Author Topic: Tores mailbox VIIC and VIIC/41 operation and technical details  (Read 572866 times)

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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3660 on: 05 May , 2017, 13:53 »
Don.
I have checked the pages in Your Skizzenbuch as requested and have following remarks.
Page 72.....Reason-to maintan the u boats correct buoyancy..... With such small amount of fueltransfer mentioned there is hardly any changes in the submarines buoyancy,or, the difference in weight between fuel and seawater is roughly 0.15 kg pr. kg water and if you only top up the day tank of say 175 kgs this means some 25-30 kgs weight difference. Apart from pressurerizing the internal fueltanks, one of the main advantages of the compensating water is to reduce the surface effect of a partly filled tank by keeping the tank full all the time.

Page 85..... normally it is the engineroom staff checking the compensatingwater when fuelling, not the depot personell.

Page 97-99  I Guess we should need a bit more Research on the Junker exhaustsystem as it is currently too many loose ends.

Page 108-109  I believe you have to vent the buoyancy tanks at any diving as otherwise shall introduce fairly large tanks with considerable variable buoyancy and free surface effect. I assume replacing the venthandle ( Wheel) from fore torpedoroom to the controlroom was a consequence of the alleys air superiority in 1943, increasing the need for crashdiving and a quick control of the bow down diving in the controlroom.
The Atlantic bow was introduced as you say in 1943 to improve the surface condition of the submarine by reducing the longitudenal pitching. I don`t think the wider beam bow is describing the Atlantic bow, rather a flare bow.

I guess the buoyancy tanks might influence the submerged condition if not vented. The air volume of the bow boyancy tank at 50 meter is compressed from appr. 8m3 at the surface to 1,33 m3. Which means theoretically a loss of 6,67 m3 displacement at the bow and 3,567 m3 at the stern. A total displacement loss of 10.237 which has to be compensated. Generally you want to avoid large displacement variations by having easy compressible gases (air) taking part in the descend. In this case of not venting the buoyancy tanks you would have to compensate for the loss of displacement by pumping out some 10.000 liters regulating waters whereas to compensate for the total pressurehull compression you need only 500 liters. Of course the temperature influence the calculation, but assuming the cooling effect of the lower temperatures at 50 meters would compensate for the compression temperatures. At 50 meters the compression of the airdisplacement in the bow and stern buoyancy tanks would upset the buoyancy and the trim of the submarine as well as introducing an undisireable surface effect.

Page 125-126. The aux coolingwater pump.... is located on the fore bulkhead port side... stb side.

Page 143 Using the other engines lubeoil pump is possible, but not the first choice. It is far easier and quicker to use the electrically driven aux. lubeoilpump by that you are able to use both systemtanks.

Page 144-145 As discussed earlier, the easiest way to transfer fuel from the submarines fueltanks is by submitting compensating water under pressure to the tanks. The aux.fuel tranfer pump is primarily used for draw fuel from another source (submarine?) to the fuel storage tanks.
Luboil hand pump. Normally the electric driven aux. pump was running before starting or turning the engines. The luboil handpump was as you say mainly used for maintenance jobs as well as for topping up the systemoil by fresh oil from the storagetanks.
Page 148. In the event of a failed luboilpump my first choice would be to use the electrically driven aux.lubeoil pump in stead of hooking up to the other engines luboil pump.
Page 429 Transfering fuel from inboard tanks to saddletanks. I am not familiar with not using the internal fueltanks and not cracking the while schnorcheling and not cracking the compensating water board valve. The reasoning that the engineroom gravety tank ( daytank) might be based on a misunderstanding as this tank is an open tank with 6 overflow pipes. May be you are refering to the interanal storagetanks?
The transfering of fuel from the inboard tanks to the saddletanks is a bit complicated to me as by pumping out fuel without watercompensating you introduce a fairly heavy surface effect in the large fueloil storage tanks during schnorcheling which you absolutely do not want. If you neverteheless should choose to pump fuel from th inboard fuel tank to the saddle tank you could just as well pump it to the gravety tank in the engine room.
« Last Edit: 05 May , 2017, 13:59 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3661 on: 05 May , 2017, 22:23 »
Hello Mr. Tore,


Thank you for reviewing the many pages...


Page 72 - I was attempting to get across that compensating water always had to replace the fuel oil forced into the day tank.  Eventually, the internal tank would be half empty; in other words half fuel oil and half compensation water.  Possibly the U-Boat would not be able to dive if the internal tanks were half fuel oil and no compensating water.  Was my attempt too awkward?


