Realism- and gameplay-related hardcode fixes for SH3.EXE

[Tom]

Originally Posted by Hitman

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.

This would be absolutely fantastic.

I found one more bit of information on buoyancy, in the U-boat Commander's Handbook:


181.) Always go down dynamically to a low depth! Flooding is a mistake: The submarine automatically becomes heavier with increasing depth (leaking of the stern stuffing boxes and other openings, reduction of volume (contraction) of the body of the submarine) and it may well happen that it drops to a greater depth than is intended. Consequently in diving to considerable depths, the maximum engine power should be used, and it is even advisable to pump out the boat (for example, in the case of Type VII, approximately 1 ton).


The way I read this, is that the boat loses 1 ton of buoyancy by diving to considerable depth (150-200 meters?). It is impossible to say what amount of this is caused by leaking and what amount by hull contraction. I would assume most of it is due to hull contraction, because even 1/10 ton is 100 liters of water, which sounds like a huge amount to just leak in.

So if a realistic buoyancy model is ever coded, changes caused by submarine depth might well be estimated as 1 ton of buoyancy for 150 or 200 meters (for a type VII).

Does anyone have numbers for real trims used, that is, how much positive buoyancy was normally used? Or any estimates of normal leakage figures for various depths? With these numbers it might be possible to calculate if a submerged submarine losing power and compressed air would actually rise to the surface or sink due to losing positive buoyancy from leakage.

[LGN1]

Hi,

I agree with Tom's previous posts. I think the best behaviour would be if you automatically surface when out of compressed air and electric power. I think this would have happened back then (at least if the commander and LI were responsible persons).

BTW, has anyone ever been in this situation in SH3 (no compressed air, no electric power, and escorts above so that surfacing is not possible)

Cheers, LGN1

[Hitman]

The way I read this, is that the boat loses 1 ton of buoyancy by diving to considerable depth (150-200 meters?). It is impossible to say what amount of this is caused by leaking and what amount by hull contraction. I would assume most of it is due to hull contraction, because even 1/10 ton is 100 liters of water, which sounds like a huge amount to just leak in.

I just double checked with the original german version and the translation doesn't seem to get the correct meaning IMHO. I think that what it means is that you should have up to 1 ton of positive buoyancy when deep diving, i.e. the boat should be trimmed to weight 1 ton less than what would sink it. In a 780 tons boat this is a tiny figure, but enough to ensure that dive planes keep the boat down and take account of leaks, etc. I think that BDU probably also considered that the boat would take in water if depth charged, so preferred that captains had reserve positive buoyancy in any case. Remember that BDU also wanted them to surface as quick as possible and engage again.

[Tom]

Originally Posted by Hitman

I just double checked with the original german version and the translation doesn't seem to get the correct meaning IMHO. I think that what it means is that you should have up to 1 ton of positive buoyancy when deep diving, i.e. the boat should be trimmed to weight 1 ton less than what would sink it. In a 780 tons boat this is a tiny figure, but enough to ensure that dive planes keep the boat down and take account of leaks, etc. I think that BDU probably also considered that the boat would take in water if depth charged, so preferred that captains had reserve positive buoyancy in any case. Remember that BDU also wanted them to surface as quick as possible and engage again.

Ok, so the 1 ton in the text is a suggestion for suitable positive buoyancy, not the amount of water that should be pumped because of hull contraction when diving from, say, persicope depth to 200 meters?

If this is correct (and my german is so bad, that I'll just take your word that it is), then please ignore my previous post about the amount of buoyancy change caused by water pressure change.

If someone will work on a realistic buoyancy model some day, this suggested 1 ton positive buoyancy will be a useful figure of what trim to use, at least for deep dives. Near the surface they might have used a lower figure?


Edit:
@h.sie: Please let us know if you feel we're hijacking your thread to discuss something that will never (or at least in the foreseeable future) be included in your fixpack. The technical details of buoyancy can well be discussed someplace else too. (Although I feel I've already input everything I know on the subject).

[Obltn Strand]

Originally Posted by LGN1

Hi,

BTW, has anyone ever been in this situation in SH3 (no compressed air, no electric power, and escorts above so that surfacing is not possible)

Not exactly but close. My sub took heavy damage and batteries sustained it lot too. It was during LRT mod times when fighting flooding was really slow. I had to blow ballast repeatedly and keep up high speed to avoid sinking. After some one and half hours batteries dried out and I used last pa to surface and scuttle the sub via SHC.

[Leitender]

Always go down dynamically to a low depth!

Dynamically means to maintain positive buoyancy and to steer with the rudders against this buoyancy to get a stationary balance. This also works the other way round. So, whether the boat sinks or rises when out of batteries and CA only depends on the current status of buoyancy.

[h.sie]

@Tom: I think that I won't try to change the whole bouyancy model.

One reason is, that even in the very basic question:

"what happens when boat is submerged and batteries and compressed air are exhausted?"

we have completely different opinions here!

I'll also leave this issue untouched until facts are more clear. Saves me a lot of time.

