Tom, my main concern would be mineralization from salt water given that manufacturers claim they can locate sources of water, caves etc. My main objective is to identify concentrations of coins and larger objects on beaches. I am not very familiar with a 2-box machine so thank you for the advice.
Many many machines do *just fine* on wet-salt beach minerals. And if you got into some nasty jet-black mineralized sand (rare) just reach for a beach pulse machine. "mineralization" is not-so-insurmountable that only a GPR somehow solves that.
And I don't understand why someone would be looking for water or caves on the beach ?
I can understand "concentrations" of coins, but it would depend on what you mean by "concentrations" . Are we talking chests full ? Are you talking hands-fulls (like where mother nature groups them at bedrock divots?).
GPR's are more the domain of bottle diggers. Who are looking for ground anomolies to tell them where outhouse pits were (for instance). And sure, they'd show large anaologies. But if your definition of "concentrations" was to mean "entire chests", then don't think that the GPR is going to show magical shapes of chests and jars. They don't have that sort of pixel size detail. Instead you just see blurs and blobs.
A 2 box machine will handle wet normal beaches just fine. The depth on a soda can will be up to 2 ft. or so. The depth on a toaster oven will be 4 or 5 ft. The depth on a refrigerator sized objects will be 6 or 7 ft., etc..... So too will many standard machines achieve those depths (and so too will a GPR, etc...). But the benefit of a 2-box unit (like a TM 808), is they DON'T see any object smaller than a soda can . Thus you're not bothered by nuisance individual coins. And is only going for metal (not "voids" or "caves" or "water" or whatever you're saying the GPR claims).
If your "concentrations" are scattered "patches", then no, the 2-box won't work. They have to be assembled into one unit. Like a jar, box, chest, or whatever. Not sure how a GPR works for "scattered" but I betcha that's not going to get anything smaller than big box either.
