'Hovering' Uboat is achievable ??

[vanjast]

Just a note for the Mods:

Busy reading U-boat, the reference book for the film Das Boot.

The author makes distinct reference to the chief of the boat being able to 'Hang by the Periscope' - which essentially is hovering at periscope depth with the scope extended with engines off, IF the sea conditions were suitable.

Another point made in the same paragraph is that the Chief boasted being able to trim the boat so well at any other depth, that it literally 'hovered', either sinking or rising very slowly. Depth control at this trim being by slow speed. The speed is not mentioned but all indicators point to less than 2 Knots.

There were differences expressed for years of the games existence, that the U-Boat couldn't 'hover' - This source being regarded as genuine, tells a very different story.

:)

[Herr-Berbunch]

It would require constant trim, just one guy walking about would shift it all to cock! I doubt it was ever done, not saying it wasn't, just I doubt it.

[Sailor Steve]

Please give the exact quotes. What conditions exactly were "suitable"? It's like the oft-quoted 4-second reload rate for the deck gun. It could be done, but never in actual working conditions.

Barring that, do they give an example in which it was actually done in combat?

[fitzcarraldo]

"Das Boot" is a great, superbe novel, but I don´t consider the book for technical references...

In fact, there are many (many) u boats veterans refuting the technical and historical references in the novel.

Best regards.

Fitzcarraldo :salute:

[TorpX]

The speed is not mentioned but all indicators point to less than 2 Knots.



I wouldn't consider this "hovering".

It was probably undesirable to be moving faster than 3 or 4 kts. due to periscope vibration, in any case.

[vanjast]

Some pages - there's quiet a bit of technical stuff in the book.
Some funny errors, maybe through translation, but it looks accurate enough :)

[Marcello]

Another point made in the same paragraph is that the Chief boasted being able to trim the boat so well at any other depth, that it literally 'hovered', either sinking or rising very slowly. Depth control at this trim being by slow speed. The speed is not mentioned but all indicators point to less than 2 Knots.Dynamic depth keeping at slow speed is normal.

The author makes distinct reference to the chief of the boat being able to 'Hang by the Periscope' - which essentially is hovering at periscope depth with the scope extended with engines off, IF the sea conditions were suitable.Neutral buoyancy is more of a theoretical condition than an actual one, in practice you are always going to have either positive or negative bouyancy, if only by a small margin. I suppose that for an u-boat hovering at periscope depth for a significant lenght of time would have indeed been possible in a calm enough sea, but it would have probably required a skilled operator and very frequent trimming and compensation (with all that these entail). Italian WW2 submarines had been equipped with an automatic apparatus for static hovering at shallow depths in the 1930s, but it was eventually removed during wartime refits as such capability was not worth the trade offs (noise etc.).
My two cents.

EDIT
Rereading the actual passage now I get it at last.They are referring to the use of the periscopes for buoyancy control. From what I read this trick was indeed used, but will only work for a limited amount of time, eventually you have to resort to pumping.

[vanjast]

Well, it is physically possible then to 'hover' by the scope or by continuous trimming (noise or no noise)

One thing I do notice in the book, is that the author is continuously jotting down notes of his experiences, and a lot of the items look technically sound.
The guy is not a technical person at this stage, so he might have some things incorrect (I've picked up a few items), maybe from memory.

There's a lot of technical info, between the lines, so to speak :)

[Sailor Steve]

That is some great information, and thanks for sharing it.

I do notice two things, though. In that description he specifically says it is impossible for him to trim the boat accurately enough, and the boat will rise or sink. So, no underwater hovering. Yes, you can do it by constant trimming. Guess what? The pumps make just as much noice as the motors at slow speed.

The second point is the "hanging by the periscope". It's a nice trick, but he does say "...if the sea is calm enough and the boat's well trimmed..." This means that if the sea is perfectly calm you can sit and wait for a convoy, or sit perfectly still trying to avoid the escorts, at periscope depth and with your periscope raised.

Good luck with that. :dead:

[Marcello]

The second point is the "hanging by the periscope". It's a nice trick, but he does say "...if the sea is calm enough and the boat's well trimmed..." This means that if the sea is perfectly calm you can sit and wait for a convoy, or sit perfectly still trying to avoid the escorts, at periscope depth and with your periscope raised.It does work but as far as I read it was something that will only work for a limited amounted of time anyway. Eventually you will need to compensate by conventional means as the volume provided by the periscope will only enable you to fiddle so much with buoyancy.

I did not consider the implications of the "scope extended" but once you think about it is quite logical. In effects the submarine is actually floating, albeit with very little positive buoyancy. This means that the u-boat can benefit from the equilibrium (precarious given forces involved but notheless real) inherent in such condition. Static hovering at depth of course wil require very careful compensation .

[Hitman]

A submarine is much like a balloon, perfect balance is theoretically possible but almost impossible in normal conditions. You are always reacting to the boat raising or sinking, and the most you can pretend to get is a quite steady condition, but some minutes later it will have sunk or risen.

