Submarines - where??

gasdave

gasdave

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If the question I am about to ask is not sensible then I willingly accept appropriate reprimand..... :o

It occurred to me as I was sailing in a Clyde sub exercise area at the weekend that I'm not sure how I would know if there were subs near me. So here is the embarrassing question. Am I correct in assuming that they would not be "seen" on AIS when not otherwise trying to be militarily invisible? We had one surfaced about a mile behind us previously and it was not shown on our AIS. Do they transmit this way?

Second question is, would AIS work from an underwater source anyway, does it depend on depth, etc. if so? I feel I ought to know the answer to this but ain't sure!
 
Subs are most definitely NOT on AIS. I doubt if they'd transmit even if they were fitted when they were on the surface.

AIS is line of sight radio frequency transmission; Subs tend to use ELF (Extremely Low Frequency) carrier waves for communications as VHF doesn't have much range through water. They come to "periscope depth" inn order to use satcoms.

You just have to trust that their sonar will warn them of your presence on the surface, although there are more than a few fishermen who's express doubts about that.
 
I live an sail from helensburgh , navy do whatever they like , if they want you to see them , you will , but be sure these days they will hear see and god knows whatever other elctronical sense you .

Ais is transmitted by vhf radio , aint going to work underwater , though subs can pop up radio bouys etc
 
I imagine they do.

When I was at school in the late 60's some bright sparks ( Gwyn and a few fiends ) one year above me discovered radio works very well underwater. They got onto Tomorrows World or some similar TV programme). Upon which they were silenced under the official secrets act very quickly indeed ! He went on to work for the MOD ! I expect a knock on the door in the next few hours !
 
Definitely definitely won't work when they're submerged!

I don't know what their transmission habits are when on the surface. Other warships sometimes transmit (usually with just "UK Warship" or similar, rather than a name) and sometimes do not, depending on what they're doing.

Pete
 
Thank you, guys. It seems my assumptions were not so out after all. I knew about the VHF/line of sight/not good under water thing but must have had a niggling self doubt somewhere! Didn't know about ELF though. Yes, some warships definitely do transmit AIS - I had a whole convoy on my screen a couple of weeks ago in a lovely straight line, all just called "Warship" :-)
 
GrahamHR said:
I imagine they do.

When I was at school in the late 60's some bright sparks ( Gwyn and a few fiends ) one year above me discovered radio works very well underwater. They got onto Tomorrows World or some similar TV programme). Upon which they were silenced under the official secrets act very quickly indeed ! He went on to work for the MOD ! I expect a knock on the door in the next few hours !
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Hi Graham

Did they really get the OSA waived at them? I'm surprised by that, as radio wave propogation under water is an "open" secret.

B
 
To state that "radio" will work underwater or not is a bit misleading.
"radio" is the same stuff as light, Xrays, ultra-violet and infra-red. Would anyone claim that light "doesn't work" under water?

What changes is the distance that such an emission will propagate (or travel) underwater, and that change is with frequency.
Some frequencies will travel very well under water for hundreds of km, some are stopped by water in centimetres.

AIS is in the VHF part of the spectrum. That part is often designated as from 30 to 300 MHz. Marine band is in the area round 150-170 MHz. These frequencies do not travel very far under water, usually totally attenuated after just a few metres, but dependent on water density, salinity and transmission output power.

Its quite reasonable to say that AIS does not work underwater. There's no secret method to make it work, it's not an official secret, just a pretty well understood and researched bit of physics.
 
Many years ago there was some comment about subs in YM. I think the advice was that a sub would normally be aware of a yacht if it had an echo sounder in operation.
 
Whilst on the way from Plymouth to Fowey a couple of years ago, this popped 'UP' just off the coast near Looe:

DSCF3954.JPG


At first all we noticed was its perriscope ahead of us, and then it surfaced to show this image, and was no more than 200 meters away. Quite frightening in any boat, especially a 22 footer! I was glad that we were motor sailing as I believe the sound of a boat's engine can be detected by subs. We wouldn't have had the echo sounder on at that time, but perhaps we should leave it on at all times??
 
Appledore said:
Whilst on the way from Plymouth to Fowey a couple of years ago, this popped 'UP' just off the coast near Looe:

DSCF3954.JPG


At first all we noticed was its perriscope ahead of us, and then it surfaced to show this image, and was no more than 200 meters away. Quite frightening in any boat, especially a 22 footer! I was glad that we were motor sailing as I believe the sound of a boat's engine can be detected by subs. We wouldn't have had the echo sounder on at that time, but perhaps we should leave it on at all times??
Click to expand...

When I worked in a shipyard building subs one of the commissioning engineers was ex RN and he said they picked up the QE2 coming out of new York and they where 3000 miles away.
 
Small vessels under sail probably represent the biggest identification problem to submarines. The sonar devices are incredibly sensitive and it used to be a standing joke that a Nuke in the northern approaches could pick up a porpoise fart in the Bahamas on it's passive sensors and tell if it were male or female. However, it is not for no reason that subs close proximity to home waters surface before moving inshore. They also pick up relatively noisy surface vessels as escorts. Again rumour has it that there's a tug in the Clyde with a chipped prop, kept specially to mask the running noises of the bombers.
 
Appledore said:
Whilst on the way from Plymouth to Fowey a couple of years ago, this popped 'UP' just off the coast near Looe:

DSCF3954.JPG


At first all we noticed was its perriscope ahead of us, and then it surfaced to show this image, and was no more than 200 meters away. Quite frightening in any boat, especially a 22 footer! I was glad that we were motor sailing as I believe the sound of a boat's engine can be detected by subs. We wouldn't have had the echo sounder on at that time, but perhaps we should leave it on at all times??
Click to expand...

At the risk of being a pedant I'm afraid that Trafalgar Class hasn't 'just' surfaced. A couple of giveaways: 1. The casing is remarkably dry (but it could be a red-hot summer day so I'll give you that one).
2. The SL72 (secondary) radar is rigged (white 'blob' up and left of personnel at front of the fin) - it takes at least 30 minutes of faffing to fit that - probably closer to an hour.
 
stuarta said:
At the risk of being a pedant I'm afraid that Trafalgar Class hasn't 'just' surfaced. A couple of giveaways: 1. The casing is remarkably dry (but it could be a red-hot summer day so I'll give you that one).
2. The SL72 (secondary) radar is rigged (white 'blob' up and left of personnel at front of the fin) - it takes at least 30 minutes of faffing to fit that - probably closer to an hour.
Click to expand...
Give the man time to find his camera; you never have them when you want them...

While sailing past Plymouth last year (big anti sub excercise underway) I was amazed at how fast they could go on the surface.
 
Camelia said:
Give the man time to find his camera; you never have them when you want them...

While sailing past Plymouth last year (big anti sub excercise underway) I was amazed at how fast they could go on the surface.
Click to expand...

They're not easy to spot when you're in the cockpit and only about 3 feet above the waterline, LOL! Certainly this one was manoeuvring all over the place. One minute broadside on, then dissapearing astern, and poping up off our port quarter. I can't comment on the radar or personnel, but she certainly disappeared astern of us.

I'll certainly keep a sharper lookout along this coast (yes, I do know it's a Sub Excercise Area).:o
 
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