Tores mailbox VIIC and VIIC/41 operation and technical details

[Don Prince]

Hello Mr. Tore,

When the U-Boat is on the surface or schnorchelling...

The hull/sluice valves in the diesel room can provide cooling water for both diesel engines and cooling water to the e-room for the e-motor coolers, e-motor bearings, thrust bearings, e-compressor, and the junkers compressor (if present). The diesel engine's cooling water returns to the sea via the diesel exhaust muffler vents, the header tank, the exhaust muffler exit ports on the Junkers compressor (if present), and the open Starboard hull/sluice valve in the e-room.

When the U-boat is running submerged...

The Port hull/sluice valve is providing the cooling water to all said components in the e-room, and the sea water is returned to the sea via the open Starboard hull/sluice valve in the e-room. I believe this source for cooling water also feeds forward though the diesel engines and some may exit to the sea via the diesel mufflers and the header tank...

MY Question Is...

In all instances; running on the surface, schnorchelling, or submerged - The e-room Starboard hull/sluice valve is open and draining circulated cooling water to the sea.  What would be the reason for ever shutting this valve? It looks like components in the e-room require this valve to be open; including the thrust bearings???

Regards,
Don_

[tore]

Don.
The intake of seawater is usually controlled by opening and shutting of boardvalves. In general all valves beween the sea and the inner part of the pressurehull is controlled by a valve having a circular valvedisc . All the valvediscs of the seavalves are opened against the seapressure, hence the seapressure keeps the valvedisc shut on the seating. As this design usually involves friction and a capacitydrop, these valves are primarily used as seaintakevalves. The seawater system inside the pressurehull is usually fitted with ordinary valves with circular valvedisks as well. The exception is the large capacity crossover supply pipe which is fitted with freeflow gatevalves and the lesser distribution branches from the crossover with ordinary valves having valvediscs.


There are several cases you need to shut the seaboard valves.  In the event of a deep dive and depth charge attack the procedure of the order: "prepare for depthcharge attack or deepdive" involves shutting of the seaboard valves.
Hence as a rule you always want to have a double security on the boardvalves.


Tore

[Don Prince]

Hello Mr. Tore,

Do you have a drawing of a circular valve disc assembly?

From what data I see on the e-room cooling water pump, the stats are:
Centrifugal Type
250/385 liters/minute
12 atmospheres head pressure

If the U-boat goes to a depth of 150 meters... The pressure at the e-room Port and Starboard valve heads would be 14.51 atmospheres. Therefore, the CW Pump sees no restrictive head pressure (equal pressure at both sides input and exit), so the pump can normally function and supply CW to the internal needs of the U-boat.

However, I do believe there would be a pressure differential seen between the water lines internal pressure and the U-Boat's internal atmospheric pressure. In the movie Das Boot you saw water lines bursting and rivets popping when the U-Boat plunged below 200 meters...

I definitely see a need to close the valves during a depth charge attack because of the possible differential pressures depending upon the explosion location relative to the U-boat.

Are you aware of any reported damage to the CW Pump, CW intake valve, CW exit valve, due to a depth charge attack?

Other than the attached photo...

Regards,
Don_

[tore]

Don the capacity of a centrifugal pump is following the QH graph as the design of the impellor, hence a given certain capacity is always followed by the head. Below is a typical drawing of a seaboard valve (As I couldn`t find a proper engineroom board valve, it`s belonging to the torpedotube system) which I guess speaks for itself, followed by a drawing which shows the internal freeflow of a gate valve. The most common reaction to a high pressure in the internal system is blowing of flangepackings and stuffingboxes.

Tore

[Don Prince]

Hello Mr. Tore,


I have been looking closely at the e-room Port hull valve and it looks like the hull valve is bolted to a plate that is welded to the pressure hull. Also, the hull valve vent grill looks to be screwed to the welded plate as well. See the two images...


Regards,
Don_

[Don Prince]

Hello Mr. Tore,

When you dive the U-boat both diesel engines are stopped so the attached cooling water pump has stopped. However, I believe you still need to cool the diesel engine. Therefore, the cooling water pump in the e-room looks to be able to provide cooling water to both diesel engines if you opened valves e1 in the valve chest, or you could use the auxiliary cooling water pump in the diesel engine room?

1. On a dive did you normally shut both engine room hull cooling water intake valves and use the valve chest and open valves e1 to provide cooling water to the diesel engines and then shut valves e1 after the engine were cooled down?

2. I would think that you would not want to use the diesel room's auxiliary cooling water pump to cool the diesel engines during a dive because now the control for powering the U-Boat is in the e-room.

Second thought!

If the U-Boat goes very deep and is under a heavy depth charge attack... Could they close all hull valves and stop all water cooling to the e-room to protect the U-Boat from bursting pipe flanges, etc... Now they could run the e-motors at creep/crawl speed and hopefully not over heat the thrust bearings or the e-motor bearings. Do you know if this is a possibility?

