Submarines: January 12, 2005

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The American nuclear submarine USS San Francisco hit an uncharted seamount on January 7th, killing one sailor and injuring sixty others, 23 of them so seriously they could not perform their duties. Facts about the incident were slow to emerge. It appears that the sub was traveling on a course it was ordered to follow, at a depth of 500 feet and a speed of about 56 kilometers an hour. This was the first time the navy had given the speed of a Los Angeles class sub as anything but 25+ knots (45 kilometers an hour.) It has long been believed that these subs could make more than 55 kilometers an hour. 

The visible damage to the sub indicated that the sonar dome at the front of the sub was partially collapsed, and, according to information released by the navy, some of the forward ballast tanks were damaged. The pressure hull was not compromised. The submarine immediately surfaced after the collision, which was apparently a glancing one, but it immediately slows the sub to about seven kilometers an hour. The crew had some trouble getting to the surface, because of the damaged forward ballast tanks (which hold water, that is rapidly pumped out, and replaced with air, to give the sub buoyancy and bring it to the surface.) The impact, of course, caught everyone unawares, which is why there were so many injuries. The sailor who died, had been thrown forward, hitting his head on a pipe. He died of that injury two days later. 

The captain usually losses his command after accidents like this, although in this case, that might not happen. If the captain was following all procedures correctly, and there was no way the seamount could be detected, the incident might not destroy his career. There are many uncharted underwater features, especially 500 feet underwater. The technology does not yet exist to economically chart all of the ocean bottoms to that, and greater, depth. Most waters are charted sufficiently to protect surface ships. But there are only about two hundred subs that normally operate at the depth this accident took place. There may be a call for the navy to change its procedures, and have the sub use more active sonar devices when traveling in certain waters. But this will generate protests, because active sonar disturbs the fish. There are also technical issues regarding how effective such sonar would be in avoiding all types of underwater collisions. Moreover, in wartime, you avoid using sonar as a navigation aid, as it gives away your position. Actually, traveling at high speed gives away your position, because of the noise generated by the propulsion system and water rushing over the sub. In wartime, the sub might have been moving at 10-20 kilometers an hour, which would have caused less damage and fewer injuries.

If the Navy adheres to maritime tradition, that calls for the naming of previously unknown underwater features after the vessel that "discovered' them, even if by running into them, the uncharted seamount will now be known as the "San Francisco seamount". 

Accidents like this are rare, but there will probably be a review of the charts, of underwater geography, that are used by American subs. This review process is standard whenever there is a major underwater earthquake or volcano eruption. For example, the December 26, 2004 earthquake off Aceh is known to have seriously rearranged the ocean bottom in that area, and efforts are already underway to update charts. But now an effort will be made to try and determine where there may be other potential "San Francisco seamounts". 


 


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