Page 85 - I changed form "depot personnel" to "engine room personnel" in two places on that page...


Pages 97-99 - I agree...


Pages 108-109 - I changed the word "wide beam bow" to "flared bow"


Type VII C/41
surfaced displaces 759 tons
submerged displaces 865 tons
increased displacement when submerged 106 tons


This is the displacement (106 tons) from anything above the water line; pressure hull, tower/bridge, deck and casing, cannon, etc. I don't believe there is any weight gain by flooding the ballast tanks, just a loss in buoyancy because of venting the air volume in the ballast tanks.


Therefore, when the U-Boat dives and doesn't vent the buoyancy tanks, the air is compressed with depth to a greater extent and has little effect on buoyancy the deeper the U-Boat dives, but the water displacement gain in the buoyancy tanks does not need to be compensated for by pumping water from R1 or R2.


Where have I gone wrong again? I don't believe we need to counter the water weight in the flooded ballast tanks...


Pages 125 - 126 That was a dumb error, I had it correct on the drawing...


Page 143 - I added another line to the page with your sentence...


Page 148 - I think page 143 may be sufficient... What do you think?


Page 429 was taken from a U-Boat KBT from the uboararchive.net web site...

Note - the attached drawing seems to indicate there was the ability to hand pump the dirty oil tank contents overboard into the sea.  The current U-995 only has that short pipe with an end cap. That looks modified or wrong to me?

Kind regards,
Don_
« Last Edit: 05 May , 2017, 22:26 by Don Prince »
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3662 on: 06 May , 2017, 08:01 »
Don.
The displaced water of a surfaced submarine is equal to the total weight of the submarine including equipment and crew. This displacement creates a positive buoyancy which makes the submarine float at required draft adjusted by the regulating tanks.
As a submerged submarine displaces the superstructure with pressurecontainers, ducts etc., above the surface waterline in addition to the surface weight deplacement, the submerged displacement of a submarine is larger than the surface displacement. This submerged displacement consist of components with variable compressabilities of which the gases (air) has the highest and steel the lowest. For a VIIC the pressurehull compression would be about 100liter per. 10 m, steel and other solid practical nil and possible air in tanks connected to the sea according to Boyle Mariottes Law: P1V1/T1=P2V2/T2.
As the submarines ballast tanks are vented, the displacement air is substituted by seawater and the displacement caused by the air is removed. The buoyancy created by this displacement is gone causing he submarine to have a passive descent if the regulating tanks are adjusted to a weight slightly larger than that of the deplacement loss.
During the descent the ambient waterpressure increases and a  compression of the compressable components start. As a consequence the submerged displacement decreases. This has to be compensated by discharging an equal amount of regulatingwater .
The pressurehull compression at 50m depth has to be compensated by 50 l.and a possible non vented bow buoyancytank of 8m3 would get an air compression to some 1.33m3 which means 6,67m3 less than the sealevel volume, thus the displacement of that tank would result in a buoyancy loss of 6,76m3 which has to be compensated to maintain the required buoyancy at a given depth. The easiest way to avoid such correction would be to vent the bow and stern buoyancytanks when diving and let the tank act as a freeflood area.
Tore
« Last Edit: 06 May , 2017, 08:06 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3663 on: 06 May , 2017, 20:03 »
Hello Mr. Tore,


Thank you for the info about displacement when diving the type VII U-Boat...


"possible non vented bow buoyancy tank of 8m3 would get an air compression to some 1.33m3 which means 6,67m3 less than the sea level volume, thus the displacement of that tank would result in a buoyancy loss of 6,76m3 which has to be compensated to maintain the required buoyancy at a given depth."


The bow and aft buoyancy tanks are above or at the waterline when the U-Boat is running on the surface... Therefore, the weight of these empty tanks (except for air) is compensated for at the U-Boat's waterline.  In a non-emergency dive the non-vented buoyancy tanks only present an air pocket which will slightly inhibit the U-Boat's diving rate, but as depth increases the air pocket is compresses and the overall diving resistance becomes nil at greater depths.


I don't see a buoyancy loss where any compensation is required in this scenario for the buoyancy tanks...


In an emergency dive the buoyancy tanks may be vented to eliminate the air pocket resisting the diving rate.


I apologize for my constant doubts, but I would like to fully understand this diving process.


