Tores mailbox VIIC and VIIC/41 operation and technical details

[tore]

Maciek-Mark.
You are much better with organising the paperwork Maciek, thanks. We use the word Peilung  Norwegian peiling just in the same way as the Germans. When it comes to larger amount like KM3 and oceandepth we use the word, sounding, like echolot sounding.
Some time ago I got a board, I guess from Maciek, showing the relation between rpm and speed for a VIIC together with the previous figures it might be of some help for checking the output, rpm, bmep and speed relations graph.
Tore

[VIC20]

I think the HP is possibly too low - But I've used the data from Maciek's picture:


http://models.rokket.biz/index.php?action=dlattach;topic=921.0;attach=5034;image


and when the line get's interpolated it just has so little HP at 180 RPM - the lowest data I've used from Maciek's picture is 158 HP at 256 RPM







Anyway the RPM of the propeller is what's used to calculate the trust so it does not affect the speed of the boat in my simulation.
The only effect it has is (if the resulting HP is wrong) is the time how long it takes to spin up to those RPMs.


I've just found out that the torque on his document does not fit to the other data of the RPM and HP:


3456 Nm at 180 RPM should be 118.44 HP which makes much more sense
6810 Nm at 256 RPM should be 244.84 HP instead of 158


at 390 and 470 RPM both curves give pretty similar results


So my guess is the RPM/HP data on the document is not correct.

[tore]

Mark.
I see, however when you are running the engine at very low outputs I guess the graph would be unreliable as the heatlosses of the engine becomes an increasingly and very large  proportion of the  bhp so I guess you can`t just interpollate the graph  down to 0 output. ( at 0 bhp you would would require a certain indicated hp just overcome the mechanical and thermodynamical losses to get the engine idling).
Tore

[VIC20]

Low RPM are not that important for me anyway.
But for the 180 RPM (which I need for KF) the HP or the MEP must be wrong on Maciek's data.


When looking at the data of the Type IX from this page 10 of this website: http://www.uboatarchive.net/DesignStudiesTypeIXC.htm


490 RPM - 2470 HP
480 RPM - 2320 HP
470 RPM - 2170 HP
426 RPM - 1630 HP
383 RPM - 1080 HP
295 RPM - 542 HP
218 RPM - 217 HP


Recalculation this with propeller law is pretty close:



490 RPM - 2458 HP
480 RPM - 2311 HP
470 RPM - 2170 HP
426 RPM - 1593 HP
383 RPM - 1174 HP
295 RPM - 536 HP
218 RPM - 216 HP


So when I do the same with the Type VII engine based on (uncharged) roughly 341 RPM (511 HP) from Maciek's data I will get


KF 180 RPM = 75 HP
LF 275 RPM = 268 HP
HF 340 RPM = 506 HP


now based on 470 RPM and 1400 HP:
GF 435 RPM = 1109 HP
AK 470 RPM = 1400 HP
480 RPM =1491 HP
490 RPM =1586 HP


So the calculation based on the propeller law for KF 180 RPM 75 HP is somewhere in the low middle of what the RPM-HP and MEP-HP data shows (50 HP and 118 HP).
The lowest data I've used is already wrong (158 HP at 256 RPM - it should be more like 216 HP for 158 RPM)
I guess the best is to "fix" the low RPM data with data calculated with propeller law and to stop thinking about it ;-)
 

[tore]

Mark.
This sounds like a better solution and bmep would be adjusted to more familiar values.
Tore

[VIC20]

Tore, I need a way to convert diesel fuel (in kg) to liters. But I have no idea about the diesel fuel used by the Type VII during war. Do you have a rough estimate?

[SnakeDoc]

Hi Mark,

Tore, I need a way to convert diesel fuel (in kg) to liters. But I have no idea about the diesel fuel used by the Type VII during war. Do you have a rough estimate?

