Google 'bathymetry charts' in any region of the planet and you may find 'free' bathymetry views. Today, for our commercial and military purposes, the entire world's oceans are accurately mapped and surprisingly close to the sim for gaming purposes.
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http://en.wikipedia.org/wiki/Bathymetry
Also, I read my fathometer de riguer. The only pinging that might alert warships is foward looking sonar. That signal strength out and return is to be avoided when warships are in the range to listen!
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DID, no cheats, no shortcuts, no non-historic equipment deviations. Boat and crew safety is integral with my immersion style! Follow the historic events during your patrol:
http://www.uboat.net/today.html