Regards,
Don_


PS - This post of mine is numbered 666 - I guess the Devil is in the details... Ha ha!
« Last Edit: 06 May , 2017, 20:07 by Don Prince »
A man's got to know his limitations...
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3664 on: 06 May , 2017, 23:44 »


Don.
I guess we  talk about Archimedes in this case and variable displacements and buoyancy: a body immersed in a fluid partly or wholly is boyed up by a force equal the weight of the fluid displaced by the body.  Just below the surface the volume of a not vented bow buoyancy tank displaces 8m3,  hence the submarine is buoyed up by a force equal to the weight of 8m3 seawater. As the air trapped in the tank is substantially compressed at 50 m depth to some 1.33 m3, the buoyancy force is still equal to the weight of the displaced seawater, however the displaced sea water, practically not compressible, is now decreased to 6.67m3 hence the buoyancyforce of the tank is 8-1,33= 6.67m3 less. The same happens to the pressurehull which is far less compressible than the trapped air in the buoyancy tanks. You can`t use Boyle Mariottes Law on the pressurehull, but an experience figure says the pressurehull is compressed by 100 l. per 10 meter diving depth corresponding to 500 l at 50m depth. As for the increased displacement due to the superstructure, the displacement changes are practically nil because it is not compressible as long as you don`t have airpocket trapped somewhere.
The basic for a submarines passive changing of diving depth  is changing the buoyancy force, diving by reducing the displacement (buoyancyforce) by venting the ballast tanks and surfacing by increasing the  displacement(buoyancy force) emptying the ballasttanks.  The buoyancy tanks are not listed as ballast tanks and do not participate in such diving procedure thus should be vented at the surface prior to diving and considered as a  freeflood area when submerged. to overcome the surface "resistance" you should use the Q tanks (Untertriebzelles).

Tore
« Last Edit: 07 May , 2017, 08:53 by tore »

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3665 on: 07 May , 2017, 01:37 »
Being practically fully installed in my summerfarm, I have been able to pickup my painting hobby and brushed up my old painting of KNM Kaura ex U 995 on an immaginary crossing of the westfiord in Northern Norway around 1953. The old steamer in the background is the "expressship" S/s Finmarken southward bound wheraes the KNM Kaura is going north to the Barentz sea.
Tore

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3666 on: 07 May , 2017, 20:23 »
Hello Mr. Tore,



"Just below the surface the volume of a not vented bow buoyancy tank displaces 8m3,  hence the submarine is buoyed up by a force equal to the weight of 8m3 seawater."


Yes! I understand that statement...


"As the air trapped in the tank is substantially compressed at 50 m depth to some 1.33 m3, the buoyancy force is still equal to the weight of the displaced seawater, however the displaced sea water, practically not compressible, is now decreased to 6.67m3 hence the buoyancy force of the tank is 8-1,33= 6.67m3 less."


The 2nd sentence seems to emphasis the negative...
So the U-Boat at 50 m is buoyed up by the force equal to the weight of 1.33 m3 seawater (The effective buoyance displacement was reduced with depth). The 8m3 bow buoyancy tank was never part of the displacement balancing equation (Not Part of the Ballast System). When the U-Boat is on the surface; there is no positive buoyancy created by the bow buoyancy tank because it is above the waterline. Hence no compensation was required especially for air...


I think we both agree with that statement (Yes/No)?


The weight of the U-Boat prior to the dive is the same at 50 meters, or at 200 meters... However, the displacement (Volume) may be less because of hull compression and some water may be pumped from the regulation tanks to compensate and balance the U-Boat.


THE BOTTOM LINE____


I could see the U-Boat taking in 1,330 liters of water at a depth of 50 meters to compensate for the air contents in the bow buoyancy tank. However, if the U-Boat went down to 200 meters depth, the they would need to pump out about 1,000 liters of water to balance. That would not be desirable in an emergency situation and required to use the batteries to pump out the excess weight.


From our previous discussions, the buoyancy tanks were not considered as part of the ballast system. Mr. Tore - do you know if your Karua crewmen utilized the buoyancy tanks during a dive? I would think (Given with my lack of expertise) that the buoyancy tanks were only vented during an emergency dive situation...


What do you think?


************ Your Latest painting *******************


Excellent work, the airbrushing really makes thing pop out from the canvas.  My wife's (Maureen) father (Johannes) took painting lessons after he retired and did water color paintings before they moved to the US. He passed away about 3 years ago at the age of 89, her mom just turned 90 and is in good health. Did you take any painting lessons? Again Excellent work my friend!!!


