 g/bhp, I should assume.
The max continuous rpm is 470, I guess you could run that for hours,  we usually were operating at 460. The overload rpm 490 was limited to a half hours run as far as I remember.
Increasing the rpm to 539 seems to be excessive, we never exceeded 490. By adjusting the linkages you could increase the revs beyond the preset values.
I assume you would have more questions on my answers, so just fire.
Tore

[tore]

Mark.
Supercharger GW engines.
The GW engine is basically a normal aspirated engine which had a booster(Roots blower) driven via a doublecone clutch from the camshaftdrive. At low load and rpm up to 350 rpm you clutched in the blower by moving a handle on the boardside of the engine at the maneuverstand, by doing that you shut off the normal aspirated air inlets and opened for the booster airduct from the blower thereby you increased the airsupply, the bmep and output of the engine by being able to inject more fuel.The interlocks on the fuelrack and the declutching of the blower was indeed executed as you mentioned.
You could run the engine  some 100-150 rpm I guess.
There are different battery chargingloads, starting by not cruising, only charging at very high loads when your batteries were low and very light, just topping up the batteries. As far as I remember the rpm varied with the load I can`t remember the revs. When cruising you put the chargingload according to the requirement of the speed and the timeneed for getting batteries fully charged ,up to the decision of the CO.
Tore

[tore]

Mark
Diesel engine clutch.
As the blowerclutch, the engineclutch was a double cone frictionclutch, the difference being the size and it was pneumatic/hydraulic operated. I guess you could engaged the clutch at 350 revs, but the wear and tear increases with the speed and inertia forces so we usually started with the clutch engaged. Engaging the clutch at relatively high speed created a lot of smoke allthough nobody knew about the asbestos danger, the smoke could be unpleasant in a confined space.
The starting procedure after surfacing was a bit cumbersome, you wanted to get the engine ready as soon as possible in order to exhaustblow the ballasttanks as you was semisurfaced and the  boat was in an unstable position. However you had always some seawater leakages in the exhaust system and some time these leakages could even fill the cylinders. In order to prevent waterstroke, you opened up all the indicator cocks and blow air through the cylinders to get all the water out. Then came the normal starting after shutting the indicatorcocks ,run the engine to some 100 rpm. by air before admitting fuel to the cylinders and ignition. It could take at least 3 minutes.
You question on maneuvering.
After 1942 I guess the GW VII Cs diesels were not direct reversible, the reversing mechanism was removed and the VII Cs were maneuvered by the E-motors only. Direct reversing of a diesel is slow, complicated (expensive), consumes air and is not necessary on a submarine. Most WW2 submarines were maneuvered by E motors. If this is not clear just put forward you questions.
Tore

[Don Prince]

Hello Mr. Tore,


If the crewman was using the wheel-claw tool to operate the gate-valve below deck, then in this instance the wheel-handles were present on the gate-valves.  Perhaps Simon's first drawing was correct after all...


Thanks for the answer about the Q tank missing hand-wheels...


Q tank question - the tank had its internal support structure modified with knee braces to provide support for external pressure.  However, this will not provide for increased internal pressure in the tanks.  This would be a good reason for monitoring the internal pressure of both Q tanks. 


I can think of only two reasons for Q tank to experience increased internal pressure of the magnitude required to burst the tank.


The mushroom valve at the bottom of Q tank were left open after an express.  Now, as the U-boat dives to a greater depth, the water pressure compresses the air in the tank and could causes the tank to burst.   I can see the same situation happening if the mushroom valve were leaking.  I don't believe the venting air pressure could ever cause this problem.


Diving question - as the U-boat goes to a greater depth the actual volume of the pressure hull decreases because of external pressure, and this changes the neutral buoyancy to a negative buoyancy.  Is anything done to adjust for the loss in buoyancy internally like pumping out water from Regulating tank 2?


Regards,
Don_

[SnakeDoc]

Don,

The mushroom valve at the bottom of Q tank were left open after an express.  Now, as the U-boat dives to a greater depth, the water pressure compresses the air in the tank and could causes the tank to burst.   I can see the same situation happening if the mushroom valve were leaking. 

