Last saw this in use to work on the lock gates at Junction Lock, I think, when it was refurbished. They lower the entire thing into the water in a corner of the harbourside, making a roughly watertight seal along the muddy bottom and the harbour walss, and run a pump to suck/keep the water out of it, leaving a little dry corner that someone can work in without needing a drysuit or similar. And, you know, actually being able to see what they're doing.
GPS Coordinates:
51.44821, -2.62260
Location: Spike Island
