Fresh Water Search - 10-20 Of Silt - Best Option?

[ff404]

Fresh Water Search - 10-20' Of Silt - Best Option?

Just doing some research. Looking at a potential site, fresh water. Fairly small area. There is the possibility of anywhere from 0 to 20' of silt, unknown consistency. I understand that side scan technology will not help if items are not on the surface. I've looked at the stuff Fishers offers as accessories for the Pulse 8x, but seems like the best penetration they have is 8 feet. Are there any other better options for metal detecting (non-ferrous) this site? The water depth is unknown at this time.

Yes, lots of unknowns, but of course that is why its the research stage.

Anyone have any recommendations? Information, prices, etc. Thanks in advance!

 

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[pcolaboy]

Re: Fresh Water Search - 10-20' Of Silt - Best Option?

Google "Sub-bottom profiler" I believe that may get you what you need but you'll need some pretty hefty pockets. Another thing to consider is a good multi-frequency fish finder. A friend of mine has a newer Lowrance multi-frequency sonar that is very good at detecting and showing changes in bottom density as much as 8-10 feet below the top layer. However, most of his deep accurate readings were in water less than 50' of saltwater. A couple of years ago he located an aircraft fuselage that was 9 feet below an upper layer of silt in 32' of saltwater using this method.

Good luck,

Pcola

 

[rssharpetx]

Re: Fresh Water Search - 10-20' Of Silt - Best Option?

Sub-bottom is a good approach but shallow water sub-bottom is not so simple. Most people use chirp sonar and this tends to have longer out going pulses thus your transmit signal is still going out and wipes out first part of receive signal or area of interest in shallow water. I am NOT trying to sell anything just trying to show some examples. We developed sub-bottom systems just for this type application. see sediment mapping www.specialtydevices.com. Another real good approach is resistivity. It is very similar to ground penetrating radar except done on water towing a small array. There is a company in Austin Tx that has a good unit. If you cant google let me know and I will forward info. I cant recall company name (not enough coffee yet) After all this the simple question should have been what water depth are you working in?

regards

 

[Darren in NC]

Re: Fresh Water Search - 10-20' Of Silt - Best Option?

I would listen to Scott's recommendation above - he's one of the experts in this area. Also, depending on the consistency of the silt, a side scan (or Hummingbird) may still work...

http://forum.treasurenet.com/index.php?topic=214951.0

 

[ff404]

Re: Fresh Water Search - 10-20' Of Silt - Best Option?

Thanks for the help so far fellas. As stated in the original post, this is still in the early, early, early research phase. The area is in the states, and I'm currently in Africa, where I will be for at least the next 9 months, probably more like the next 21 months. So plenty of time to do lots of research on some different areas I suppose.

As far as water depth, still working on that. It is my intention to purchase one of the Humminbird units whenever I get home, if, they will work out of a RIB or smaller inflatable boat. Does anyone know if there is any reason why the system wouldn't? The idea behind the inflatable boat is ultimately mobility and ease of transport to different sites. Obviously I understand that I will have to fabricate up a mounting system, but that won't be a problem.

Thanks very much for the great information, please keep it coming!

Matt

 

[rgecy]

Re: Fresh Water Search - 10-20' Of Silt - Best Option?

Find an old Lowrance paper chart recorder that uses a 20khz or 50khz transducer. This will work OK for a crude sub-bottom profiler and you have a hard copy for recording. You can also find some older lowrance lcd units that record. The lower the khz, the deeper it will penetrate. Now, thats not going to tell you if you have non-ferrous metals or not, but it will show you if you have some objects burried in the silt.

As for detecting non-ferrous, depending on the size of your target, you could take a two step approach and use a PI metal detector with a large 1m coil and a Magnetometer. If you get a reading with the MD and no reading with the mag, it is most likely a non-ferrous metal! Start digging!

If the bottom is fairly smooth, you could build a sled for both and tow the mag behind the 1m coil.

Good Luck,

Robert