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Re: [PSUBS-MAILIST] Once again
Jay - how do the specifications of the $300 sensor you were looking at
compare to the Microstrain 3DM-GX1? Also, can an off-the-shelf sonar be
used to provide speed-over-ground?
-Sean
Jay K. Jeffries wrote:
Gentleman,
Let’s get a grasp on reality here, it is obvious that many here
haven’t spent a whole lot of time underwater whether scuba diving or
in a submarine or submersible.
1. You don’t want to tow anything in a sub, the line will either get
tangled in something else or foul the sub which can ruin your whole
day. That is why the CSS Hunley stopped towing the explosive mine and
had it put on a pole in front of the submersible. The SEAL’s wet sub
probably has a GPS that it can spool to the surface and quickly
recover in shallow water to get a fix on a long run (there was a call
for proposals for something similar to this over 10 years ago).
2. Where a submersible is operating will be pretty barren (as is most
of the ocean) and will be over a small scale area so bathymetric
navigation is not practical (high-resolution bathymetric charts were
classified previously so our previous enemies couldn’t use them to
hide in small gullies off of our coasts).
3. The Navy spent millions on the DSRV’s inertial guidance systems and
never supposedly got it right. MIT’s Draper Lab spent an inordinate
amount of time trying to resolve the issue. A small 6-degrees of
freedom (3 gyros and 3 accelerometers) sensor package is now available
at a fair price (~$300 when I looked a few days ago for another
issue), anything less will not supply enough data. This then has to be
integrated into a navigation system (wait until you see the math) but
you will find that the system drift will be to large for the type of
navigation that you are seeking.
4. In the near shore (littoral) environment, bottom currents can vary
erratically and change quickly due to changing tides, river outlets,
and changing water densities. Thus dead reckoning accuracy should be
called into question.
5. Most research and commercial subs navigate via scanning/side-scan
sonar and/or triangulation by surveyed sonic buoys.
6. When you read accounts of research/commercial subs without acoustic
triangulation or scanning sonar, you will find that searches for a
target are hit or miss. Most often miss as visibility generally isn’t
that great so you could pass close right by your target and never know it.
KISS is the guiding principal in all things submersible, complicated
solutions will just get you into trouble. Size and power requirements
are also an issue, other than the /Euronaut/ you are jammed into a
small tube or ball with minimal battery reserves. Probably the most
economical solution is acoustic triangulation.
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
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