'Hovering' Uboat is achievable ??

[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.

[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]

Originally Posted by vanjast

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.