Fast Ascent

[TSandM]

Well, the key to the weight problem is to do a proper weight check. Trying to diagnose buoyancy problems by adding and subtracting weight at random is rarely successful. After that, what supergaijin said is spot on:

It's a fairly common problem and unfortunately our human responses often contribute to it. When divers start ascending unintentionally, often the first response is to try to deflate the​

BCD

, then realise that their body position doesn't allow air to escape, wriggle around getting the hips forward (which often involves small movements of the fins propelling them upwards), and taking a big breath in as some anxiety sets in. Especially in shallow water, it only takes a few seconds to be at the surface.​

For me, the key was breath control. Since I had problems holding shallow stops, I learned to worry about them, and the minute I felt the slightest bit out of control, my breathing would change, and up I'd go. Doc Intrepid (a wonderful SB member who sadly no longer posts here) told me that buoyancy was 80% mental, and he was entirely right. Once you can remain completely relaxed during ascent, then if you get a bit buoyant, you'll just exhale and vent and everything will be fine.

The final piece of the puzzle is to know that there is a window in depth that you can control with your breath, and that window is smaller and smaller as you approach the surface. By "window", I'm referring to the amount of expansion in the BC that you can compensate for by exhaling. You HAVE to recognize that you are rising before you have left that window, or exhaling won't stop you. Jonnythan here on SB told me to organize my ascents this way: Inhale and begin to rise, then EXHALE; if you stop, fine, but if you don't, VENT. That really helped me.

If your BC is truly empty and you cannot stay underwater, you are too light, but looking at the weight you're carrying, unless you are a very large person or using a brand new wetsuit, I suspect you have enough weight. But as I said at the beginning, only a formal weight check will tell you for sure.

 

[bolts]

The dive was on a wreck, which was more like a big hollow rowboat, so to get from out of the interior, you had to ascend up and over the hull sides. This made for some good practice to ascend and decend from say, 20' to about 5'-10' and back down again. I did this a few times, without too much difficulty, and like was mentioned previously, breathing control is key. It was just near the end that caught me out. Really frustrating. I am a fairly large guy, so taking a full lungful of air makes a big difference.

Thanks for the pointers everyone, definitely points to consider.

I haven't done a bouyancy check with this new bcd after a dive, but did one last year with practically the same gear (same exposure protection, rental regs/bcd), and was pretty close to the ideal weighting with 24lbs and empty tanks. I'll have to do some more checks in future dives for sure.

 

[electrix]

It is very common for new divers to be cruising along at 20' at the end of a dive when their AL80 tank gets low and the next thing they know they are on the surface, in my experience it is unusual if they don't end up on the surface and can't get back down.

 

[supergaijin]

That is pretty much the litmus test for appropriate weighting. Try to get down with an empty tank and empty BCD on breathing control alone. The PADI description of proper weighting blows IMO. There are too many factors for the 'float at eye-level holding a normal breath and then add 1 or 2 kg to offset the weight of spent air. Looks good in a swimming pool but.

Saying that- I regularly add a kg for diving in strong current or in other situations where my breathing rythmn is likely to change.

 

[boulderjohn]

When I work with new students, one of the points I keep impressing on them is that air always wants to go up. When it goes up to the highest point of your BCD and has no escape route, it will stay there. If your body changes position so that a different point in the BCD is higher, it will go to that new place. When you are reasonably well weighted and near the end of the dive, you should have a relatively small bubble moving around in the BCD, always looking for the highest point.

That simple concept takes a while to sink in. If the highest point in the BCD does not have a vent, that air won't come out.

If you are using one of the more common models of BCD, you will have 3-4 different places that air can leave the BCD, and IMO the inflator hose is the least convenient. I only have 2 such places, and I still rarely use the inflator hose. When I am getting near the end of the dive and don't have much of a bubble, I sometimes have to give some thought as to where that bubble is and then move my body to make sure it gets to the right place for dumping.

Sometime when you are under the right conditions for messing around (like a pool or other benign environment), get yourself into a situation where you only have a smll amount of air in the BCD and then put your body through a series of spirals and other gymnastic maneuvers. Pay attention to how the bubble moves in the BCD. Play around with getting the air to come out of each of the different dump mechanisms in the BCD.

 

[dpaustex]

I'd say work on properly weighting, before your dive. But I think you hit the nail on the head with your position, "head up/tail down", and you did indeed act like a wing. Any current in this situation is going to send you up, like a sail.

Kudos to you for realizing the problem, and asking for a potential fix.

Might caution against high-current diving with being new. Work on nailing your buoyancy in calmer waters, first, would be my suggestion.

