Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,


My wife Maureen and I have been talking about visiting the U-995 Museum and other parts of Germany next year because some of her Asian college friends live in Germany as well. I would like to visit Berlin and get together with Mark Hessburg, and even perhaps visit Norway and actually meet first hand with my friend and colleague Mr. Tore Berg-Nielsen...


Regards,
Don_

[Raymic1]

Make sure you contact Mr Paul Patrick-Schroder. A curator at U995
I believe he assisted you with the Uboat files?.
He has been very helpful to me also.
Be great to get a tour into the Tower.


But its closed at present to Covid.

[tore]

Don.
You are welcome, hopefully the Covid 19 restrictions shall be lifted. I donated some images from U-995s life in Norway to the museum.
Regards Tore

[VIC20]

Great, would be nice to meet you Don.

[Don Prince]

Hello Mr. Tore,

I believe you have been copied on the email schnorchel discussions the past month or so with Simon. Arron S. Hamilton's book "Total Undersea War" has a great deal of info about the schnorchel and procedures. I was reading through some of what is available online (I just ordered the book on Amazon) and I have a few questions related to starting the GW Diesel engine...

1. They bring the U-Boat up to 25 meters and raise the schnorchel, then continue up to attack periscope depth.
2. The schnorchel head is above the water and then the Schnorchel air supply shut-off valve is opened and the water in the schnorchel air supply tube is drained into the bilge.
3. The internal exhaust valve is opened to enable schnorchelling and the blowing valve for the selected diesel engine is opened to direct the exhaust gases to the schnorchel.
4. The GW Diesel engine is started with air...

Now, here is where your expertise is needed:
When the GW diesel engine is running on air, how long is it before you switch over to running on fuel oil? I believe the internal air pressure in the GW diesel exhaust system will start to build up at a fairly rapid pace. Therefore, they need to monitor the exhaust air pressure, and open the schnorchel exhaust shot-off valve at the appropriate pressure to blow out the water in the schnorchel exhaust side (something like blowing the ballast tanks). I doubt if the schnorchel exhaust blowing is done while the GW diesel engine is running on fuel oil...

Q1 - How long will the GW air startup normally take?
Q2 - The book stated that the GW supercharger and the MAN turbocharger must both be turned off while schnorchelling. I thought the MAN turbo charger was constantly running?

Regards,
Don_

[tore]

Hello Mr. Tore,

I believe you have been copied on the email schnorchel discussions the past month or so with Simon. Arron S. Hamilton's book "Total Undersea War" has a great deal of info about the schnorchel and procedures. I was reading through some of what is available online (I just ordered the book on Amazon) and I have a few questions related to starting the GW Diesel engine...

1. They bring the U-Boat up to 25 meters and raise the schnorchel, then continue up to attack periscope depth.
2. The schnorchel head is above the water and then the Schnorchel air supply shut-off valve is opened and the water in the schnorchel air supply tube is drained into the bilge.
3. The internal exhaust valve is opened to enable schnorchelling and the blowing valve for the selected diesel engine is opened to direct the exhaust gases to the schnorchel.
4. The GW Diesel engine is started with air...

Now, here is where your expertise is needed:
When the GW diesel engine is running on air, how long is it before you switch over to running on fuel oil? I believe the internal air pressure in the GW diesel exhaust system will start to build up at a fairly rapid pace. Therefore, they need to monitor the exhaust air pressure, and open the schnorchel exhaust shot-off valve at the appropriate pressure to blow out the water in the schnorchel exhaust side (something like blowing the ballast tanks). I doubt if the schnorchel exhaust blowing is done while the GW diesel engine is running on fuel oil...

Q1 - How long will the GW air startup normally take?
Q2 - The book stated that the GW supercharger and the MAN turbocharger must both be turned off while schnorchelling. I thought the MAN turbo charger was constantly running?