This is not a case - when the flood valve of the negative buoyancy tank is left open or is not tight, the pressure inside the tank is always the same as outside - so there are no forces affecting the tank.

Diving question - as the U-boat goes to a greater depth the actual volume of the pressure hull decreases because of external pressure, and this changes the neutral buoyancy to a negative buoyancy.  Is anything done to adjust for the loss in buoyancy internally like pumping out water from Regulating tank 2?

     
181.  To proceed to great depths (more than 40 meters), the Engineering Officer gives the depth order and the depth changes in increments of 10 meters to all rooms verbally man to man.
         Because the boat loses volume at greater depth, it must be made lighter by timely pumping (for type VII boats approximately 1 ton per 100 meters).  It is appropriate to pump out a greater amount, because the boat will be heavier by the accumulating leak water anyway.

http://uboatarchive.net/DivingRegulations.htm

--
Regards
Maciek

[tore]

Don.
Maciek has answered your questions excellent. I can only add, apart from the depth, the variation in salinity and temperature influence the buoyancy of the boat as well. This can be significant fi. when you are submerged  in a fjord like the very deep Norwegian fjords particularly when the glaciers are melting and freshwater are in layers between the seawater can give you a bumpy ride. However you can compensate a lot by the hydroplanes, but in order to keep the margins you want to correct your buoyancy as much as possible.
Tore

[SnakeDoc]

Maciek has answered your questions excellent. I can only add, apart from the depth, the variation in salinity and temperature influence the buoyancy of the boat as well. This can be significant fi. when you are submerged  in a fjord like the very deep Norwegian fjords particularly when the glaciers are melting and freshwater are in layers between the seawater can give you a bumpy ride. However you can compensate a lot by the hydroplanes, but in order to keep the margins you want to correct your buoyancy as much as possible.

I would add to Tore statement, that although air compressed in the tanks is harmless to the boat construction, but it is highly undesirable due to volume changes along with depth, which results in the changes of buoyancy.
That's why the residual vent of the ballast tank 2 is so important, and that's why, the Germans had special maneuver after submergning the boat - so called durchpendeln. That means slightly trim the boat bow and aft, to remove residual air from ballast tank 1 and 5.

81.  If the flooding maneuver runs normally, the order follows:
         Commander:  "Bring boat to x tons positive buoyancy and put in balance".
         Engineering officer repeats the order.
     
         The boat is brought to a positive buoyancy of approximately 2 tons by flooding the regulating tanks on the orders of the Engineering Officer initially without consideration of the trim.  Now the boat becomes sensitive in longitudinal stability and is oscillated by means of small trim adjustments to purge the residual air from the ballast tanks.
     
         The boat is brought to the ordered buoyancy by further flooding the regulating tanks.  From 2 tons of positive buoyancy the Engineering Officer continually reports decreases in the remaining buoyancy.

http://uboatarchive.net/DivingRegulations.htm

--
Regards
Maciek

[VIC20]

The starting procedure after surfacing was a bit cumbersome, you wanted to get the engine ready as soon as possible in order to exhaustblow the ballasttanks as you was semisurfaced and the  boat was in an unstable position. However you had always some seawater leakages in the exhaust system and some time these leakages could even fill the cylinders. In order to prevent waterstroke, you opened up all the indicator cocks and blow air through the cylinders to get all the water out. Then came the normal starting after shutting the indicatorcocks ,run the engine to some 100 rpm. by air before admitting fuel to the cylinders and ignition. It could take at least 3 minutes.
You question on maneuvering.
After 1942 I guess the GW VII Cs diesels were not direct reversible, the reversing mechanism was removed and the VII Cs were maneuvered by the E-motors only. Direct reversing of a diesel is slow, complicated (expensive), consumes air and is not necessary on a submarine. Most WW2 submarines were maneuvered by E motors. If this is not clear just put forward you questions.
Tore

Thank you! Those two facts are completely new to me.


