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Where do subs measure depth from?

Discussion in 'Non-Diving Related Stuff' started by Raywerner, Jun 7, 2003.

  1. Raywerner

    Raywerner Angel Fish

    I have been watching a spate of submarine-related shows on the Discovery Channel and PBS, and I was wondering this: When the Captian says "Take 'er down to 150 feet." where are they measuring the depth from?

  2. trymixdiver

    trymixdiver Manta Ray

    good question, im a sub fan and i never thought about it before.

    I would assume depth is measured to the bottom of the keel.

    If the water depth is 200' and your ordered to take her down to 200' measuring from some where above the keel your going to hit the bottom. Why make it complicated by having to mentally think " we are going to 200 ' but our boat is not measured from the bottom of the keel, how many feet are added to the depth reading to give me the boats actual depth at the lowest point of the keel".

    then again dont we pay $600 for a toilet on a sub ? If we are dumb enough to spend that much on a toilet seat maybe we are measureing from some other point. :)

  3. Dr Deco

    Dr Deco Medical Moderator Staff Member

    # of Dives: I just don't log dives
    Location: Issaquah [20 miles east of Seattle], Washington.
    When I watch films concerning submarines, and depth gauge is shown, the gauge plate will always indicate “Depth beneath the keel.”

    Dr Deco
  4. Grajan

    Grajan Manta Ray

    My guess is a sub commander is MUCH more worried about the threat above him than below.

    I would expect the datum would be the top of the periscope. There are plenty of people (such as the navigator) to worry about where the bottom is and they usually operate in ocean depths anyway.

    There must be a subbie out there somewhere to make fools of us all.....
  5. Doppler

    Doppler Dive Equipment Manufacturer

    Maximum depth is read at the keel (lowest point of the ship.... and everyone knows when the keel is deep enough to submerge the tower.

    Watch Hunt for Red October!

  6. canuckdiver

    canuckdiver Solo Diver

    datum on depth is measured from the deepest point of the keel.

    Usually, this is the skeg in front of the rudder. If you look at a picture of a sub at dock, you will see on the aft quarter, a line of depth markings similar to what you would see on the hull of a frieghter.
  7. donacheson

    donacheson Solo Diver

    # of Dives:
    Location: Maryland
    Taken literally, it makes no sense - for how can a sub detect the bottom in the deep ocean?

    Pickniness aside, I think I've seen the same, or similar wording, and taken it to mean the pressure depth at the keel.
  8. Goeduck

    Goeduck Nassau Grouper

    Seeing as how most of the oceans have been charted, and since all submarines have charts, I don't think that submarine skippers worry too much about the bottom in the deep ocean. They are more worried about "shallow" depths, and if they need to know exactly how far off the bottom they are, they can use sonar.

    But for most of their navigating in the "shallows", they use their charts.

    They are also worried about uncharted pinnacles that come up from the ocean floor that they might run into, but again, I think that most underwater "obstructions" are also located on the charts.

    I also believe that all their depth readings are taken from the lowest point of their keel.

    I am no submariner, nor am I pretending to be one, but I do a lot of reading.
  9. jepuskar

    jepuskar Instructor, Scuba

    # of Dives: 500 - 999
    Location: Chicago, IL
    Maybe Raywerner means 'where are they taking the depth reading from'...meaning, how do they know they are at a specific depth. Meaning, where is the pressure transducer located at.....on the keel somewhere? Physically where does it get its reading from?

  10. gkwaldee

    gkwaldee Angel Fish

    Actually, most have it correct. THe depth is measured from the keel, however, there are a number of points along the keel where these "depth sensors" are. Yes, theyre called depth sensors. So, depending on what angle is on the boat, the sensors will have varied readings.

    The sensors work by reading sea pressure, then converting it to feet. There are two types of depth gauges, shallow and deep. Its important to secure the shallow depth gauge at a certain depth to keep from over pressurizing the system.

    The way that a submarine, or any other vessel, reads the ocean floor depth is by a fathometer. This device sends a sound pulse to the bottom and calculates the time it takes to bounce back to the boat and converts it to feet or fathoms.

    There are any number of things that are "more important" than another depending on the situation at hand. You can imagine that most times the bottom of the ocean is very important because its many 100's of fathoms deep. And normally we dont want to hit the bottom, especially when its 12,000 feet down!!

    Hope that helped

    tiny bubbles

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