Underwater signalling

[Radio Fixer]

Just finished a book called SS Ceramic by Claire Hardy. Its a enthralling read although not easy as a lot of it is anecdotes which can be repetitive.

She was built in 1912 and sunk by U-515 in 1942 west of the Azores. 655 lives were lost including woman and children, there was 1 survivor, sapper Eric Munday.

Now here's the part relating to the thread title and is in a chapter on how the vessel was built. I had not heard of this signalling method before; I wonder how effective it was?

   

U-505 returned in very bad weather, having been told to search for the Captain, Eric Munday in huge seas was virtually washed aboard.

Life as a POW was remarkably good for him as food and 'fags' were never in short supply. He worked outside and even got the officers in charge to let them discreetly buy a beer. His camp was in Upper Silesia which is I believe now partly in Poland and Czech (where he was).

Must have been a good man as after the war he answered sacks full of letters from relatives of lost souls.

Gary

[ed731pdh]

Certain sounds will carry for thousands of miles underwater, whales towards the North can quite often communicate with their counterparts at the bottom of South America. The trick is picking the right frequency that will propagate the distance.

US Navy used to signal their subs using a ULF frequency that transmitted a single note that was aimed at the recipient sub, the upshot was not data transmission but a request to come to periscope depth to receive data via satellite.

And then you have the mystery sounds, these ones really are interesting.

http://en.wikipedia.org/wiki/Bloop
http://en.wikipedia.org/wiki/Julia_(unidentified_sound)
http://en.wikipedia.org/wiki/Train_(unidentified_sound)
http://en.wikipedia.org/wiki/Whistle_(un...ied_sound)
http://en.wikipedia.org/wiki/Upsweep_(un...ied_sound)

http://en.wikipedia.org/wiki/List_of_unexplained_sounds

[Radio Fixer]

Sound even seems to carry much better on water, my wife reckons she can hear me shouting to close by mates when I'm a long way out to sea.

I presume SS Ceramic would have come to a stop to hear the bells and maybe cut the engines? Wonder if they had a message system ... see no reason why Morse wouldn't work ... might have been at a low data rate.

Gary

[Refugee]

The modern system is used to identify ships by the underwater sounds made by the engines and props.
These are dipped into the water from helicopters or fitted to submarines and can identify the engine type and gear ratio to the prop and the number of blades.
Diesel/electric propulsion is used on some types of war ship in order to make this more difficult.
They have even sold war ships to the enemy and then been able to listen for them when there is trouble and they know exactly what they are listening for.

[ed731pdh]

Not so modern as you think, try SOSUS.

[Refugee]

Yes it was all part of the cold war right from the start as a ship ID system for surface vessels.
Submarines were more of a challenge as they have electric motors that can vary there speed easily without giving away an easy acoustic signature.