[Catfish]

Hello,
you have to know about salinity and water temperature to adjust trimming all the time, but this certainly was not the duty of the captain or "Kaleun/Kaleu" (in german). This was done for trimming purposes at least twice a day or whenever it seemed appropriate - imagine traveling from the Baltic into the North sea, or even to the Caribbean sea.
Measureing temperature and salinity (which certainly interacts) was done for trimming purposes, not primarily to steer the boat in certain layers of the water to intentionally hide from searching warships.
It was well known by U-boat commanders, that e.g. before the U.S. coast there were salinity layers that disturbed the hydrophone of the boat as well as the hydrophone and ASDIC/Sonar of their hunters, and sometimes this helped a U-boat to hide. But as far as i know there was no device that showed a surrounding density all the time like it is done today.

Measuring seawater temperature is not the problem, as well salinity was checked exactly by a spindle floating in a water probe - quite simple but effective.

Greetings,
Catfish

[Rosencrantz]

Thanks for info, cat! Just one q: Isn't it possible to count the density using temperatur and salinity?

Anyway, you just confirmed my thoughts though.

-RC-

[Khayman]

I'm not sure it was well known.

Wolfgang Hirschfeld was senior telegraphist on the U-109 of Bleichrodt. Near Cadiz Bleichrodt saw some vessels through the periscope that were not reported by Hirschfeld who was on the hydrophones. A little later he was called to the bridge to explain why he didn't hear three British warships which could be seen dead ahead.

He said he couldn't hear anything on the hydrophones and Bleichrodt "told me to smash it up. He was in a boiling rage, unreasoning and unreasonable"

Since they had to get past the warships to refuel, Bleichrodt went under them. Hirschfeld started to hear them faintly and said "They can hear as poorly as we did just now. It must be to do with the water layers." Bleichrodt looked at him and said "Smash the bloody thing up I told you. but I'll have more to say about this when we're back in port".

He was true to his word. Hirschfeld had to go to the Signals Office of the 2nd Flotilla and explain himself. Thankfully for him other boats had reported poor hydrophone audiblity near Gibralter. They concluded it was the fast currents and water layers.

This was about June 1941. So before that you could pity the poor telegraphist who had to face his Captains wrath. "Telegraphy is s*it" was something Bleichdrodt said frequently.

[Catfish]

Hello,
but wasn't that the episode where the microphone fuses had all been flooded with salt water when they removed the panels ? :hmm:
Anyway it was not common to hide in layers of different salinity and density intentionally, but accidentally in a way.

Rosencrantz, if you have a spindle floating in water, and this spindle sinks into the surrounding fluid as deep as to show you something like "1,023" on its scale, you have the salinity and the density of typical sea water at the same time - if the spindle is calibrated at e.g. 20 degrees Celsius it will show the exact density if the water has that temperature. If the water is warmer or colder you still have the density, you only would need to recalculate all if you needed the salinity, and you would do that according to some tables. Colder means the spindle does not sink in so deep, warmer means it will sink in deeper. As well fresh or sweet water will let the spindle sink deeper, and the icy salty waters of the North Atlantic will make it float quite high in the water. The salty waters of the Dead Sea would make it float very high.

So what you always need is the density, since this changes with the temperature and amount of fresh water or better the salt/fresh water ratio, all you need is the spindle to read the density and thus adjust trimming. Don't know if that is understandable, err, a link:

http://www.madsci.org/posts/archives/dec96/848609315.Ph.r.html


Greetings,
Catfish

[Rosencrantz]

Hello Cat! Great you did look this conversation again! I don't wan't to start to be a problem but there is something what I don't understand:

First your wrote:

[Rosencrantz]

Yep! Thanks for the link, Cat. Easy to understand.

I'm just thinking, if they got equipment to get salinity and temperature = they got the density because that's pure mathematic after we know the temp. and sal.

I'll give my quess: It was the temperature they lacked. (I think USN boats got the "temperature tool" quite late in the war. Which doesn't mean, of course, that germans didn't got that earlier...)

Well, next to the uboat.net.

Greetings,

-RC-

[Heibges]

From the Uboat Commanders Handbook:

57.) As regards the condition of ASDIC in relation to the transmitting capacity of the water, it has been ascertained that the efficiency of the submarine-detecting gear is considerably reduced in sea areas with numerous layers of water.

a.) Formation of layes of varying density ("stratification") of the water of the sea occurs after a long spell of sunshine on a calm sea, and also in a high degree in places where there is a mingling of different types of water.............. Continual observation and measuring of water densities and temperatures are therefore important and indenspensible, for establishing the presense of "stratification" when submerging to considerable depths as a means of evading pursuit by position finding.

b.) In additon, position finding is very difficult, and almost impossible, in shallow water of varying depths (sand banks), where there are many wrecks, as well as in narrow bays (Norwegian fjords), as it is usually not an echo that is produced, but numerous echoes, which make it difficult to keep, but more especially to locate, the target.

[Torvald Von Mansee]

[Catfish]

Hello Rosencrantz,
i think you got it all right -
You can calculate salinity if you have density and temperature, and all other combinations, but all a U-boat needs to trim the boat after all is the density - so if you have a spindle floating in a fresh probe you can read from the scale which density the surrounding water has, and thus adjust trimming directly. If a spindle with a given scale of density (which is not automatically equal to the salinity) tells you a certain value you do not need temperature and salinity - just trim the boat according to the observed density - it already incorporates the other values.

If you had the exact salinity of the surrounding water, and the temperature, you could easily calculate the density - but density could be measured directly after all.
If you were in the Caribbean sea maybe you know the salinity for the Caribbean sea is 1,022 - when you use a thermometer to measure temperature you could theoretically calculate the density using the two values, but in reality there are a lot of exceptions depending on sea state, sun etc., so even if you knew all exact values the best way would still be to measure the density directly via spindles.

I take it there were several glass tubes with spindles in it which could be flooded and emptied all the time for testing. As well imagine a metal tube flanged to the inner pressure hull with in-and outlet and a thermometer in it - you can read the temperature of the surrounding water all the time. This tube certainly had two valves to cut off any water if the boat went really deep to prevent breaking of the glass tube that would not withstand a pressure of say 200 m.
Taking temperature is not the problem, but since there was no automatic device like in the later US subs, you would have had to thoroughly control changes of temperature and density all the time if you wanted to take any advantage of different layers for hiding.
As said before i never read of U-boat commanders who intentionally looked for layers of different salinity/temperature to hide - which certainly does not mean anything. Maybe this was thought of as top secret even after the war and the new confrontation during the cold war, so no one wrote about this.

I hope this makes sense

Greetings,
Catfish

[Rosencrantz]

Yep Cat! You (we) are right.
Germans didn't have a tool compared BT (bathythermograph). The only way to find out the temperature was to take external water in the boat using salinometer for that. Everyone can imagine the results = water temperature quickly changed so that was far out to be an exact method.
Diving officer could note the heavy layer if the boat was in good trim, but as you wrote, there is many parts affecting to layers so they change "all the time". Also, in North Atlantic conditions layers usually lay well down in maybe 600 - 1000 fts, in the depths out of normal operating depth of the boat, especially in early war time. In Pac the situation was totally different, boats could usually easily achieve the layer. So I was reading, it was common that on approach phase USN boat often used to dive to find out were layer laid and after attack just dived to under it and dissapeared.

But, once again we can see, how the germans did loose the "technical war". BTW, BT was a rather new invention and USN did research to find it to be very useful. By early -43 many of the USN boats got the BT.

-RC-