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Re: [PSUBS-MAILIST] Once again



You have to also take into consideration that I build Robotic underwater vehicles. so I have a slightly different safety outlook. But towing things underwater is pretty common here in florida, you can't dive without a dive flag (also known as a Jetski target). Every diver or DM drags one behind them. It's just what is.
 
Also the idea is the buoy wouldn't be "Towed" so much as the submersible would stop and take a reading at depth and then continue on it's course. I just don't want to have to surface the vehicle to get a fix.
 
as to the KISS, this is VERY keep it simple. It's one simple mechanical function of releasing a buoy, taking a reading letting the onboard computer do a calculation and then retrieving the buoy and letting the vehicle adjust it's course from there.
 
George H. Slaterpryce III
www.captovis.com
----- Original Message -----
Sent: Friday, April 07, 2006 9:29 PM
Subject: RE: [PSUBS-MAILIST] Once again

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

 


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Stephen Pearce
Sent: Friday, April 07, 2006 8:36 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Once again

 

George

 

I believe with the EPIRB system they can track the course of the buoy by Satellite. What about an Epurb buoy that is released that has an electronic compass that records its course on assent and a GPS that records a reading as soon as it gets a signal and a depth metre that records its depth when released. If the sub is really Hi Tec it could also record the subs position according to its Gyro or other nav system.

 

Surely with the Subs depth, GPS providing the Co-ordinates where the buoy surfaced and its drift path, direction taken to the surface, the subs nav records (and make this downloadable from a solid state memory card) that should narrow its position down.

 

I have not thought through the practical aspects but it sounds do-able

 

Regards

 

Steve P

 

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of George Slaterpryce
Sent: Saturday, 8 April 2006 6:38 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Once again

 

I'm trying to eliminate the error (or at least offset it a little bit) by drawing a circle in the diameter of the extra line let out and then finding the coords in the middle of the circle.

 

Still at no time with the degree of error be any greater than the length of the teather + the degree of error that an GPS system has. I think with the extra step I take I could at least narrow it down by half.

 

George Slaterpryce

----- Original Message -----

From: Nomdae Plume

Sent: Friday, April 07, 2006 3:42 PM

Subject: RE: [PSUBS-MAILIST] Once again

 

George:

My first question regarding this is "how accurate do you need to be?"  I think there's going to be some error regarding the position of your sub verses the position of your float.  For example: drag is going to cause the cable to curve. (Think of the kite-flying anology)  Also, wind is going to move the bouy around... so it might actually be overhead, beside, or ever in front of your sub.

I'm personally planning on going with the GPS-on-surface/IGS-submerged route.  I'll be watching this thread to see what other folks post.

Take care,

NP


From:  "George Slaterpryce" <gslaterp@hotmail.com>
Reply-To:  personal_submersibles@psubs.org
To:  "PSUBS Mailing List" <personal_submersibles@psubs.org>
Subject:  [PSUBS-MAILIST] Once again
Date:  Fri, 7 Apr 2006 13:18:22 -0400
>Once again I come unto you the great PSubbers community with my
>Thoughts, Musings and questions. Ye, Verilly... or something.
>
>First thought, Problem, location underwater. How to ascertain the
>exact (or as near as exact) location of an object under water such
>as a sub. Problem is I don't know how deep you can reliabley get a
>GPS signal. So I thought of this solution that may not be the most
>elegant but I think it would get the job done pretty well.
>
>GPS Bouy on a teather released form depth to the surface.
>You know the depth to the surface, so whatever line you released
>over the depth would be your varience. From there you could get the
>GPS location, calculate two more points on a circle path, then find
>the center point of that, which would give you your GPS location.
>(Illustration below)
>
>(or if you can't see them)
>http://www.captovis.com/marine/designsketches/uwloco.png and
>http://www.captovis.com/marine/designsketches/uwloco2.png
>
>Seem like a good idea to anybody else? comments? Detractions?
>Improvements?
>
>George Slaterpryce
>
>
>
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