This Saturday saw us at Wraysbury with a class of 4 students for the Drysuit Specialty course, Duncan OSWI, plus another 4 doing an OW Completion, with an OWSI, another DMT and a recently qualified DM. I did this course myself in 2010. Water temperature 3-4°C, easily the coldest I have dived in (previously that was 9°C at Plymouth last Easter). I was actually fine in my new PBB+ undersuit bought at LIDS, and my neoprene drysuit, apart from that my right wrist seal is leaking, and my head in a 3mm hood was very cold at first. I’ll need to get both of those sorted, urgently, as I am back again next weekend, both days! Also I test-dived the Suunto Cobra I got on eBay for less than half new price. It read my initial tank pressure as 165 bar, which seemed a bit low but was possible, and my gut feel is that it tracked my air consumption correctly (82 bar from a 12L tank used in 24 mins at an average depth of 5.8m gives 25.9L/min SAC which is reasonable considering it was cold and I was swimming constantly). I need to compare it with another gauge, and maybe get it serviced too.

Specific feedback/lessons learned:

• When doing surface support, kit up. For the first dive, I was the surface support, checking divers in and out of the water (times, air, etc), handing in or taking back weight as people buoyancy checked, keeping an eye on divers still on land or who had returned early. Another DMT had told me not to bother getting my drysuit on, but I did find myself up to my ankles in the aformentioned cold water as the pontoon wasn’t in the greatest shape, then had numb feet for the rest of the day!
• Double, triple check kit before leaving the dive centre. We arrived on site with what we thought was 20Kg of spare lead; when we came to dive, there was only 4Kg which got used almost immediately, despite each student supposedly having been issued 10Kg at the centre. Even the belt we threaded it on was taken. I had 12Kg from the centre for myself, which vanished before I could use it (as I was surface support for the first dive, and in on the second) In the end I just rented lead to save hassle, but I shouldn’t have had to put my own hand in my pocket for this. I even had to pay to get into Wraysbury! But the DM(T) has to be responsible for everyone else too. It’s Divemaster as in quartermaster.
• Think about where the students will be, and position accordingly. I think this will just come as I assist on more courses and get a feel for the flow of things. It’s important to be able to see everything, to be in a position to react quickly, and yet be out of the way. This means thinking one step ahead of where the instructor has put the students and what he is doing with them.

Every diver knows how to do a buoyancy check, and every diver knows that if you are overweighted, buoyancy control is a lot harder, since the air you add to be neutral at a given depth changes volume as you ascend and descend†. The really experienced divers with us, the instructors and experienced DM all seemed to be negative enough to hold down a flailing student, yet had great buoyancy control of their own without obviously adjusting their BCDs. I think 10Kg should have been enough weight for me in that kit in freshwater, but I went in with 12Kg for that purpose, yet my own buoyancy was all over the place, or at least it felt that way. How they do that is something that I’m going to have to learn. Another thing to think about is what exactly to do if a student shoots up like a Polaris. On the one hand, we are responsible for them. On the other, in a class like this they are already certified divers and responsible for themselves. Blowing an ascent rate if you only dive once a year is one thing, doing it several times a day, every weekend is bound to take its toll, even if only from 10m, and I want to go on being a healthy diver for a long time!

† When I did the Cavern Specialty in Mexico in January, we learnt one trick cave divers use: 33% of your weight is only needed for descent and to control ascent with depleted tanks, so to ensure perfect neutrality in the confined environment, they simply have some of their weight clipped on, which they leave at the entrance to the cave and pick up on the way out. Why are so many divers overweighted then? Because it makes the descent very easy and they dive a very simple profile that is down, along a reef wall say, then up (and then blow their safety stops!).