Regards,
Don_

[tore]

Don,  normally it is up to the first engineer to decide the various components to operate as it all depends on many variable like maintenance, weather,mission etc. The various systems however are very flexible and allows many alternatives. Unfortunately some of the systemsketches are not correct as plate 13, showing the coolingwater system for the GW dieselengines. On the enclosed plate 13 I have corrected the crossover pipe allowing stb engine and the aux. coolingwaterpump to take suction  from the pipe. In general this pump will be used for the diesels instead of the E room coolingwater pump.


Tore

[tore]

Don, your last question: in emergency you do anything and I dont think at dead slow speed, major damages occur to thrustbearings, E-motor bearings etc. in case of seawater cooling is shut.
Tore

[Don Prince]

Hello Mr. Tore,

Yes I was aware of the connection on Plate 13... I have attached the Skizzenbuch modified drawing and I noted two (2) locations with a RED circle on the print.

It's good to know that the diesel room auxiliary CW Pump was used to continue cooling the Diesel engines. Do you remember how long that process would last? I would not believe it took too long...

Regards,
Don_

[Don Prince]

Hello Mr. Tore,

I have attached below a photo of the various diesel exhaust arrestor on Kaura (ex U-995) and others:

1. If the exhaust exits the spark arrestor above the water line is there a staring black smoke?
2. If the exhaust exits the spark arrestor below the water line is there a starting white smoke?
3. Was there ever a time when actual sparks were seen exiting the above the water line spark arrestor?

Regards,
Don_

[tore]

Don. The exhaust is usually an indicator for the condition of the engines like fuel nozzles and coolingwater leakages. Normally you would not notice any black or white exhaust. A bad fuelnozzle or overload would create a black exhaust and white smoke a coolingwater leakage like corrosion holes in the exhaustvalvecage. Nevertheless the exhaust would leave some deposits of black carbon at the exhaust outlets  and you migth see some of the VIIC casings  have been painted black just above the outlet to disguise the deposits. You very seldom see any sparks at the exhaust outlets.

Tore

[Don Prince]

Hello Mr. Tore,


Can You look at the attached image and answer the question between Simon and I???


Regards,
Don_


PS... Sometimes it may be a good idea to read my own book...



Exhaust Port and the Spark Arrestor


The VII Cs had a number of different exhaust outlets and possibly spark arrestors. The colleague of photos to the left shows 5 versions. The spark arrestors for U-Boats may be of two executions; wet or dry. The dry spark arrestor has an intricate system of baffle plates to arrest the sparks inside a casing. In the wet execution, the engine cooling water is sprayed into the arrestor or the gases are emitted into the water cooling well. In both instances they are placed above the water surface (sea). Another version is when the exhaust is emitted below the water surface (sea) without any special casing for a spark arrestor. The latter execution was the original U-995 design [Top right photo (RED circle) KNM Kaura/U-995 in dry dock in 1953]. This was changed on todays museum U995 as shown on the top left photo; the RED circled area indicates the Bold ejection port just aft of the rebuilt exhaust outlet location.

[NZSnowman]

Hi Tore & Don

A few questions about the Spark Arrestor and if it utilized cooling water.

* In the Design and Specification Books, Volume M on plate 13B, it shows no cooling water going pass the end of the diesel exhaust silencer.
* If it did spray cooling water into the Spark Arrestor, how was the amount of cooling water control?
* If cooling water was sprayed, this would lead to negative pressure in the cooling water system, does this mean they had to constantly add sea water to the system to replace the lose cooling water?

[tore]

Don and Simon.
As Don says there are a number of executions to the exhaust outlets in the casing,  the execution I guess, might depend on the on the mission for the relevant boat. As on Dons image, the sparkarrestor is clearly visible adjacent to the silencer. Water spraying in the sparkarrestor is mainly a design for motorlaunches and I cannot remember it is used for the VIICs, a better solution would possibly be to end the exhaust pipe below the watersurface. The exhaust system is cooled by the main coolingwater system which leaves the pressurehull via the mantel of the main hullexhaustvalve  with intricate passover the flanges up to and including the silencer. From the silencer the pipesystem end up in the fuelcompensating headertank in the towercasing having an overflow under the casingdeck to the sea, thus not visible. There are quite a few drain valves in the system allowing for draining the coolingwater mantels ( for artic operations). Below is an image showing the original exhaustoutlet in the casing as originally fitted on U 995 during the hand over October 2.  1971.

[Don Prince]

Hello Mr. Tore and Simon,

I do not believe we would ever see a negative water pressure in the cooling water system... Once the water compensation system is stabilized there is no further drain on the cooling water system because the diesel engines are drawing fuel from the day tank which is not water compensated. Therefore, the constant cooling water drainage is at the mufflers and at the header tank under the winter garden. Each engine mounted water piston pump can supply 48 cubic meters of CW per hour (the Electric Auxiliary CW centrifugal pump has the same capability). This definitely looks to be a pressurized cooling water system by design.

It looks like both U-995 and U-926 originally had the exhaust exit below the water line according to the shipyard and surface images. U-995 was converted to the exhaust exit above the water line during the museum refurbishment. This is one more item that they should have left as original!

Regards,
Don_