Have no experience with the explorer but have plenty with using an 18" coil.
The quick and dirty of it is; if you just have to spend your money and do it
for a 18" coil you better make it a DD and not a mono. It is VERY hard to
pin point with a mono that size unless you turn it up on edge and go across
the target two way's, 90 degs. from each other and on some machines that
can turn into be a pain in the a-- due to the shape of them. The DD will pin
point like a smaller coil and give almost as much depth with out having to
turn it on edge. And now for the big one ( "drum roll please" ) you can leave
your sand scoop at home and drag out your #2 shovel cause your going to
need that sucker to dig those targets that your going to find that are three
feet down! Oh, and did I tell you how heavy a 18"er gets while you try to
swing it with one arm? OK what you going to do with that shovel ? It can be
done and has been done but it sure ain't fun! Me; I try to think outside the
box when I can!