Aargh, I must admit that I really forgot about active bouyancy from dive-planes.

4 variables: dive-planes, batteries, pumps, compressed air.

problem too complex :)

I better restrict on programming instead of thinking about Uboat technology.

Fortunately, there are some competent guys to help me.

I´m sorry guys, again i wasn´t right: 1atü = 1at + 1. 1at=10m WS (10m water column), so 1atü is the pressure in 10m depth. "at" is called technical athmosphere, whereas 1atm = 760mmHG, what is called physical athmosphere. The then used value was "atü". So with a storage of 200atü, tanks can be blown at at depth of 200m.

To come back to the initial question:

If i´m correct, the compressor won´t work without electrical energy. So, when the battery is empty, and CA-Tanks are also empty, you shouldn´t be able to submerge (edit: sorry, wrong. I meant surface) . Has anyone ever tested whether the compressor works when submerged and then fills up the CA tanks (I don´t think so), and ends if the batteries are emptied?

It seems, that many things are still unknown in this game...

Ok, after reading the VIIC manual and the reports of americans who examined captured u-boats more closely, this is how I understand pumping and blowing water out worked:

The main ballast tanks (about 103 cubic meters), main ballast and reserve fuel oil tanks (49 m3), and negative buoyancy tanks (quick dive tanks, 4 m3) were to be blown, not pumped.

The regulating tanks (15 m3) and trim tanks (7 m3) could be pumped or blown, and the regulating reserve fuel oil tanks (9 m3), as well as the torpedo compensation tanks (14 m3) could only be pumped.

Pumps were also used to drain water that had leaked inside the rooms and bilge of the submarine.

The main method of gaining positive buoyancy in order to surface the boat was blowing of the main ballast tanks. The tanks were not blown empty, only enough was blown to start the boat rising. As the boat would become lighter as it rose, it rose all the way to the surface unless more weight was later taken on board. When the conning tower was above water, the diesels were started, and diesel exhaust was then used to blow the main ballast tanks empty.

When diving deep, one of the regulating tanks was kept at a pressure of 12 atm or so, to enable pumping of water out even when the depth was 200+ meters. The idea was to pump water that had leaked inside the boat first into this regulating tank, with a pressure difference of 11 atm (12 atm in the tank and 1 atm in the boat), and then from the regulating tank to main ballast tank 3 (or directly off the boat), with a pressure difference of another 11 atm if the depth was 230 meters, for example.

Thus, if blowing the main ballast tanks was not possible for whatever reason, the water possibly inside the boat and inside the regulating and trim tanks could be pumped out in order to surface the boat.

The VIIC had two compressiors to create the compressed air, one working on diesel, one on electricity. Earlier boats (VIIB) had two electric compressors. Compressing air, if I understand correctly, could only be done on the surface anyway, because the air had to come from somewhere, and that somewhere is from outside the boat.

Very sophisticated and informative posts, Tom. Thank you very much.

The power of the compressor is btw. given as 205kg/cm^s what is 205atü (205 technical athmospheres beyond normal air pressure, not physical atmospheres: "atm"). Main pumps worked against 105mWS what is 10,5atü. The auxiliary pumps´ maximal pressure is declared as 10atü. So both obviously have the same max pressure, the difference is the power of 385l/min. (aux.) vs. 500l/min.(main).

I agree, so surfacing should not be possible when batteries AND compressed air are empty, should it?

Getting confused...


Edit: Maximal blow out pressure is given at 25atü. That´s enough for getting positive bouyancy at a depth of 250m. If CA reserve is full, this should make the boat able to surface 8 times from its deepest depth. Correct?

Surfacing is only possible with compressed air regardless of full or empty batteries...

..since there's nothing to compress for the compressors whilst the uboat is submerged [except the crew's breathing air <- no good idea].



.

You've to consider that the pressure of CA decreases during every blowing act.

I believe even if you have a negative static buoyancy, you can generate a positive dynamic buoyancy by using propulsion and rudders (if batteries are not empty, of course). That´s not sufficient to keep the boat at the surface when it stands at 0 knots, but surfacing is possible, imho. This is called "stationary" balance. Theoretically, i know. But planes are heavier than air, too, and though they´re able to fly, because of the stationary dynamic balance.

205atü ./. 25atü = 8,2. If you order "surface" for 7 times, there should left a pressure of 27atü. Ok, that´s maybe not enough for transferring further ballast outside the boat, because the remaining difference in-out is only 2 atü. But 7 times, it should work.

I don't think so.
The efficiency of the diving planes decreases the more the uboat rises since it's weight is too heavy [the efficiency also depends on the uboat's speed - but the speed is limited]. There's no other way than to lower the weight of the uboat by blowing ballast; after that the diving planes will take some more effect again.

Keep in mind that diving planes are not able to create that ascending force like aircraft wings.

After reading all these posts I am more confused than before.

But one issue is obvious:

If
- Boat is submerged
- batteries and compressed are exhausted
the diving tanks cannot be emptied.

But exactly this is possible in the game.

This I try to fix in the next time.

Yep, that has to be fixed.

I think even for The Old Man it was a hard work to build all these difficult RL physical laws and buoyancy behaviors, so it's nearly impossible to emulate them all in a sim... ;)

So game is 100% over when Boat is submerged and batteries and CA are exhausted. No chance to surface.

For that hopeless situation, I have an idea: To give the player back a little hope, and make the game more interesting, I could program a minimal chance (5% ?) that the LI is able to cunjure up some little battery charge out of his hat, before the O2 supply also is exhausted......a little bit of "Das Boot".....

would be a very easy addition.

This is true. Gaining more buoyancy by losing weight is only possible with either compressed air or electrical power.

However, the fate of the unlucky submarine finding itself underwater without power or compressed air depends entirely on its current buoyancy and any possible leaks.

If the boat has positive buoyancy and no leaks, it will rise to the surface on its own. As a submarine rises it gains more positive buoyancy, so the rise will initially be slow but gradually faster. The reason for this gain in buoyancy is water pressure. The deeper the submarine is, the more the hull is compressed, and the less water it displaces. The actual weight of the submarine does not change, of course. Same weight, more displacement -> more buoyancy.

Normally submarines are trimmed to have a slight positive buoyancy underwater. Depth is kept by using the dive planes to apply a small force downwards, offsetting the upwards force caused by the positive buoyancy. Thus, with loss of power and compressed air, the submarine will eventually rise, unless it leaks so fast that buoyancy, at any point, turns negative. If this happens, down it goes, and nothing can be done about it.

Only if the boat has negative buoyancy, due to leaks. If it has positive buoyancy (which is normal for submarines underwater) and is not leaking, it will surface eventually.

Very good sum-up Tom, I agree to your conclussions :up:

That is actually realistic, as what we have in the game as empty battery is more like the fuel tank of a vehicle. But batteries are not like that, you can squeeze a bit more energy out of them if you let them recover for a period, and you could also in desperate situations even try to interconnect cells that are not discharged to make them work together bypassing those empty which would normally suck energy instead of giving it back. :up:

In any case, I think that even if you limit your programming to the clearly identified things, it is worth to continue the discussion because we might end up agreeing on a reasonable model for boat buoyancy that can be later implemented. This would allow fixing things like the humming bird situation, etc.

I am sure most of you have seen this thread, but it is a great one related to submarine history and technology. It is from the main SH4 Thread.

Here

A lot of discussion on Fleet Boats, but I am sure there is some discussion related to other types of subs. And some of the info discussed would apply I am sure to more than one type.