Berkeley CSUA MOTD:Entry 35623
Berkeley CSUA MOTD
2021/06/19 [General] UID:1000 Activity:popular

2005/1/9-10 [Science/Disaster, Science/Space, Politics] UID:35623 Activity:high
1/9     What does "run aground" mean? -silly sodan
        \_ When a ship or boat goes through water that is not deep enough,
           the bottom of the boat, usually the keel, kits the "ground".
           Typically the boat was moving forward at the time of impact
           and a sudden loss of forward speed produces an uncomfortable
           and a sudden loss of forward speed (lurch) produces an uncomfortable
           sensation at the least, and damage at the most. Depends
           if the bottom is sand or rocks. Big difference..
           \_ Thanks. So does subs have sensors to detect these things?
              \_ The run of the mill sonars you'll find on commercial fishboats
                 give a pretty decent image of the bottom of the ocean, and I'm
                 guessing that a nuclear sub would have something way way
                 better imaging in all directions, not just along the axis
                 of travel of the boat.  Something or someone fucked up, and
                 I'm guessing the real story will not be reported in the news.
        \_ How funny. I thought the same thing when I read the same news article.
              \_ Active sonar maps fairly well.  Subs are often trying to run
                 silent, and active sonar defeats that.  They rely on charing
                 done by surface ships.
                 \_ In sufficiently deep waters there's a certain depth at
                    which sound speed stops decreasing with depth (because of
                    colder water)  and starts increasing (because of increasing
                    pressure).  If you put your sub on the bottom side of this
                    depth it impedes the ability of surface ships to detect you
                    because the change in sound speeds reflects some of your
                    sounds back down.  If you have a ship running silent (with
                    their depth-on-keel gague off) and trying to keep under
                    this fixed depth, you could have a problem if the water is
                    not too deep and there's a charting error.  So... what you
           \_ This is a lot of congecture based largely on Clancy novels
              and watching Hunt for Red October, but I think the difference
              between fishing boat sonar and nuclear sub sonar is that
              fishing boats use active sonar and subs try to stay hidden
              and use passive sonar. With passive sonar, you would rely
              mostly on accurate sea floor maps for navigation. If mis-
              calculate speed, heading, or time then you could be off course
              enough to hit things you are trying to avoid in tight spaces.
              I'm not sure they still use innertial navigation. It definitely
              seems plausible. -saarp
              \_ I believe they use high freq sonar for getting through
                 icy regions without giving themselves away.  Perhaps
                 there's something similar they use for keel depth?
        \_ How funny. I thought the same thing when I read the same news
           \_ what news is this?  -- sodan who get all news from the motd
                \_ I read it on the front page of cnn yesterday.
           \_ Is it something about the South Asia earthquake reshaping seabeds
              because it elevated seafloors and the tsunami moved around ships
              that sank decades ago?
              \- New motto of US submarine fleet: Run silent, Run agound.
                 How did a sailor get killed? ... flung into something by
                 sudden deacceleration?
2021/06/19 [General] UID:1000 Activity:popular

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