Have you seen this: http://www.fischer-tropsch.org/primary_documents/gvt_reports/USNAVY/usn_187_45.htm


--
Regards
Maciek

[tore]

Mark
I believe the German WW2 Navy had a special specification for the  submarine fuel. During WW2 most of the fuel in Germany would be synthetic fuel made from brown coal. There are several processes which are used. My guess would be for the navy a so called hydrogeneration process was used I, believe a common process is called Bergius process (Kohleflussigung.) I still remember the smell as it had a high degree of aromatic content.  A typical specific gravity of such fuel would be in the range 0.85-0.885. This is an assumption from my side.
Tore

[VIC20]

Thanks.


Do you know if there were different types of compass repeaters on the bridge? One source says the destroyed one on the picture would be a pressure proof U-Boat compass, but I never saw one like this one on pictures.

[SnakeDoc]

Do you know if there were different types of compass repeaters on the bridge? One source says the destroyed one on the picture would be a pressure proof U-Boat compass, but I never saw one like this one on pictures.

Check out this thread:
http://models.rokket.biz/index.php?topic=1088.0
I'm not sure if these repeaters are for helmsman or they are repeaters for bearing (navigational) purposes.


--
Regards
Maciek

[Don Prince]

hello Mr.Tore and All,


I believe I have a basic understand of how the Header/Buffer tank works... 


1.  Heated water is pumped from the diesel engines and through the pressure hull to cool the exhaust mufflers.  Then the heated water is directed to the buffer tank and is channeled to the RFO tanks, the overflow pipe (which looks to dumped into the sea).  I believe the goose neck pipe is to provide air equalization in the tank.


2.  I had a problem with the lack of a closed pressurized tank.  The amount of water pressure provided to the RFO tanks is the result of the height of the water column form the deck of the Winter Garden to the level of water in the tanks.  I guess it's really ingenious; as the tank's water level rises the water pressure becomes less (self regulating).


3.  When the U-Boat submerges, the external tanks are open to the sea through the buffer tank pipe and as professor Maciek point out to me awhile back; the internal and external pressure is the same with an open tank.  The internal tanks are protected by a closed hull valve and should not see the external pressure.


I do have a question about the buffer tank.  the 4th pipe to the right looks like an arrow pointing down.  What is this?


I will post a drawing...


as always any comments are highly appreciated...


Regards,
Don_

[Don Prince]

If the U-Boat is configured to use the RFO tanks and fully loaded with fuel, is there a sequence of which tanks are used first?  From Plate 9 it looks like fuel oil can be taken from any external or internal RFO tank.


Regards,
Don_

[tore]

Don.
Compensating water headertank.
I Guess you got it OK. The headertank in the towercasing is always topped up by the attached colingwater pumps when the main engines are running and the head never exceeds the head corresponding to the watercolumn from the bottom of the tanks to the top of the waterlevel in the headertank even being submerged as the footvalves in the saddle tanks are valves which can only be placed in two positions, either to the bottom of the tanks or to the sea. We discussed this detail some times ago and Simon made one of his marvellous drawings of the system see drawing below. As you see the downpointing arrow is a drain. The fuel can indeed be taken from any fueltank and I don`t remember we followed any strict sequence, but as usual there was a communication between the engineers and the officier responsible (in our navy No 1, in the German navy chief engineer) for the trimcalculation as to which tank would be most convenient.
Tore

[tore]

Mark.
Compass repeaters on the bridge.
Sorry I was not very much involved in the compasses and I cannot remember which type of compassrepeaters which were on the bridge. I guess Macieks link can give a clue if not, I am sure there are a lot of clever guys out there having done some research on the matter.
Tore

[VIC20]

Some changes. RPM now closer to what I wanted to set them. Added faked cavitation (was too complicated to do it right) - overall the acceleration is slower now. Please tell me how the acceleration (and final speed per RPM) looks for you now. 


http://www.hessburg.com/downloads/Engine3/Engine3.html