Regards,
Don_

Hi Don
The switching over to fuel was a matter of experience, the starting procedure at snorting was pretty much like starting the engines for residue blowing the ballastanks while surfacing, clearing the cylinders by blowing starting air and possible water out via the opened indicatorcocks, then shutting the cocks and admitting starting air to the cylinders and when the engine revs turned dead slow you added fuel according to your experience, as the system derived from the reversible engine design this was a fairly rapid operation, a matter of seconds rather than minutes. A starting failure was not a big deal, you simply repeated the start. As far as I remember if the exhaust backpressure exceeded 0,8 kg/cm2 the reliefvalve at the engine exhaustmanifold lifted and filled the engineroom with black smoke which could be cleared quickly if one engine was running.
The MAN supercharging system was indeed  driven by the exhaustgases and not by the camshaftdrive and clutch with interlock as on the GW engines. On the GW engines you could only clutch in the Roots blower at higher loads.
You monitored the exhaustbackpressure constantly as you did not want the relief valve on the exhaustmanifold to open. 
Tore

[Don Prince]

Hello Mr. Tore,

Thanks for the info...

According to Aaron's book:
1. They bring the U-Boat up to 25 meters and at a very slow underwater speed, they raise the schnorchel mast/lock and then proceed to where the schnorchel head is above the water and the exhaust pipe is below the water surface.
2. They drain the schnorchel air mast into the bilge, so the front tube ready for operation.

Now, the issue is how do they blow the water out of the exhaust pipe and start the Diesel engine at the same time? The schnorchel exhaust system will be flooded back to the schnorchel exhaust shut-off valve above the deck on the starboard side of the tower. So, the schnorchel exhaust pipe is flooded.

Question - Can you blow compressed air into the exhaust system while opening the schnorchel exhaust shut-off valve, and start the diesel engine during or very shortly after the blowing process. You do not want to open the exhaust relief valve with back pressure during start-up?

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

From Aaron...
"To the best of my understanding, based on the engineering reports and archival documents, the exhaust line remained, generally full of water. To what extent I do not know. The backpressure generated by the diesel engines kept the water at bay as the exhaust gasses were expelled. This is why it was so very important to close the shutoff valve at the end of snorkeling otherwise the water flushed back to the engines, forced toxic gasses into the engine room and could flood the engines."

Some of that doesn't make sense... If you stopped the diesel engine and failed to shut the schnorchel exhaust shut-off valve, then you could flood the engine. However, I don't see the toxic gasses into the engine room under that scenario.

Starting the Diesel engine for schnorchelling:

I imagine that you keep shut the external diesel exhaust valve, drain and open the internal diesel exhaust valve, and open the main exhaust valve (port or starboard) for blowing. Now, we have air filled pipes up to the schnorchel shut-off valve. At this point, you are setup for blowing the schnorchel exhaust mast that is full of water (about 8 meters high).

If we start the Diesel engine on air and monitor the exhaust pressure gauge for blowing the ballast. When the pressure gets to .5 kg/cm2, we open the schnorchel exhaust shut-off valve and switch the diesel engine to fuel (Start). Then bring the engine up to speed while clearing the schnorchel exhaust mast of water. Hopefully, when the hot exhaust gases hits the compressed air and it expands in the exhaust pipe system, it push the water up and out of the schnorchel mast exhaust pipe, and not cause exhaust safety valve in the diesel room to open...

Does this sound reasonable?

Regards,
Don_

[tore]

Don. There are many alternatives when omitting to do obvious things  as well as doing wrong things. The snorting system introduced at the end of the war was designed making use of the existing systems. Hence the snort/exhaust system was connected as much as possible to the exsisting system e.g. by a valveconnection to the drain chambers between each main/internal exhaustvalves. This means that the snort exhaust pipe could be drained by the original exhaust system drainage down into the bilge and pumped overboard. This would of course not imply filling the engineroom with black smoke (exhaust.) The main reason for getting exhaustleakage into the engine room with exhaustpressure exceeding the preset relief valve adjustment (mainly 0,8 kg/cm2) on the exhaustreciever. In rough weather you could of course dip the top exhaust outlet that much causing the reliefvalve to open( happened to me a couple of times).     I rather would drain the system the normal way if time allowed.
Tore

[Don Prince]

Hello Mr. Tore,

Did you raise and lock the schnorchel mast while on the surface, and then dive to schnorcheling depth?