After surfacing in a dangerous war situation would they have taken the risk to start the engines without blowing possible water out of the engines first?
(OK, I just have to think what kind of situation this could be… possibly makes no sense at all, the only reason to surface while being in range of enemy vessels would be to show the white flag)
I guess the U-Boat can run on E-Machines during this procedure? (or isn't that a good idea without blowing ballast tanks first?)


Then I'll will allow usage of reversed diesel in the game only if the E-Machines are damaged.

I guess you could engaged the clutch at 350 revs, but the wear and tear increases with the speed and inertia forces so we usually started with the clutch engaged.

This makes sense with the information of the seawater leakage in the exhaust system after surfacing. And I think that also means usually E-Machines were shut off until the ballast tanks were blown? Otherwise the shaft would still run at something close to 290 RPM when the diesel is clutched in which is basically the same stress on the clutch just flipped.
So you switched from diesel to electric but usually avoided to switch from electric to diesel while running?






 

[tore]

Mark.
We had our ways and means if a quick start was important, in peacetime f.i.heavy weather. It would take an experienced engineer. Before blowing the tanks (by air)and the mainclutch was still disengaged, running on E motors, you opened the indicator cocks to drain as much water as possible, then carefully admitted air ( low pressure) to the cylinders turning the engine very,very slow to blow out the water all prior to surfacing, then you started the engine as soon as the diesel air inletvalve opened. The procedure would  create some overpressure in the boat and required a very experienced crew for correct timing.  You normally used the E-motors all the time to keep the boat into correct position while exhaustblowing the tanks. When the tanks were fully blown you reduced the E-motor revs and engaged the main clutch and run on diesel.  I think nobody would take the risk of starting the engine without a watercheck as a waterstroke would damage the engine beyond searepair.
Tore

[tore]

Mark.
If you allow the usage of a reversible diesel in your games the relevant boat has to be one of the pre 1943 types, you clearly see the difference of the engine as the direct reversible engine has a dominating vertical reversingcylinder at the maneuvering place forward of the engine see photo.
Tore

[VIC20]

Thanks Tore, it's an early VIIC in the first version of the game.

[SnakeDoc]

To complete Tore's detailed explanations - the German war-time description of G.W. Diesel engines gives following data:
fuel consumption during stationary trials:
overload (1/2 hour), 1612 HP, 494 RPM, 195,5 g/bhp
overload (2 hour), 1515 HP, 486 RPM, 190,2 g/bhp
full load, 1400 HP, 470 RPM, 190 g/bhp
3/4 load 1056 HP, 429 RPM, 187,4 g/bhp
1/2 load without blower, 702 HP, 375 RPM, 182,3 g/bhp
1/4 load without blower, 350 HP, 298 RPM, 197,5 g/bhp

standard revolutions: 470 RPM
highest revolutions: 515 RPM
lowest revolutions (with blower): 130 RPM
lowest revolutions (without blower): 100 RPM

--
Regards
Maciek

[VIC20]

Thanks,    I've just realized you are the one who translated the Type VII manual on Jerry's website to english and Don Prince seems to be the one who had the german original copy.


Any chance that I could I get a copy of the german original? It would be easier to read for me.


I'm currently a bit confused about the engine telegraph and correspondending RPM. Tore said they usual were operating on 460 RPM.
The manual says:



KF = 180.0
LF = 275.0
HF = 340.0
2xHF = 396.0
GF = 435.0
AK = 471.0
3xAK = 480.0


The british report on U570 wrote:



KF = 161.0
LF = 263.0
HF = 310.0
2xHF = 404.0
GF = 469.0
AK = 485.0


Any idea what's the reason for the difference?

[VIC20]

full load, 1400 HP, 470 RPM, 190 g/bhp

hehe, my confusion rises…

The 1400 HP at full load should be shaft horsepower (manual says 1400 SHP, 470 RPM at full load) but the fuel consumption is gramm per brake horsepower.
The manual says fuel consumption of the G.W. is 254 kg/h at full load (470 RPM, 1400 SHP) which is 0.181 gramm per SHP
I think consumption per bhp should be lower than per shp which makes the difference even worse. But actually I have no idea.