The other coil that acts up is a 10.5 inch round, same part number as the good one. I got it used and almost as soon as I got out into the water with it the first time I wasn't paying enough attention to the waves and got knocked over. Figured I stepped on the first 10.5 inch and affected the coil, but now I'm not so sure it wasn't that way when I got it.
Depth is a little hard to tell in the really wet sand where I mostly use the Sand Shark ... but I have had to dig more than one scoop at times to get a target I was real sure I was right over with the first scoop. Scoop gets down about 9 inches, so ... I'd guess conservatively it is good for a good 10 to 12 inches on coins and maybe a little more.
So far I have only pulled junk rings with the Sand Shark. Guess I haven't put the coil over a good one yet. I'm on the third set of batteries in it. So I probably only have between 30 and 40 hunting hours with it so far.
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