[Hitman]

Ok, so the 1 ton in the text is a suggestion for suitable positive buoyancy, not the amount of water that should be pumped because of hull contraction when diving from, say, persicope depth to 200 meters?

Yes . Regarding how much volume reduction the hull will suffer at X depth, this is something I haven't yet found figures of. Perhaps we could ask in the other thread that Reallydedpoet hinted at. In any case, it's hard to imagine that it can be very much. Existing yes, very noticeable, I don't think so.

Dynamically means to maintain positive buoyancy and to steer with the rudders against this buoyancy to get a stationary balance. This also works the other way round. So, whether the boat sinks or rises when out of batteries and CA only depends on the current status of buoyancy.

Exactly. As we know, boats were trimmed positive as a general rule, and kept at desired depth via dive planes (Which will only work >2 knots). However, when they dove deeper, leaks started appearing, hull compressed, etc, and the end result was that sometimes even negative buoyancy appeared. The 1 ton figure indicated by BDU tells us that, unless damage from depth charges and heavy leaks appear, 1 ton aditional weight via leaks would take quite a long time to build up, so it was deemed as a safe figure to ensure quick operational status to resurface and resume the engagement, instead of having to resort to the much longer and energy (Battery) consuming procedure of raising the boat via dive planes only and against the negative buoyancy.

BTW, actually and to complicate things even a bit more, the perfect buoyancy model should take into account that the higher the difference between neutral and current buoyancy for a given depth & weight (Read: water that had leaked in) the higher the forward speed you need for the dive planes to actually lift (Or sink) the uboat. There were no doubt times when using the noisy pumps to throw out the leaking water would be less bad than having to use flank speed to allow the planes to actually generate enough lift to raise the uboat with the aditional weight of the leaked water -thus exhausting the battery much quicker than with the pumps

[Tom]

Originally Posted by Hitman

Yes . Regarding how much volume reduction the hull will suffer at X depth, this is something I haven't yet found figures of. Perhaps we could ask in the other thread that Reallydedpoet hinted at. In any case, it's hard to imagine that it can be very much. Existing yes, very noticeable, I don't think so.

I wouldn't be so sure of that. I just found a book called "Concepts in Submarine Design", Cambridge University Press, 1994, which can be found (and read) at books.google.com. On page 38, this book states that:

"The consequent buoyancy loss at full diving depth can be reckoned in tens of tonnes in a submarine of 2000 to 3000 tonnes submerged displacement."

Of course, this statement is about modern submarines, which dive deeper than WW2 subs. On the other hand, the pressure hull is stronger in modern subs and, I would assume, resists contraction better. I think it is safe to assume that the buoyancy loss for a type VII at 200 meters is of the same magnitude, that is, a percent or two of submerged displacement. In any case, we're speaking of a figure of several tons, perhaps even over 10 tons.

[Hitman]

A figure of f.e. 25 tons in a 2500 tons submarine, as stated in the example, is 1%, which would amount to 7,8 tons in a 780 tons boat. So you might be right on that, however note that this is probably for some 400 metres depth, while uboats rarely ventured over 200, and that the curve for steel tension and flex is probably not linear, i.e. it will flex little at the beginning and then begin to flex a lot as pressure increases. Another thing to bear in mind is that modern subs are single hull.

I wish that someone with better knowledge of mechanics would come and ilustrate us

[PL_Andrev]

Hello

Do you know the mod (or plan it / discuss it) what happend if uboat lose all its fuel?

I think about some scenarios, but maybe is it already solved?

Originally Posted by Antar

Hello

Do you know the mod (or plan it / discuss it) what happend if uboat lose all its fuel?

I think about some scenarios, but maybe is it already solved?

Even if so, in SH3 you can continue your patrol using electric engines. SH3 has a bug. Even when diesels are not working your batteries can recharge mystical way while you on surface

[Olamagato]

In addition, I do not think that was correct, that you can use damaged both diesels before they are repaired. I had a situation that air attack destroyed two electric motors, and damaged two diesels. But I could swim on the surface. And also with the snorkel.

[h.sie]

@Olamagato: Put on the Todo-List - together with all this compressed air, battery and diesel supply stuff. Maybe, I'll look at it at a later time.

By the way: Using the DieselDamages Mod, you now risk critical damage or total loss of the diesels, if you force damaged diesels to do more than "Ahead Slow".

---

@THOSE_WHO_ARE_INTERESTED: Currently, Makman, Rubini and me are working together on an issue that was bothering us for years: Vampire night view: Ships are detected by the watch crew at far, far distances (more than 14000m) at completely dark nights, while the ememy cannot see your Uboat at a distance of some 100 meters. I'm slightly optimistic now that we find a solution.

After that, I'll assemble all the Alpha-Testing Mods into V16B, including some requested changes (e.g. repairtime adjustable via .ini file and 20m diving sufficient to reload internal torpedoes in storm) as well as some small bugfixes.

[Jaeger]

good news, h.sie. i wish you all a good progress in this annoying issue.