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Fairlane66

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 #1 
I currently use a Garrett GTA-500  metal detector for wreckchasing.  While it works well, I've been less than impressed with the target detection depth I get....generally about 6-8 inches, but little more.  I was wondering what other brands/models you wreckchasers use and what your results have been.  Anyone have any recommendations for a Garrett coil that'll provide better depth detection than the stock coil this machine came with?  Also, have any of you had experience with metal detectors that provide good metal discrimination.  My Garrett tends to show almost everything at a crash site as either gold or some sort of coin.  As you might well guess, the gold or coin hits tend to be nothing more than twisted aluminum.  Thanks. 
DaveTrojan

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 #2 
That is the main problem with using any metal dectector at a crash site. There is just too much metal around and the detector goes crazy. The detectors are set up to find metal and can't descriminate between the different kinds very well. They are best used in the forest where you don't know exactly where the site is to help locate the highest concentration of parts. I've used them with success this way several times.
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SixbyFire

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 #3 
I've got a Bounty Hunter metal detector, Tracker IV model, and it's got three tones, high, low, and broken, to tell you what kind of metal you're detecting. Aluminum, usually a "junk" metal for metal detector people gives off the broken tone. This is how my son and I recently found a crash site. The other tones, high and low, along with the broken tone are really accurate in what you end up finding. The metal detector was invaluable for the site we found since some of the features in the crash photos changed over time, and while digging wasn't allowed, we found enough on the surface to confirm the site.

I bought the detector for about $100 on Amazon.com, and also bought a 4" coil which is supposed to be more sensitive, but the 4" coil is solid, without a hole in the center, and it's just easier for me and my son to see where the main part of the tone goes off when you can see through the coil, instead of not doing so with the 4" one. Maybe if we were going to dig up big holes, the 4" coil would work great, but for our searches the larger coil did the trick. The metal detector has quite a few settings that take practice to get used too, and you can search using all metal mode, which is more sensitive, or use the tone discrimination mode, you can even filter out the aluminum stuff too, but that's not really useful for what we were searching for.

Jeff
unimogbert

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 #4 
Garrett makes alternative size coils for most of their detectors. Larger coil generally means deeper depth but you may lose the really small targets (like small rivet heads which might be a good thing). Larger coil is heavier and may change the balance of the system.

The calibration points on the detector are for assumed coin/jewelry hunting so the target ID is totally irrelevant for working a wreck site.  Even working parks for coins I've found that flattened aluminum pop cans (stomped on vertically) read high conductivity and show to be quarters. (sod layers drink pop and hide the evidence under the sod mats as they lay them in City parks)

Working the Colo Springs B-24 site where we are mapping and picking up the parts for the City I've found wide variation on soil conditions which affects depth.  Best depth is damp soil after rain. Otherwise that particular soil has lots of minerals that mask detection so we're only getting a few inches of depth for  palm-sized scraps.

Some of this can also be technique. The detection zone under the coil is kind of a cone shaped. The deepest depth of detection occurs at the point of the cone. This suggests that highly overlapped sweeps will reach more of the deeper area than  non-overlapped sweeps.  For complete coverage it's best to do heavily overlapped sweeps of the area from several different directions. (Obviously this is very time consuming.) Putting the coil as close to the ground as possible including brushing the dirt lightly in flat areas(that's why they sell coil skid plates) will yield deepest depth. Detecting over broken stone is tough because the parts are down in the cracks where the detector coil can't go.

For deep detection of large objects (large only) (http://www.garrett.com/hobby/hbby_gti2500_depth_multiplier_package.htm) the depth multiplier could help. It won't detect small stuff (coin sized) but will reach quite deeply.
I did a survey of the B-24 area with one of those hoping to find engine or landing gear below the surface. I DID find two areas of interest which turned out to be where engines& gasoline burned and left a wide charred layer about 4" below the surface that was conductive.


I'm currently using a Garrett ACE 250. It's a great detector. Light, powerful, very economical on batteries. It's far better than my Garrett ADS-7 from 1985 which cost 3x as much and uses 9V batteries more quickly than the Ace uses AAs. I have the depth multiplier attachment for the older detector.

Garrett sells books about detectors and detecting which explain lots of this stuff. It might be useful to read more about the capabilities and limitations of the tools. Like so many other things I see on TV, when I see someone using a detector on a TV show I laugh at how totally incorrectly they are being used.


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Unimogbert
huron1988

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 #5 

What Dave said is how I have used my Bounty Hunter model. I have never found the depth indicator any help or accurate. The "instructions" that came with it are maybe a page long and not very helpful. For wreckchasing purposes it works fine at finding any metal. If I was a newbie "treasure hunter" I'd be wasting too much time on pop tabs and such and I'd be angered with the lack instruction.


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Jeff Benya
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unimogbert

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 #6 
If you're working a city park then the metal typing is more effective because you are just detecting coin sized or similar objects which the detector is calibrated for. My Garretts are pretty good at telling one coin type from another though they aren't perfect.

But for wreckchasing that's immaterial. I have yet to use a detector looking for a crash site where interference from pop tabs and bottlecaps is an issue.

I've not needed to  use detectors when looking in the mountains.

But out on the plains where wrecks got picked up they have proven really useful because the debris left is so small or is buried a few inches.
I've detected small rivet heads, broken instrument case screws. Things the size of pellet gun pellets.


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Unimogbert
simongirty

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 #7 
Most detectors even the cheaper ones have an "all-metal" setting which when selected they will detect all metal ferrous and non-ferrous, they also may have a "pin point" option which is basically an "all-metal" setting which you can quickly switch of and on by pushing or holding down a button. Either of these options will detect metal at much deeper depths than the setting designed to discriminate whats usually thought of as "trash". When looking for a wreak site I would think there would be less of a need to discriminate out the trash due to many time they are in a remote location and any areas where there is a dense concentration of hits could indicate a crash site. I would think a $300 MDer would work almost as well as a $1500 one for what you are using them for. I have a Garret Ace 250 which can be bought for about $220 and I have detected large ferrous objects up to 14 inches deep on pin point. This is pretty common for detectors in this price range when set on "all metal" mode.
Dennis

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 #8 

When you are hunting for a micro site in an area with 60+ years of mulch and compost, the metal detector is invaluable.  It also came in very handy for determining the boundaries of the debris field. It also comes in handy when hunting in shallow, murky water (if you have the waterproof type).  Dennis 

kittyyang

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 #9 
Among all the detecting activities, gold metal detecting is the most interesting one. It can not only relax both your body and mind , but also give you a big fortune if you are lucky enough.Next time if you feel bored, you can pick up a gold detector and have a try.
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