XXI Elektrobrick

[Choronzon]

Greetings all,

I started a GWX 2.0 career in mid '44 to check out the XXI. I must say this is a nice boat with great submerged speed and handles nicely too except for a fatal flaw: it sinks like a brick at low speeds.

North of Scapa Flow, I ran into a convoy coming straight for me so I set myself up in attack position and took out an ore carrier and a large tanker before the escorts starting wetting themselves.

With 1000+ meters below my keel, I'd ordered a depth of 100 meters and silent run while I start to egress through the rear of the convoy at 1 knot. The escorts are falling further behind and I've made good my escape...until the crew starts crying about approaching critical depth and the gauge is hovering around the 160 meter mark.

Ok, fair enough, I must have slipped and accidently went a little deeper. Maintain depth and continue my escape. Nope, not happening. I'm still drifting deeper. Increase speed to 2 knots (the escorts are still close, so I don't want to attract their attention). Nope, still dropping and closing in on 300 meters now. I'm impressed with the depth capabilities of this boat, but I'm also getting close to needing a change of underwear.

Increase to 3 knots...damn, the escorts found me and I'm still dropping. Give it a quick boost to 5 knots, deploy a bold, and I start to rise a little but now the escorts are really getting excited, so back down to 2 knots. I've lost the little bit I gained and then some...getting close to 350 meters now and taking some hull damage. I'm entertaining notions of jettisoning the crew to lighten the load or surfacing at flank speed and running like Hell.

360 meters, more hull damage, change of underwear and still sinking...

I made it to 370 meters before the boat crumpled like so much aluminum foil. Pretty impressive depth, I must say, but a nasty way to die. Is it normal for the XXI to plummet at low speeds? I've never experienced this with the VII or IX boats.

Chor

[Albrecht Von Hesse]

By any chance did you load the game using SH3Commander? And, if so, did you have either malfunction or malfunction/sabotage enabled?

[Choronzon]

Yes, I did load the game through SH3Commander, but I don't have the sabotage/malfunction option enabled. Could it be something to do with thermal layers?

In hindsight, I spent a good amount of time at periscope depth either at 1 knot or stopped while I worked to get into attack position. No problems maintaining depth there. It seemed to happen when I went deep to avoid the escort cover, although I did that fairly slowly. No crash dive since they hadn't manage to find me yet.

Even leaving Bergen and travelling across to English territory, I had no problem maintaining periscope or snorkel depth.

Any other ideas?

Chor

[Heibges]

I noticed this sometimes in the stock game.

Did you hit crash dive then order silent running, before reaching the crash dive depth?

I have noticed that in any boat, if you change the depth manually before reaching desired depth, that the boat will slowly sink.

[Choronzon]

No, I never crash dived at all. There was never any need to since the escorts were well behind me when I was escaping. It wasn't until I started ramping up the speed to raise my depth that they even got close to me. Even after they found me, they weren't really that close; they were depth charging behind me. I'm pretty confident that if I could have stopped sinking I could have gotten away to thumb my nose at them from a safe distance.

Chor

[difool2]

A known issue, dunno if the GWX guys will be working on it.

[Choronzon]

Thanks, difool2. I guess I'll have to live with it and hope it doesn't happen too often. Kinda sucks to get a some decent tonnage and have it wiped out because the boat won't respond. Any idea if this happens only with the XXI? I've never had this happen in the VII or IX boats.

Chor
(http://www.subsim.com/radioroom/member.php?u=215818)

[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 ;)

[Kaptain Hans Wolf]

imagine a subsim where you had to trim all of the tanks yourself, now that would be tricky!

[Abd_von_Mumit]

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. :D

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. :up:

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.

[Gezur(Arbeit)]

"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])."

Nope, its like diffenrent temperatures with different depth, but once you reache the depth of 4° Celsius it will stay 4° and the water will not change its "wight" any deeper, thats what makes it more difficult to balance the boat. If you are over the 4° line you will climb/sink, till your boat is in the "balance depth"

Do you understand, what i want to say? ^^

[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 :o 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 :lol: