In January 1981 I was working on a Supply Boat offshore Tunisia, Oil rig reported a severe vibration in the drill string/casing. The drill string was pulled and casing was found severely dented. It was later reported that USS Birmingham Submarine steamed to Gibraltar and had experienced a sonar dome (The Bow) failure. Here is a photo, not mine, of the casing as it was pulled up.
Things on the boats are all pretty much on sound mounts these days. Under normal steaming conditions, dropping a hand tool is not going to give the boat away. If the boat is rigged for silent running, then ya aint gonna be working anyway.
And as already mentioned, all sonar is on passive.
The way that ships are loosing cargo containers these days, I would not be surprised if that was not the object. Most watch standers are on their feet and surrounded by all sorts of pipes, valves, brackets, cabinets etc. A good bump could throw a sailor into something hard and pointy, especially the guys back aft in engineering.
The sub was in the Mariana Trench. The trench is moving and changing, as evidenced by the many recent earthquakes and active volcanoes. Some of the movement is strong compression, as the toe of the Pacific plate moves west against the side of the Mariana Plate.
This compression ejected a large rock or rocks upwards. It must have been with considerable force, therefore speed, to be going up. This is what hit the sub.
Even with sonar proximity warning going nuts, a large speeding rock from below would be hard to avoid, and probably in the heat of the moment, difficult to comprehend, being such an unusual event.
If you struggle with the plausibility of above, consider an underwater landslide with bouncing rocks.
If the photos of the damage surface, the point and type of impact will be more obvious.
A Seawolf class sub striking a container doesnât quite equate to a good bump. Considering 9000 tons displacement at 35 knots having an elastic impact with a 40 foot container fully submerged at 77 tons, the resultant speed change is 0.0765 m/s, or roughly 0.15 knots. That would be noticeable, but only just so.
That would be the containerâs point of view, since it experiences a 17.9 m/s speed change after being hit by a close approximation of a brick wall. Ask yourself: if your ship hits a container, do you get knocked off your feet? My gut said no, which prompted the calculations.
Math:
Kinetic energy of the sub:
9000000 kg x (18 m/s) ^ 2 = 2916 MJ
Total mass after plastic collision:
9000000 + 77000 = 9077000 kg
Unknown velocity X expressed through known mass and energy:
9077000 kg x (x m/s) 2 = 2.916 MJ
Now we solve for x:
x2 = 2916000000 / 9077000
x2 = 321.25
x = sqrt(321.25)
x = 17.9235
Speed change:
18 - 17.9235 = 0.07651 m/s
EDIT: I just realized that Iâm off on the amount of kinetic energy, by a factor of 2, although that doesnât influence the result. Apparently Iâm not that good at math, either
Submerged displacement is about 12,000 tons and bear in mind that a submerged submarine is much like an aircraft and can be deflected up and down as well as left/right, and rolled easily to high angles or any combination simultaneously if it strikes an object. Itâs not the same stability as a surface ship.
It doesnât have to be a huge object if the sub is at speed and crew can be knocked from their feet from a glancing blow. Even at slow speed a collision causing a momentary heavy roll might be able to be later corrected but nevertheless injure people in the first seconds.
Youâre right, Iâve only ever been inside museum subs. If you tell me you used to hit containers all the time and you always broke your nose, Iâll believe you. It just doesnât make intuitive sense to me that such a big boat bumping into such a small object would cause such a jolt, is all.
@Jughead I didnât consider angular accelerations. Is there any record of subs hitting small craft and the like, that can be used as basis for a comparison?
Subs use charts to get around underwater. Itâs possible they struck an uncharted seamount. Itâs impossible to survey and update every square inch of ocean bottom. When I worked for NOAA, weâd occasionally find a new one while surveying. It would not surprise me with all the tectonic activity going on.
