Uncontrolled ascent

I have made more than one or two uncontrolled ascents and there are times when I think I have sorted that issue and then lo and behold I do it again

I was doing the first of a night dive course a few days ago.
This was in a quarry and the temp was 14deg.
My buddy reckoned I needed a bit more weight to get down easier.
Quite a few of the divers were in dry suits but I had on a 7mm wetsuit and a corewarmer.

Everything was fine but I seemed to need a bit of air in my jacket when down at 17.5 metres.

First question.
Should I have had no air in then?

As I was probably not paying enough attention to my dive computer, I was unaware that we were getting a little shallower.

And before I realised it, I was ascending without any seeming control.

I tried to let the remaining air out of my jacket but it was too late and I arrived at the surface :depressed:


My buddy had put up her hand to me but unfortunately she came with me instead of me staying with her......even worse!

Any tips to help me would be appreciated.

a) What should I be doing to prevent this?

b) If I start one of these ascents can I stop it progressing?


Thank you for your patience with a rather rambling post.

You only need as much air as needed. Sounds like you put waaayy too much in. Just a squirt will usually do.

a) put less air into your BC when you inflate it

b) yes, but you need to be fast about it. The dump valves dumps faster than you inflator hose does, provided its the highest part of your bc (which the shoulder dump probably would be)

I find that it is much easier to fine tune your buoyancy if you orally inflate, using the power inflate is just too hard to get a precise amount of air.

Not to mention that you are not using good air from your tank .... I know it isnt much, but every bit helps if there is an emergency.

It's expected for you to have to put some air in your BCD to compensate for neoprene compression at depth.

The topic of uncontrolled ascents comes up very frequently on SB. Read this thread. Lots of good advice given there.

In training, you were taught to dump air while you are ascending due to the expansion of air in your BCD. It's good to do this in short frequent bursts so that you can ascend in a controlled manner. I will often advise a newer diver to try to become neutrally buoyant at several points along his ascent. This practice should provide the diver a better feel for achieving neutral buoyancy and making a controlled ascent. Give it a try.

I cannot emphasize enough the importance of staying ahead of the expansion of the bubble inside your BCD. Anticipate air expansion and you will minimize the chances of any uncontrolled ascents. Until you can be confident in your buoyancy control, it would be best to stick to relatively shallow dives (good practice anyway for managing buoyancy).

Another thing you can do is figure out whether you are overweighted. If you are overweighted, you will have to carry more air in your BCD at depth to get neutral. Then, upon ascent, you'll have a larger bubble to deal with. If you are properly weighted, you will move through the water more efficiently and likely have better air consumption. The take-home message here is: Do a proper weight check.

In the case of an uncontrolled ascent, you should be attempting to dump air (being familiar with all dump valve locations is key here AND operating one so that it is at the highest point of the BCD in the water column), flaring out horizontally to create more drag, and keeping an open airway to prevent lung overexpansion injuries.

In the scenario you related, your buddy did the correct thing by attempting to slow you down. She should be praised for having good buddy awareness and being near enough to act. Had she already exhausted all of the air inside her BCD? Or did she forget to do that in the heat of the moment? As soon as she got a firm grip on you, she should have been attempting to dump air, too. The last comment I'll make about the incident is that when she was trying to help with your uncontrolled ascent, she should have been considering that having 2 victims is worse than just one. Hopefully, she slowed down both of you so that your ascent rate wasn't too high.

If you are diving a 7mm suit and a core warmer, you have no choice but to be overweighted at depth. As you descend, all that neoprene compresses, and the weight you needed in the first 5 meters is no longer necessary. Of course, you can't get rid of it because you will need it at the end of the dive, so you will have to go through the heart of your dive overweighted.

That means you will have to have a fairly sizable bubble of air while you are diving. As you ascend, that bubble grows, and your neoprene starts to expand as well. Suddenly you are heading for the surface.

Constant buoyancy is one of the advantages of a dry suit. You add air to it as you descend, and you vent air from it as you ascend.

Dux:

...........My buddy reckoned I needed a bit more weight to get down easier..........

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Maybe gave you too much weight.

Dux:

........Everything was fine but I seemed to need a bit of air in my jacket when down at 17.5 metres.
..........

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To compensate for too much weight?



Spend some time adding and subtracting weight until you can just hold your safety stop depth with no air in your BC. Make sure you only have 1/3 of your usual fill pressure in your tank when you do this. Write down what gear config you were diving and the extra weight needed. Start adjusting weight from this amount.

Too much weight means a big bubble in your jacket. Small changes in depth can mean big changes in buoyancy. With a small bubble in your jacket, the same depth changes make a much smaller change in your buoyancy.

Many thanks to you all for replying.

I have looked at the thread as well that Bubbletrubble linked.

To lowviz..... I did feel as if I was compensating for too much weight.

Tigerman thank you for that tip, as I tend to use the inflater hose and it definitely isn't quick enough so I must pull the dump valve instead.

boulderjohn, I feel as if I was overweighted and yet I appreciate that I would need that with the amount of neoprene.

I'm just glad that for the next couple of weeks I won't need the shortie as well.:shocked2:


I am diving again on Wednesday and am trying to keep these tips in my head and hope not to do the same again.

Having said that the whole dive was brilliant and although I won't wander round the house in the dark if I can avoid it, this night dive was so exciting.

Please, turn upside down and kick for the bottom when you start to rise uncontrollably, even as you dump air. Kicking against rising is the quickest help.

highlandfarmwv:

Please, turn upside down and kick for the bottom when you start to rise uncontrollably, even as you dump air. Kicking against rising is the quickest help.

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Thank you for that as my son and I were discussing it and he thought that trying to swim down might work.

I have tried that very poorly and as I have often given up on the idea of halting my ascent, I guess my efforts to stay down have been somewhat half hearted.