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Tomek
27-05-2016, 09:23 PM
I'm getting back into the water after almost 3 yrs break, theoretical knowledge is quite rusty so would appreciate some wisdom.

Practice is even more rusty hence the need for some basic training.
I am planning on doing some buoyancy control drills and need advice on safety.
Exercise example:
- drop to 6m, get comfy/stable, ascend holding 1 min stops at 5,4,3,2,1 m
- if that works, add task loading: SMB, gas sharing, etc
Depending on the scenario the whole thing would take between 7-9 minutes

Finally, the questions:
1. Can I do this repeatedly without getting out of the water from a DCS point of view? If yes, how many times? If there is a limit, how do I figure it out?
2. Can I do it after a longer dive, say 60 min at avg depth 12m? What should be my surface interval?
3. Can I do it before a longer dive, say 60 min at avg depth 12m? What should be my surface interval?
4. How does swapping air for ean32 change the above?

Garf
27-05-2016, 09:47 PM
The way I do this drill is this

1 minute to 3 metres
1 minute to 6 metres
2 minute on the bottom to stabilise, and get ready for the ascent.
1 minute to 5
1 minute to 4
1 minute to 3
1 minute to 2
1 minute to 1
1 minute to the surface

For a total drill time of precisely 10 minutes. I then make the people I am coaching wait 5 minutes, which is long enough to reset everything and have a chat about what they could have done better, before repeating the drill. Now, you're not going to get anyone who will tell you that any repetitive profile is "safe", but I have done this drill 12 times in a day across 3 dives with an hour between dives with students. On practice days with just myself and another GUE diver where I am not responsible for them I have done this all day long. I would definitely use 32%. I might even use something richer. I mean what have you got to lose by just diving with 50% apart from a few quid if you know you are not going to descend to a depth where it will become anything like an issue.

You also need to consider how they go and adjust your plan accordingly. Theoretically you'd be very unlucky to get bent doing this sort of drill all day long, but if you find that on the first two you lose control and pop to the surface from 3, then I would wind back how many ascents you are planning. For example, I once saw someone carted off from NDAC after doing a drill like this at the end on an hour long deeper dive because they messed it up and popped up. So do your deeper longer dive with an ascent that you know you can handle, and save the drills for another dive.

All of the above is my experience and opinion. Obviously you need do your own mental risk assessment and decide where your limits are. I once spent an entire weekend doing 3 metres per minute ascents from 21 metres with GLOC in Vobster, and I really do mean all weekend. Not sure I'd do that now :)

Tomek
27-05-2016, 10:15 PM
Thank you, that is very helpful. Good idea with with a richer mix.

WFO
07-06-2016, 11:09 AM
I would say do not do this repetitively after a longer deeper dive of pretty much any thing, there was tale a while back that shallow ducks while still off gassing were to blame for some "undeserved" dcs hits. Theory was that it compressed bubbles allowing them to pass through the lungs, then they're in arterial circulation and expand again.