Sub Collision- How does this happen?

[Gator95]

http://news.yahoo.com/s/ap/20090216/..._sub_collision

For those who have any sub experience, how the heck does this happen? Don't you have an idea when you are a few hundred yards from even the most quiet sub that you've got a 'friend' nearby?

[JoeyGee]

"The two submarines came into contact at very low speed," Britain's First Sea Lord, Admiral Jonathon Band, said. Band, Britain's most senior naval officer, offered no further explanation.

But off the record, Band noted the French must have been heading towards hostile territory. If they were heading away, they would have been going much faster.

[LCHIEN]

the purpose of nuclear subs like these is to be an invisible, undetectable mobile launch platform in case the unthinkable happens.

In this case we have two western powers. who would have apparently similar launch objectives (various members of the soviet block, etc) should the need arise. They also have similar modus operendi - e.g try for quiet operation in unpredictable patterns -

It would seem that randomly roaming a large ocean would result in a low probability. But, in reality, like the fish tend to concentrate pollutants unexpectedly, the probablilities of collission are increased in ways that are unexpected.

1. the area of the ocean patrolled is similar becasue of the similarity of the targets
2. the depth is probably chosen to be the same since its common practice to pick a thermocline to hide below (that's a thermal layer that reflects sonar energy back down). If they both hide at this depth then This leads to increase probability since they are patrolling at the same depth.
3. Speeds are probably slow (that's what was reported), the slower they go the less noise.
4. No active sonar - this would give away their position - people can spot someone with a flash light looking long before the guy with the flashlight finds them.
5. Going under passive (listen only) sonar when two subs designed for ultra-quiet approach they can't hear each other. Its really like two guys stumbling around in the dark with slippers on trying not to make noise but find the other guy.
6. Like the satellites that collided in space, given years and years of continuous movement the odds eventually increase to one that a collision will occur. these powers have been patrolling subs in the atlantic since probably the 70's.- almost 40 years.

I considered that being "allies" they would each agree on an separate area to patrol
However, given spies and all and risking a multi billion dollar sub and security, I woud tell as few as possible. Limiting your areas of opertion just reduces the area your enemies have to look in to find and disarm you.

so as unlikely as it seems, it may have been inevitable.

What I wonder about, is how they figured out who hit who? They went crunch, counted their toes and fingers, thanked their luck stars, limped to their home port. Then what? Dial the French embassy,did anything funny happen to any of your ships last week? Not that anything happened to us....

[Uncle Cracker]

The problem with active sonar is that you gotta give yourself away to use it, so it doesn't get used all the time. Passive sonar ain't that great either, because you can hear everything within 1000 miles, and still not know where any of it really is.

[MilDoc]

"Both Saunders and Willett said submarines don't always turn on their sonar systems, or make their presence obvious.
"The whole point is to go and hide in a big chunk of ocean and not be found. They tend to go around very slowly and not make much noise," Saunders said."


I guess that explains it.

[Alex Franke]

They chase each other around out there, so I guess it doesn't surprise me all that much. Didn't the French say that they didn't even know they hit until later?

[jackellis]

It's not unlike the problem of mid-air collisions. If my math is correct, there's about 1.6 billion cubic miles of usable airspace over the earthbetween the surface and 40,000 feet yet there are several mid-air collisions, mostly between small aircraft, every year.

Most flights take place over land.
Aircraft tend to be bunched up around major metropolitan areas.
Aircraft flying from one place to the other tend to fly the same routes at approximately the same altitudes to minimize fuel consumption and flying time.

I have been turned off an airway (like a highway in the sky) so a faster airplane could pass me. Airplanes in front of me have also been turned away so I could pass them.

I have flown into the Truckee-Tahoe airport on several occasions when there were three or four airplanes of different sizes and speeds, all in line to land on each of two intersecting runways with no control tower to maintain order.

[LCHIEN]

The problem with active sonar is that you gotta give yourself away to use it, so it doesn't get used all the time. Passive sonar ain't that great either, because you can hear everything within 1000 miles, and still not know where any of it really is.

Actually passive sonar can be very powerful.
Active sonar detects objects at a distance and hears the faint reflections that weaken in both travel directions. Passive sonar listens to the noise of the object that is reduced only in one direction. So the range can be much bigger as well as not giving away location. In reality active sonar is almost never used anymore except to get a final fix for a kill shot when tracking a very quiet opponent.

The sonar used on nuclear subs is usually a towed array way behind the sub and hundreds of meters long. Its like a 1-2" diameter rope with thousands of microphones and amplifiers. Then they also have planar 2-D arrays on the sides of the sub. By combining the signals in array processors, the signal can be amplified and beam steered - its possible to get very small aperature and high gain same as can be done with antennas except the scale is much different.

By tracking the angle as the object moves and the sub moves, its possible to get a very accurate fix on the distance, heading and speed of the object. Furthermore object identification and speed is often determinable the sound characteristics and frequency of the blades.

You'd be surprised what the military does for sub sonars.

Alex, these were strategic ballistic missile subs. They don't go around chasing each other, they try to go around making no noise and avoinding anything that even smells like another sub, lest it be a hunter-killer. Now hunter killer subs go around looking for missile subs... try to remain undetected, follow them at a discrete distance, try to keep them at arms length, take them out with a nuclear torpedo if war breaks out before they get a salvo of nuke missles off.

[Richard in Smithville]

So how many bumps or near misses have happened in any navy but the general public never hears about it. I say bravo for coming clean on the incident.

[sparkeyjames]

By tracking the angle as the object moves and the sub moves, its possible to get a very accurate fix on the distance, heading and speed of the object. Furthermore object identification and speed is often determinable the sound characteristics and frequency of the blades.

Except when the searched for object is going very slow and has a sound absorbing hull. Apparently.

[cgallery]

Subs are always looking for other subs.

Place bags over the heads of everyone in a room, and ask them to find the other participants, and you're going to find clusters of people with bags over their heads, each stepping on the toes of one another.

[cwithboat]

Il es le coque. Je suis le renard.

[TB Roye]

The French sub zigged when he was supposed to zag. Or the british sub had to much port and forgot to zig. Sorry I had a little vino for dinner and a nice pork loin.

Tom

[sparkeyjames]

Il es le coque. Je suis le renard.

I don't speak French. Does that mean 'I surrender' ?

[LCHIEN]

Except when the searched for object is going very slow and has a sound absorbing hull. Apparently.

yes, exactly. And specially sound isolated machinery and very expensive non-cavitating, anti-vortex propellors, etc., etc., etc.
Becaiuse they are entierly underwater ander more hydrostatic pressure nothing cavitates, the entire hull is streamlined for subsurface so its possible to make subs very quiet. And they can hide under thermoclines that a surface ship can't.