There is one exception, though, and that is finding a thermal layer. Because the colder water below is more dense, you can actually have the boat rest on the "layer" that separates both areas by trimming it heavier than the upper one, but lighter than the lower one. It will not break the "surface tension", but you need a pretty heavy difference thermal layer to do that. This tactic is not unusually used in modern diesel-electrics and nukes, albeit at greater depths.

[vanjast]

There is a reference in the book (Hard to find 1 sentence in 400 pages) where it mentions the Captain hanging by the scope to nail an unescorted freighter.

But yes I'm aware of all the above, and the consequences.
I know NYGM models slow sinking (not sure about GWX ) to try simulate this, and the expense of battery power.

What I really interested in is when a calm sea prevails in SH3, to 'hang' in one position with no power for hours, listening on the hydrophone which should have a range beyond the horizon in such conditions, coming up when more oxygen is needed. Maybe this can be modded, with a basic minimal power drain on the batteries. This in effect would be a perfect ASW avoidance trick while waiting for something to appear - and even better for anti-ASW in perfect conditions.

Would be cool
:)

[Sailor Steve]

I know NYGM models slow sinking (not sure about GWX ) to try simulate this, and the expense of battery power.
GW originally had a slow rise, but it was removed for GWX. As with stock, unless you have some damage you can shut the engines down and hover for hours.

What I really interested in is when a calm sea prevails in SH3, to 'hang' in one position with no power for hours, listening on the hydrophone which should have a range beyond the horizon in such conditions, coming up when more oxygen is needed. Maybe this can be modded, with a basic minimal power drain on the batteries. This in effect would be a perfect ASW avoidance trick while waiting for something to appear - and even better for anti-ASW in perfect conditions.
You mean not at periscope depth, but deeper? Your own source says they couldn't do that. Anyway, the game already lets you do it.

[vanjast]

Sorry.. At scope depth - should have mentioned that !

Deeper.. naturally trudging along at 'neutral buoyancy' speed

[Sailor Steve]

Unless you're using NYGM, you should be able to do it. I think there was an 'unfix' for NYGM's 'Anti-Hummingbird' mod as well, but I can't even think what it might have been called. :oops:

[Hitman]

What I really interested in is when a calm sea prevails in SH3, to 'hang' in one position with no power for hours, listening on the hydrophone which should have a range beyond the horizon in such conditions, coming up when more oxygen is needed. Maybe this can be modded, with a basic minimal power drain on the batteries. This in effect would be a perfect ASW avoidance trick while waiting for something to appear - and even better for anti-ASW in perfect conditions.

But you don't need perfect balance to achieve that in a real submarine. If you get buoyancy close enough and trim on the heavy side, the result will be a very small sinking rate, so that you might spend hours to actually sink, say, 100 metres. Then when you are there you just add a bit of compressed air and there you go up again at slow rate. You can hover slowly for longer than your Oxygen supply will last ...

The problem is doing that at periscope depth, because the extension of the periscope is limited and near the surface there are many turbulences and disturbances, so you would need to do many more corrections.

[Marcello]

But you don't need perfect balance to achieve that in a real submarine. If you get buoyancy close enough and trim on the heavy side, the result will be a very small sinking rate, so that you might spend hours to actually sink, say, 100 metres. Then when you are there you just add a bit of compressed air and there you go up again at slow rate.It is my understanding that once you have negative buoyancy the sinking rate is going to increase as the hull gets compressed more and more as depth increases, creating a positive feedback loop. That is to be avoided, for safety reasons.
Normal procedure at least as far as I know, is that once you are below surface you compensate (emptying the negative tank or such) to achieve neutral/slighty positive buoyancy and keep depth dynamically.

[postalbyke]

From US Navy experience, it is possible to float at a specific depth without using pumps, etc., but that depth is typically not periscope depth. It will also vary (as stated before) by local oceanic conditions (which do change).

I felt that the NYGM model was very close, but I felt that being able to model a depth at which the ship could float (i.e. 50m or so) should be realistic.

I can't find the article right now, but I remember seeing this on the internet outside the USN, layer anchoring or some such.

Anyrate, check out thermal layer ocean on the google

[vanjast]

I've done a bit of 'data manipulation' in the ..\data\Zones.cfg file.

NYGM HummingBird

[PumpsXXI]
Multiplier=1.0
;Flotability=0.15 ->> Original value
Flotability=0.005 ->> change this value
.
.
.

Changing the Flotability to the above value I got the sub to sink about 50m over 12 hours which is sort of acceptable. The funny thing is that the sink rate is not consistent, and will even rise a little at arbitrary depths, but the sub generally sinks, albeit much slower. A speed of 1 knot will keep you more or less at constant depth at 245m, but you'll need two knots or more to bring the sub up.
Still testing and playing around...
:arrgh!:

[Sailor Steve]

Cool! I like that. :sunny: