One other point: You can't use GPS underwater (GPS requires multiple reception of UHF signals from several satellites.)
So, underwater, you're still using essentially dead-reckoning from speed and course assumed from the instruments. Yes, those instruiments are good, much better than the iron compass and gyros and pitlog (submerged speed sensor) of old, but it's just more accurate dead reckoning.
If the mountain underwater wasn't on the chart -> there's no way you're goign to be able to plot a course around it, and (if it's slope underwater is steep enough) there's no way you're going to spot it in time even IF the fathometer was pinging.
Which, in deep ocean transits at high speed, is normally off.
So, underwater, you're still using essentially dead-reckoning from speed and course assumed from the instruments. Yes, those instruiments are good, much better than the iron compass and gyros and pitlog (submerged speed sensor) of old, but it's just more accurate dead reckoning.
Yep. We'd come up to PD, catch a couple of satellites and reset the DRAI (dead-reckoning analyzer indicator ?) and boogie on.
... even IF the fathometer was pinging.
Which, in deep ocean transits at high speed, is normally off.
Procedure on the Tinosa was to send a watchstander out to get a sounding every couple of hours or so.
"Piss, Fetch (coffee), Sounding." was the order (I doubt you'll find it in the Bluejacket manual).