 

[freewillie]

The dive was on a wreck, which was more like a big hollow rowboat, so to get from out of the interior, you had to ascend up and over the hull sides. This made for some good practice to ascend and decend from say, 20' to about 5'-10' and back down again. I did this a few times, without too much difficulty, and like was mentioned previously, breathing control is key. It was just near the end that caught me out. Really frustrating. I am a fairly large guy, so taking a full lungful of air makes a big difference.

Thanks for the pointers everyone, definitely points to consider.

I haven't done a bouyancy check with this new bcd after a dive, but did one last year with practically the same gear (same exposure protection, rental regs/bcd), and was pretty close to the ideal weighting with 24lbs and empty tanks. I'll have to do some more checks in future dives for sure.

BC's have something referred to as inherent buoyancy. That is the natural tendency of the BC to float when fully empty. It varies by brand and if included in the scuba gear reviews something I like to know about. Generally, the more the inherent buoyancy the more the BC will float. That generally means that you will have to add extra weight just to offset the BC itself.

I have this problem with my daughter since we rent her scuba gear since she is still growing. We ball park the weight from the last dive but nowadays I'm in the habit of diving a few lbs heavier just in case she needs extra I can had it over to her without calling the dive or having to head back to the boat. I know a formal weight check would be better but sometimes we don't have an opportunity before a dive.

Since this is your own gear you should definitely do a formal buoyancy check and then adjust from there. I also had a problem when I first started with floating up unintentionally. As you ascend the air in your BC will expand as well and then create more buoyancy and lift. This is effect is even greater at shallower depths. These days I'm in the habit of fully venting my BC before I start my ascent then using my breathing for buoyancy control and kicking to the surface. During my training we were discouraged from using our BC's to ascend. My instructor kept telling us, "no elevators to the surface."

 

[bullfroger]

New divers can have a tendancy to keep their lungs over expanded because they are not relaxed. I took a guy out once who showed me he was properly weighted by sinking at the surface when he exhaled. So we decend from the surface to 20 feet. All of a sudden he couldn't stay down. That with out adding any air to his bc. Wet suit compression should have made him negativly boyant. The only explanation could have been he was breathing off the top of his lungs. By that I mean his lungs were fully expanded except for small exhalations. I put rocks in his pockets, but later in the dive he panicked and went screaming for the surface. I made him drag me which slowed him down enough to not embolize.
He never went diving again.

 

[halocline]

If it's a new jacket BC, chances are the only way to make sure ALL the air is out is to get vertical, raise the inflator hose straight up over your head, and vent, maybe even making sure there are no trapped bubbles by holding the vest part down with one hand and stretching the hose up with the other. I've found I had to contort a bit to get every last bit of air out of some jackets....just another reason why I dislike diving with them. But, I'm talking about small amounts of air that really shouldn't send you to the surface unexpectedly.

I'm not sure why water in the BC tells you that all the air is out, to me it just says you opened vents that were not at the highest point and water rushed in, displacing air to a higher spot in the BC. I've seen lots of student divers do just that, and emerge from the dive with both water and air in the BC bladder.

Mostly though, you should just be patient and not beat yourself up over this, as the situation you were in is one of the most challenging for new divers; lots of exposure protection, which means big changes in volume over small amounts of depth change when you're close to the surface. Add in some current, a near empty tank, and it takes some skill to hold a stop at very shallow depths. You'll almost certainly develop that skill with a little more practice.

As far as the weight goes, you really should take some time at the end of a dive to experiment and see what the real minimum is to hold a stop at around 10 ft. You can do this with a buddy, just get vertical, make sure all the air is out of your BC, cross your legs, and start passing weights until you just can't help but head up. Of course, you'd want to do this after any safety stop, or maybe even just in a pool. You have to be pretty calm so you can exhale fully. I would suggest starting vertical because I think it's a bit easier to make sure everything's out of the BC and it's easier to pass some weights back and forth. Once you have what you think is the right weight, go horizontal and you'll probably find it's a little easier to keep depth.

One of the PADI courses I think is a good one, with the right instructor, of course, is the peak proficiency buoyancy. Personally I think that ought to be part of all OW courses. (or something like it)

 

[gcbryan]

You do need a weight check but it sounds to me like you might be under weighted as you suggest.

The best technique however is to make sure you are completely horizontal as you get closer to the surface so that if you do feel yourself getting light you can lower your head just a bit and kick and now you will be a few feet lower with less pressure and more time to deal with the situation.

Everyone had those problems in the shallows. I know I did and the key was just learning to anticipate when I was getting lighter when I could still do something about it. If you don't realize it until you are going up it's too late for the most part.

I would also add that when ascending you should be able to stop at any time. Once you have that kind of control this kind of thing won't happen.

Just do a weight check at the end of your next dive under calmer conditions. If you can't stay down no matter what you do you need more (a little more) weight. Otherwise it's just a technique thing and that comes with more experience.

When you are already light and you raise your body up (by going vertical) to vent that can accelerate the problem as well as any trapped air just expands even more.