I wouldn't mind the diving, but I'm not too keen on 6-7 hours of decompression...
I unwittingly raced a smaller boring machine once--not underwater. I was working for a Navy contractor who was competing with another Navy contractor on a water main project for the base.
There was one long run under a building, and one short run. The bigger contractor brought in a boring machine for the bigger job. My company dug a hole on either side of the building, stuck a large diameter piece of pipe in the hole on one end, then put a hydraulic jack and timber against it. My job was to crawl in the pipe to dig, hammer, and move dirt. I would come out and adjust the jack every 6" to a foot. Some of the rocks were nearly the diameter of the pipe so it took quite a bit of air hammer chiseling to fragment them. The hardest part was getting the dirt out...I finally found it most efficient to scoot a few shovels full at a time by wedging my body against it and sliding.
What I didn't know until near the end is that there was a case of Moosehead beer bet by the superintendents about who would get through first. We won easily (I went about twice as fast linearly as the big borers in the article.) Not only did I dig faster, but the borer broke down halfway through the job and wasn't repaired by the time I finished.