Finally got to experience this superb dive during the day. As usually snorkelled out to the arch and then dropped down. Beautifully still and calm. Swam backwards upside down watching the raging waves sloshing and foaming above in total contrast to the clear, calm silence where I was (until my tank crunched into a boulder because I wasn't looking where I was going).
Felt usual light-headedness at 30 m. Descended further swimming along the huge red-tinged triangular lumps of rock. Felt light-headed again, looked at my depth gauge and realised we'd hit 47 m! Signalled to Simon that I wanted to swim down three more metres so that I could say I'd been to 50 metres; and so it was the we landed on the sandy bottom, our gauges reading 50 m. Simon found a large cubical plastic container about 30 cm across. We only spent a couple of minutes at 50 m and within a minute of two were back above 30 m. Spent the rest of the dive gently ascending. Found the arch and swam back to the Inland Sea. Spent over four minutes at 9m and then another five minutes at least at 6 m. I got out Will's portable tables to check our stops (I was borrowing his stab jacket) but our dive was way off. In our defence our computers were clear by the time we got to 6 m before doing any safety stops.
I almost tightened my weight belt at 47 m, but decided not to - if the belt had slipped out of my grasp at that depth I'd have been dead meat. Lesson learned: only tighten your weight belt at the start of a dive when it's not too deep so that if you lose it you won't torpedo to the surface and die.