Sub keeps sinking!?

[JayDee]

Originally Posted by smg13

Why would I want to hover making noise? Uhm...maybe I am waiting in bad weather at periscope depth, for a convoy or a single ship to roll by...

In good weather, a very good LI was actually able to make the boat hover without making noise at periscope depth (with the periscope raised). If he got the neutral buoyancy "almost right" by +/- a few kg, when e.g. the boat slowly sank deeper, the periscope going down in the water would add to the displacement - to the point where the buoyancy is exactly neutral.

@Sailor Steve:

Underwater the sub needs to maintain a precise neutral bouyancy to not rise or sink, which requires a touch that only a modern computerized pumping system can maintain.

Not necessarily "modern" or "computerized", systems like that were developed during WWII by Friedrich Tuschka for a company called Askania (a kind of mechanical computer, called "Eiserner LI" or "iron LI"). They were mounted in U 555 for trials, and later in U 235, U 236, U 867, U 1017 and U 2511.
After the war, this (still mechanical) system was further developed and used in german Type 205, (I think) 206 and some 209 export boats, as well as in several french submarine classes, until they were replaced with modern electronic devices.

[Sailor Steve]

Originally Posted by JayDee

In good weather, a very good LI was actually able to make the boat hover without making noise at periscope depth (with the periscope raised). If he got the neutral buoyancy "almost right" by +/- a few kg, when e.g. the boat slowly sank deeper, the periscope going down in the water would add to the displacement - to the point where the buoyancy is exactly neutral.

I've seen that quoted elsewhere, but never the actual description. The only problem I can see with that method is that it means the periscope is up, and easy to spot, which doesn't exactly help with the avoiding detection part.

@Sailor Steve:

Not necessarily "modern" or "computerized", systems like that were developed during WWII by Friedrich Tuschka for a company called Askania (a kind of mechanical computer, called "Eiserner LI" or "iron LI"). They were mounted in U 555 for trials, and later in U 235, U 236, U 867, U 1017 and U 2511.
After the war, this (still mechanical) system was further developed and used in german Type 205, (I think) 206 and some 209 export boats, as well as in several french submarine classes, until they were replaced with modern electronic devices.

Interesting. Did this device actually balance the trim for hovering the boat? How long could depth be maintained without running the trim pumps? This is cool information.

[JayDee]

Originally Posted by Sailor Steve

Interesting. Did this device actually balance the trim for hovering the boat? How long could depth be maintained without running the trim pumps? This is cool information.

I had to look back in my literature... I try to translate the part:

For the new Bundesmarine submarines [Type 201 / 205], automatic depth control / hovering devices were developed by Tuschka Feinmechanik company, based on the last developments of Askania for the Kriegsmarine during WWII, working according to the principals of mechanical computers.
The device DT1 for automatic depth control kept the submarine at a given depth in all depths and at every speed, to disburden the crew during long continuing dived travel.
External interferences, like motion of the sea, currents etc. were counterbalanced by this device.

It was however more difficult to command a new depth via this device, because the pitch controller of the device counteracted the "new depth"-command, making depth changes quite slow.

The device contained a 5 kg pendulum to control the pitch of the submarine via the rear depth planes, and a diaphragm depth controller which controlled the depth via front and rear depth planes during slow travel. At higher speeds, the front depth planes were automatically retrieved, pitch and depth were controlled only via the rear depth planes. The actual mechanical computer for the depth and pitch controls contained multiplying devices, "sum levers" (sorry, no idea how to translate this) and "lead calculators" which computed the first and second derivation of the original sensor data, superimposing it on the original data.
The (adjustable) output signals of the device were assigned to the depth plane motors.

HDW commissioned Tuschka to develop a hovering device for the Type 205 submarines, which was completed in 1967/68. It was called DS 3 and should enable the boats to hover at a certain depth through flooding or pumping out water while the submarine was stationary.
This device was installed and tried upon U 11 and U 12, mounted starboard near the depth controlling device. It consisted of a target depth input device, diaphragm depth gauge, "lead calculator", solenoid valves for control air lines and diaphragm valves for flooding or pumping out water of the regulating tanks.

So I have to apologize: The true "hovering computer" did not come until the late 1960s (although it was still a mechanical device ), the "iron LI" was "only" controlling depth via the planes, which meant that the boat had to travel at least at slow speed.

Then again, if the boat was in a well trimmed condition, the "iron LI" (but a real LI as well) should have been able to do this also at slow speeds (silent running condition). Of course not, if the boat was damaged by depth charges and leaking.

EDIT: I may find some more info about the actual use of the Askania / Tuschka device in WWII Uboats in another book I have but right at the moment I am a little tired.. Tomorrow...

[smg13]

This might sound silly... but wouldn't it be possible to use a strong current and the planes to "hover", without using the engine propulsion? Would it be possible in the game?

[Sailor Steve]

@ JayDee: Thanks for supplying research. The more we learn about the technology of the time the more we can figure out what should or shouldn't be in the game. One can never have too much information.

Originally Posted by smg13

This might sound silly... but wouldn't it be possible to use a strong current and the planes to "hover", without using the engine propulsion? Would it be possible in the game?

No, because a submarine underwater is just like a balloon in the air. The boat will move with the current, so will in effect still be standing still. It's the same problem as you have with 'dead reckoning' navigation. Unless you have a shore reference you can't tell what direction the current is travelling or how fast, because you're travelling with it.

[postalbyke]

There is also a technique in modern submarining that would not be difficult to do with WWII technology, called "layer anchoring."

There is a place in most seas called "the layer." It's the depth at which the surface thermal conditions of the ocean give way to the thermal mass of the ocean, causing a slight difference in density. For depth control, one must match the boat's overall density (buoyancy) with the density of an area just above the layer, and when everything settles out, the boat will try to find this zone. This is probably what the LI took advantage of.

As to why one would do this, it's relatively simple:
It makes the boat as absolutely quiet as one is willing to be (ventilation fans secured, order the crew to the bunks).
It makes the boat very, very energy efficient.
And, if the layer is so kind, you may be in a spot that refracts active sonar around you

For more info on the layer, just google "layer depth"