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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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