XXI Elektrobrick

[TomcatMVD]

Not an issue... your boat's buoyancy changes depending on the depth you're currently in, AFAIK, not modelled in stock but modelled by the GWX team.
IRL it was necessary to keep a certain speed to mantain your boat at a specific depth, I don't know if the GWX went to far modelling that or if it is actually accurate. Problem is, that if modelling that feature, maybe you should be also able to set your dive planes to a specific degree, since it might be quite annoying to have to order "surface" just to order "current depth" a couple of seconds apart.
All and all, I think this is what's happening to you, of course a GWX team member will be able to confirm or deny this.
Hope it helps!

[Storabrun]

Why were you going that slow to begin with? 2 knots is a good for a type VII or IX when you need to be silent but for a XXI you can double that speed.

[antikristuseke]

As it has been said, with a XXI boat you can really go a lot faster while still being unheard.

[Gezur(Arbeit)]

U probably just got into the sonar cone.... and i though max speed undetected while silent running is 7 knots

[Choronzon]

This is my first experience with the XXI, so I defaulted to 1 - 2 knots silent running the same as I do in the other boats. I wasn't actually aware that I could effectively double that and still remain silent.

When I gave a quick burst up to 5 knots to reduce the downward drift, the escorts seemed to get a little excited and started pinging me. I stepped back to 2 knots to try and lose them again and they lost the contact. Perhaps that was just a coincidence

Just for giggles, I restarted the career and tested depth keeping at various depths and speeds and found I had no trouble maintaining whatever depth I selected. So, I assumed it was just a one-off occurrence. Then I ran into another convoy and the original scenario repeated itself (I was watching for it this time, so I managed to get away without getting crushed.)

So, it seems to happen only when I'm near other ships at a depth of 100+ meters travelling at 1 - 2 knots. If there are no contacts in the area, I can dive deep and move slow without a hitch. That's sure gonna make convoy attacks interesting this late in the war. I'll keep playing around and see if I can keep reproducing it on a consistent basis.

Chor

[Grayson02sept1980]

had a similar experience with my VII!

Escaped after an attack going ALARM! (Crash dive) and once I had reached the crash dive deep I set it to 160m (I know the save deep is 150) and it dropped though I was setting the boat to go up....... and dropped (silent running) ...

till 180m... I was getting a bit nervous and gave it a boost all ahead flank and slowly got up with "boosting" my way up to 160 again..... then it slipped again.

Needless to say the escorts got hold on me and dropped their charges on me..

when I reached 150m with the same method it keept its depth.

But... But.... I must also add that I sent all crewmen to the back of the boat as I thought the people in the front part might be the problem.

maybe that's it. I also use SH3 Commander etc....

[Gezur(Arbeit)]

Its nearly impossible to balance a sub under water, its easyer in periscope Depth, but when the temparature of the water hits 4° Celsius it has the smallest distances between the Atoms, and the Water will never be colder in the depth, because of this. so u have to make the boot as heavy, as the water around it, and thats nealy impossible, so u need some speed to keep the depth.

Its a physical phenomenon. just like in real life

[msalama]

had a similar experience with my VII!

Me too. I was playing a single training mission skippering a VIIC, and had to dive deep in order to avoid a destroyer. I then ordered 250m and went to silent running. Well to cut a long story short the boat didn't stabilize until I had hit 262m, and then couldn't climb at 2kts A forward speed of 3kts did the trick however (the destroyer didn't pick me up for some reason) so I finally slipped away at 250m / 2kts...

Needless to say I was dripping with sweat after that wee incident

[Abd_von_Mumit]

Originally Posted by Choronzon

This is my first experience with the XXI, so I defaulted to 1 - 2 knots silent running the same as I do in the other boats. I wasn't actually aware that I could effectively double that and still remain silent.

When I gave a quick burst up to 5 knots to reduce the downward drift, the escorts seemed to get a little excited and started pinging me. I stepped back to 2 knots to try and lose them again and they lost the contact. Perhaps that was just a coincidence

Just for giggles, I restarted the career and tested depth keeping at various depths and speeds and found I had no trouble maintaining whatever depth I selected. So, I assumed it was just a one-off occurrence. Then I ran into another convoy and the original scenario repeated itself (I was watching for it this time, so I managed to get away without getting crushed.)

So, it seems to happen only when I'm near other ships at a depth of 100+ meters travelling at 1 - 2 knots. If there are no contacts in the area, I can dive deep and move slow without a hitch. That's sure gonna make convoy attacks interesting this late in the war. I'll keep playing around and see if I can keep reproducing it on a consistent basis.

As said, there are numerous factors influencing your bouyancy, one of them is water temperature (thus density/weight), the deeper the closer to 4 deg. Celsius, but also pressure (the deeper you go the less is your displacement, as the boat is compressed, as well as the air in tanks) water salinity and so on. It seems that whis was somehow simulated in SH3 (GWX?), as under certain depths boats tend to sink at slow speeds. :hmm:

In my VIIB/C speed of 2.8 knots was enough to gain positive trim, 2 was enough to maintain depth (zero trim), but not to go up. Just like planes - they tend to fall down when too slow.

As to the 'close to other ships or not' issue - did you test your boat bouyancy when running silent? There should be significant difference in performance (ability to maintain positive trim at slow speed included) between the two states. When running silent, any boat equipment producing noise is switched off, it could include also pumps for trimming tanks... :hmm: I doubt it was modelled, but one never knows - this game hasn't stopped to surprise me.

Originally Posted by Gezur(Arbeit)

Its nearly impossible to balance a sub under water, its easyer in periscope Depth, but when the temparature of the water hits 4° Celsius it has the smallest distances between the Atoms, and the Water will never be colder in the depth, because of this. so u have to make the boot as heavy, as the water around it, and thats nealy impossible, so u need some speed to keep the depth.

Its a physical phenomenon. just like in real life

Actually it would be the opposite - the heavier the water the easier to maintain depth/rise. At 4 deg. Celsius temperature water has the largest density (thus it's always 4 degrees deep in the sea [unless close to seismic regions]).

[Kaptain Hans Wolf]

i thought it was all so simple till i read das-boot, now i apreciate all the work that goes in to trimming etc.