Do you mind if I just use your latest painting in Skizzenbuch?


Kind regards,
Don_
A man's got to know his limitations...
Harry Callahan, SFPD

Offline SG

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3667 on: 07 May , 2017, 21:58 »
Tore, the painting is great. Waves and sea are masterfully rendered. Congrats!

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3668 on: 08 May , 2017, 11:58 »

Don.
I guess a graphic could explain my ideas better that the poor wording, see below. I think we are in agreement with your first paragraph.

The weight of the submarine prior to the dive is the same at 50m or at 200m. I agree if you dont`t pump out any liquid or discard any objects from the submarine.
However the volume, displacement may be less because of hullcompression and some water may be pumped out of the regulating tanks to compensate. The water pumped out of the regulating tanks has no influence upon the volume/displacement but on the weight of the submarine, however if you blow out some water from the buoyancytanks it shall increase the submarines volume and thus the buoyancy of the submarine.
I could see the Uboat taking in 1.330 liters at a depth of 50 meters to compensate.
I assume you are referring to buoyancy tanks not vented. I guess you are missing a 0 here as at 50 m you have a total loss of buoyancy of 12,22m3- 1,33m3= 10,89m3  pluss the pressurehull compression 0,5m3 alltogether 11,39m3 water equal to 11.390 liters, a considerable amount of water to be pumped out against 50m.
At 200m the total regulating water which is required to be pumped out of the two regulating tanks would be some 15.200 liters to compensate for the aircompression in the buoyancy tanks if not vented. In case they are vented, nil. This is one of the main reason that the buoyancytanks should be vented prior to diving
The ballast tanks are normally not used for ballancing and trimcontrol. We use the regulatingtanks and the trimtanks as they are easier to control for such purposes. Again, a partly filled ballastank/ buoyancy tank create a fairly large free surface effect momentum. The regulating tanks are centrally placed and small length which minimize these unfavorable elements.
On the surface the buoyancy tanks have the vents shut, this is increasing the bow and stern buoyancy when the submarine is pitching, sometimes immersing the buoyancy tanks, hence together with the flared bow reducing the pitching which is the purpose for the tanks. At calm sea they have no function.


Re Graphic below.
If you don`t vent the buoyancy tanks submerged, the light blue area e.g. displacement becomes smaller as the seawater intrusion (dark blue) get larger( representing loss of buoyancy). A VIIC having a displacement variation between 6 and 11m3 not compensated would get trouble with the dynamic control of the submarine. Thus you have to compensate this decrease in buoyancy force by reducing the submarines weight, this is normally done by discharging regulatingwater by less extreme volumes..
On Kaura we kept normally the buoyancy tankvents shut at the surface and open as a routine in the divingpreparation.
In the event of a crash dive all the tankvents were opened including the Qs starting with the bow tanks.
 Both Q tanks corresponds to a buoyancy of 4m3. If the buoyancy tankvents were shut they would represent a buoyancy force of 12,22 -4= 8,22m3 displacement, a hopeless figure for crashdiving and destroying the normal exellent short divingtime of 30 seconds for a VIIC.
the buoyancy tanks were not only vented in emergency cases, but always when diving .
Tore
« Last Edit: 08 May , 2017, 12:05 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3669 on: 08 May , 2017, 16:14 »
Hello Mr. Tore,


I searched through the entire "German Diving Regulation Manual," and not once are the Aft or Bow Buoyancy tanks discussed. However, they do cover the Negative Buoyancy Tank...


Regards,
Don_
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Harry Callahan, SFPD

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3670 on: 09 May , 2017, 01:28 »

Don.
The Germans did not use the wording tank or buoyancy for these tanks, they simply called it for what is was, watertight bow and watertight stern. Wasserdichte  bug and heck.
In the hand book for the uboatcommander you shall find the watertight bow and stern mentioned as per my enclosure. The English translation is a bit wierd trying to make german words english, but anyhow I guess it would explain that the germans did as we, leaving the buoyancy tank vents open submerged.
By the way I forgot to answer you question on my recent painting, of course you are free to used it in your Skizzenbuch. Allthough I am as old as your father in law was, going on 89, I never took any painting lessons.
Tore
« Last Edit: 09 May , 2017, 02:24 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3671 on: 09 May , 2017, 14:05 »
Hello Mr. Tore,


OK... So, If I understand the functionality of the bow ans stern buoyancy tanks, then the following statements are true.