Or -

Like Aaron discussed; They brought the U-Boat up to 25 meters depth and raised and locked the schnorchel mast, and then went up to schnorchelling depth:

1. The schnorchel head was above the surface, but the mast was filled with water. So, they drained this water into the bilge (problem solved), and now the schnorchel mast air intake section is cleared.

2. The exhaust pipe on the schnorchel mast is below the surface. So, they can not just drain the exhaust pipe because it would continue flooding with sea water (problem)? Somehow, they had to blow the water from the schnorchel exhaust section of the mast ahead of the schnorchel exhaust shut-off valve...

Under Aaron's scenario, how did you start the diesel engine and blow the schnorchel mast exhaust pipe clear of water?

Regards,
Don_

[tore]

Don.
 I really don`t remember raising the snortmast at 25meters nor to have seen  any indication in the german orderbooks mentioning such a maneuvre. We frequently raised the mast surfaced for service with no trouble.
Point 2. in your question draining the exhaust mast.  The exhaustpipe of the snortmast is connected via a shutoff footvalve to the exhaust blowingsystem and utilizes the two exhaust pipebranches ( port and stb) for residue blowing from the chamber between the outer and inner main exhaustvalves. This complicated watercooled valve casing is described in your Skizzenbook. As mentioned,  the chamber is enclosed by two valvedisks and hard to get watertight due to carbon formation on the valvesatings,hence a rotating valvdisc is provided, further the outer main exhaustvalve  is a flapvalve used for backpressure adjustments during residueblowing of the main ballast tanks. When the snortexhaust pipes are connected to this system it is connected to a fairly large internal drainage system operated by the large main drain pump in the controlroom. As we have discussed before, a massive intrusion of water in this system can be gravitydrained from the exhaust valvecasing chamber into the engineroom bilge before getting to the exhaustmanifold of the main engine, even this manifold has a substantial drainage capacity to the bilge before the water might enter the cylinders of the engines. Finally, getting water into the engines is not a disaster as we have discussed previously. Allowing water in and out of the submarine was a routine. Large and long half filled vessels could create a non desireable surface effect.


Tore

[Don Prince]

Hello Mr. Tore,


If there was an exhaust leak and some of the water backed up into the exhaust Manifold, then where is the valve located on the GW Diesel engine to drain the water? Is that drain valve located on Plate 15?


Regards,
Don_

[tore]

Don.
I don`t think the drainvalve is located on plate 15 as that is the starting air supplysystem. I don`t remember but guess it could be one of the valves indicated on plate 13 may be one of the valves having a sightglass. As mentioned the snortsystem were installed by the German navy latter part of WW2, at that time they were short of everything and the snorting system was designed pretty simple utilizing exsisting systems as much as possible hence existing airducts and exhaustblowing system were used. The exhaust system utilizes the exhaust blowing system going from the chamber between the outer main exhaust flapvalve and the inner main exhaust flapvalve continuing by the two pipes (stb and port) to the exhaust ballast tank blowing panel eg. 8 valves outside the pressurehull. The valves have elongated valvestems down into the controlroom. After this valvechest  the pipe continues passes a shut off footvalve operated from the controlroom and up the snortmast having outlet well below the ringfloat air intake valve.
You don`t clear the water in the snortmast exhaust system by blowing HP air but drain the mast by one of the drainvalves in the aft engine room, I don`t remember which but possibly the pipe with valve and sight glass.
Tore

[Don Prince]

Hello Mr. Tore,

I believe that valve (n) is used to drain the exhaust manifold of flooded seawater into the bilge, and the safety valve is to the right of it on Plate 15.

I had a wrong label on the large funnel and corrected it as "Drain into Bilge."

What do you think?

Regards,
Don_

[tore]

Don.
Checking the other plates 13 I figured out the plate 13 for the GW engines have wrong letters for several valves like valve p becomes o hence a wrong and confusing  naming and purpose of the various valves in the system.Below is a correction which might clear up the matter.


Tore