"Driftdown problem" (neg. buoyancy when submerged) addressed?

[senjorlossi]

Hi Guys,

I completed a patrol tonight and got both a new sub (VII C) and some promotion points. I gave it a try and gave the navigator some intensive training.

Now I am able to hold the depth at 150 m at slow speed without problems. Couldn´t check any deeper, since I am still in the north sea on my way to the western approaches, but the problem of sinking to death seems to be fixed now.

Don´t know if it´s the new boat or the navigator´s skills, but finally I´m able to sneak away deep and slow.

[Rip]

Originally Posted by Morpheus

Very nice explanation, thx

Well except that Main Ballast Tanks are normally fully flooded when submerged. the tanks used to trim the boat for varying water conditions are internal to the hull and therefore air compression plays no part. Although the pressure does have an effect on the trim and drain pumps as they must overcome sea pressure when trying to lighten the boat. Inversly it can be quite easy to increase the weight of the boat by simply opening a valve and letting the pressure do it's work.

Modern submarines have a system for hovering that involves two tanks one for flooding that is vented and one for blowing ballast that would be pressurized. A large three way ball valve can be hydraulically positioned to quickly gain or loose ballast to maintain depth without any forward speed.

Rip

[Frederf]

Oops, yeah MBTs would have no effect on trim being full for diving. Are there any instances of partial MBT usage like decks awash?

[Rip]

Originally Posted by Frederf

Oops, yeah MBTs would have no effect on trim being full for diving. Are there any instances of partial MBT usage like decks awash?

I don't think so. Mostly because as you noted as you descend the air compresses and you loose buoyancy. Putting yourself in a position to loose more buoyancy as a simple function of descent than what nature already mandates would not be prudent.

In fact at least on submarines I have been on we left MBT vents open for some time after submerging to ensure there was as little air in them as possible.

Rip

[Kromus]

Originally Posted by senjorlossi

Hi Guys,

I completed a patrol tonight and got both a new sub (VII C) and some promotion points. I gave it a try and gave the navigator some intensive training.

Now I am able to hold the depth at 150 m at slow speed without problems. Couldn´t check any deeper, since I am still in the north sea on my way to the western approaches, but the problem of sinking to death seems to be fixed now.

Don´t know if it´s the new boat or the navigator´s skills, but finally I´m able to sneak away deep and slow.

Yes, VIIC isn`t affected as much as other subs somehow, I tried historical missions just to dive as deep as possible and it could hold depth same as yours...
Maybe some modding guys should look into this how they made this in VIIC possible? VIIB has very big problems holding even 50 m (falling to 55-57 at low speeds) and VIIA is little bit better.

[Kumando]

No this is definitely a bug i cant trim the boat at a mere 30 mts it keeps going down the only depht that the boat maintains its periscope depht.

[thruster]

i always thought that the uboats were maintained intentionally abit heavy. you couldnt stay stationary whilst submerged and still maintain your depth. i thought it was related to avoiding breaking the surface once the weight of the torpedo left the tube, or as fuel weight decreases as its burnt off, etc.

bouyancy was maintained by continual weight management, ballast juggling and importantly for uboat designs; forward momentum over the dive planes.

.....or have i missed something?

[JamesT73J]

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

[BlackSpot]

Originally Posted by JamesT73J

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

Hmmm possibly. I'm using the morale mod and I'm not getting any drifting

[sergei]

Originally Posted by BlackSpot

Hmmm possibly. I'm using the morale mod and I'm not getting any drifting

Really. Which one? I'd like to try it out, but there are now a few available.

EDIT: I think you mean this one?
http://www.subsim.com/radioroom/down...o=file&id=1568

[elve84]

I would say its normal behavior for a sub, subs don't only use balast tanks for keeping debt, they also use there dive planes for this, as you hang stil in the water there is not water going over ya dive planes and thus ya can't maintain your debt. add that up with the balast tanks leaking and no working pumps because you as you are running silance. I would say it is normal that your boat "sinks" deeper.

As the Type VIIC is more modern, it could verry well be posible that german engeneers found a way to keep better debt with this ship. That would make the game more realistic in my opinion and historicaly correct.

[BlackSpot]

Yes Sergei, I just checked.
I tested the drift last night. Went down to @ 180 m it stayed steady even when using time compression x 32. Now, whether it's the mod effecting this, I can't say.

[Frederf]

Originally Posted by Rip

I don't think so. Mostly because as you noted as you descend the air compresses and you loose buoyancy.

I picked decks awash as an example since you're obviously not diving so it might be OK to have partial MBTs.

Originally Posted by thruster

I always thought that the U-boats were maintained intentionally a bit heavy. you couldn't stay stationary whilst submerged and still maintain your depth. i thought it was related to avoiding breaking the surface once the weight of the torpedo left the tube, or as fuel weight decreases as its burnt off, etc.

Buoyancy was maintained by continual weight management, ballast juggling and importantly for U-boat designs; forward momentum over the dive planes.

.....or have i missed something?

Read above posts, said basically as much and you're right. The difference between that and what SH5 does is a U-boat in real life settles a little bit to its trimmed depth which may be 10-20m below where it wanted to be with planes while SH5 will just settle and settle and settle and settle very, very deep.

Originally Posted by elve84

I would say its normal behavior for a sub, subs don't only use ballast tanks for keeping debt, they also use there dive planes for this, as you hang still in the water there is not water going over ya dive planes and thus ya can't maintain your debt. add that up with the ballast tanks leaking and no working pumps because you as you are running silence. I would say it is normal that your boat "sinks" deeper.

As the Type VIIC is more modern, it could very well be possible that German engineers found a way to keep better debt with this ship. That would make the game more realistic in my opinion and historically correct.

Settling is normal, settling 100m+ is not. Who says ballast tanks leak or that silent running is on?

[Kromus]

I found solution for this. Looked at VIIC values at goblin editor and tweaked them little bit for VIIB....

After you load everything you need (GR2 and sim files) look for:

unit_submarine
obj_hydro

change this:
mass to 620.8
surfaced displacement 629/draught4.55
submerged 730/draught6.4

With these values I could hold depth at 160m w/o moving!

I hope this helps a bit.

It definately needs more tweaking but I think it`s a good thing to start with.

[Rip]

Originally Posted by JamesT73J

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

Actually modern submarines are able to hover. Now whether this is realistic to a u-boat I cannot speak. But hovering is a critical skill in under ice operations. The places you can break through the ice are not always large and you must ascend and a very controllable rate.

I would say they could certainly trim the vessel to at least able to maintain depth with not much over 1 KT. Doing this at periscope depth would be much more of a challenge than say 50M.