1. Technically the bow and stern buoyancy tanks are not part of the ballast system because they are normally above the waterline and not affecting the U-Boat's overall displacement.


2. The bow buoyancy tank's primary function is to counter under cutting.


3. The stern buoyancy tank's primary functions are to assure the bow is in a down angle during a dive, and it's above the waterline for the Junker's air compressor operation.


4. Both the bow and stern buoyancy tanks are vented after a dive is initiated to eliminate the air pocket which will impact the decent rate slightly.


Comments?


Regards,
Don_
A man's got to know his limitations...
Harry Callahan, SFPD

Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3672 on: 10 May , 2017, 01:13 »
Don.
Buoyancy tanks. In reply to your last post.
1. Yes, in bad weather surfaced having vents shut they increase the bow displacement when pitching, submerged vented, they are neutral as any non compressible material.
2. Yes, and reduce pitching movements.
3 No, the primary function of the aft buoyancy tank is to reduce pitching and increase displacement( buoyancy) , surfaced in bad weather, to counter act flooding of the Junker exhaust pipe.
The bow down angle assistance at passive diving is executed by main ballast tank 1 which is vented a bit later than the other main ballast tanks. The total bow down angle is achieved by speed and hydroplanes, dynamic, and the main ballast tanks ,passive. Both buoyancy tanks do not participate as they are vented prior to the diving order.
4. Normally both buoyancy tanks do not have any airpockets submerged as they are vented. The vents are shut after they are drained on the surface. If the weather  is bad you might speed up the surface drainage by shutting the vents and blow the tanks by LP air.
Tore
« Last Edit: 10 May , 2017, 01:22 by tore »

Offline Don Prince

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3673 on: 10 May , 2017, 14:49 »
Hello Mr. Tore,
Hello Mr. Tore

I believe I read somewhere that the Junkers air compressor could be operational up to Sea State 5 - Wave height 2.5 to 4 meters, and swells moderate/long. I don't know if sea state 5 was the cut-off limit or was included in the operational zone?

Diesel Engine Starting

The second thing that became apparent to me was when you are starting either the GW or the MAN diesel engine with compressed air. According to the Diving Reg. Manual, the tail clutch should be dis-engaged and the clutch engaged between the diesel engine and the e-motor, so the e-motor can acts as a flywheel... Is this always the case when starting the diesel engine?

When running on starting air, at what rpm was fuel injected?
At what RPM do you engage the tail clutch to the prop?

How is the change over done when diving the U-Boat?

1. Do you shutdown the diesel, disengage the clutch between the diesel engine and the e-motor (both not running) and then start the e-motor to drive the prop?

OR -

2. Do you start the e-motor, then dis-engage the clutch (both running) to the diesel engine and then shutdown the diesel engine?

Conclusion - It looks like option #2 could be done in parallel with both diesel engines. While option #1 needs to be done serially because you don't want a sudden drop is speed.

When surfacing from a dive, what would be the diesel engine starting procedure?

3. Would you stop one e-motor, engage the Deisel/e-motor clutch and dis-engage the tail clutch to start the diesel engine, and then engage the tail clutch?

OR -

4. How???

Regards,
Don_
« Last Edit: 11 May , 2017, 00:10 by Don Prince »
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Offline tore

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Re: Tores mailbox VIIC and VIIC/41 operation and technical details
« Reply #3674 on: 10 May , 2017, 23:25 »
Don.
I don`t believe you can put up accurately a sea state where you could not operate the Junker, it all depends on different circumstances like the trim, how you place the submarine in relation to the waves, the speed and course of the submarine etc.
The main engines were started both with the mainclutch engaged or disengaged as well as  with propeller engaged and disengaged. Of course when you were charging the batteries alongside  at the quay, you disconnected the propeller clutch. Before they removed the reversing of the diesels, the engines were started and stopped many times during maneuvring ahead and astern with propeller engaged.
The injection of the fuel during start was a matter of the engineers feeling and experience. I should think some 30-50 revs. depending how much massforces were engaged on the propellershaft.
You engaged the clutches preferably at stop, otherwise at the lowest possible revs. Again, it was depending on the massforces connected on the shaft. The higher the speed and massforces, the more wear and tear on the double cone clutches. If you engaged the mainclutch even at moderate revs, the friction forces created smoke from the friction layors.
Tore
« Last Edit: 11 May , 2017, 02:06 by tore »