The best weapon I have used underground was a 15ft canadian canoe with a 4hp outboard on it. We went into a not-very-well-known canal tunnel "somewhere in England" (and people got very upset when I put a pic up). It was awesome and there were workings off the tunnel.
I don't think water and mine exploring are good chums. I remember a time I decided to investigate Wheal Prudence near cligga. I was going to do it properly and take my time and took my stand up surfboard as a precaution against the tide. I used to be quite a hard-core surfer...anyway, I had my short legs-long-arms wetsuit under my boilersuit, rope pack on my back with rope, geological pick and a camera in a daren drum.....oh, and wellies. The surf was about belly button high and about chest high on the sets. It wasn't anything to get excited about. I came out of one of the adits having been quite some time to be greeted with the tide having come in a fair bit.. The bay is like a big cresent and I had the choice of boulder hopping and then a bit of a paddle, or just sodding it and setting off across the bay on my board.
I noticed some people on the cliff pointing as I was quite clearly wearing a head torch/helmet and camo overalls, anyway, I chuckled to myself and carried on paddling. I got about halfway across the bay, looked out to sea and the horizon looked a bit further up than it was, I was quite familiar with this and thought "Set???" Sure enough, the horizon started jacking up and I thought "SH!T!!!" There was a bloody great big wave coming through and concern turned to alarm, I started digging in and paddling for the horizon....I was in no place to get a wave in, or catch a wave, I had to be outside it. I'm not joking when I say that I stroked over the top of a smoking wave whcih was well overhead and the one behind started to break, I did a duck dive (which was quite an odd whack in a helmet) and realised that I was quite badly in the poo. My overalls were soaked, my wellies were full and it was pretty hard going. I sat out the back for a while and another set came though. A new swell had hit.....It was also tubing onto the rocks (breaking extremely hard)
Would I take my chances and try and paddle in to the rocky beach at Cligga in a lull....or try and paddle to St Agnes or Perranporth?
It was bloody hard going and somehow I managed to climb up a rocky point just as a huge wave exploded on the rocks behind me.
Needless to say, I learned some important lessons that day.