Scuba 101 – Controlled ascents
One of the most important skills for new scuba diver to master is a controlled ascent. It is not uncommon for newer divers to feel okay at depth (>30′) but then feel unstable on ascents and in shallow waters – “I can hold my 20′ safety stop, but when I move shallower, I quickly find myself on the surface.” This is especially true for new cold water divers and new drysuit divers.
Fortunately, controlled ascents can be learned.
Picture by Toine Peeters
Proper Weighting
Carrying the appropriate amount of weight makes diving easier. Carrying too much weight adds instability into the scuba system, as more air is needed to compensate for the additional weight.
Obviously, it’s possible to manage the extra weight. But why do so when it’s unnecessary and makes diving more difficult?
Proper weighting is achieved when a diver can hold a 10′ stop without any air in the BC and with 500psi remaining in the tank. This insures that the diver can hold his last stop at the end of a dive.
Be a Proactive Diver
The most common statement I make while teaching a basic scuba course is “be a proactive diver. And not a reactive diver.”
Instead of waiting to react to buoyancy changes, it’s better to anticipate and proactively manage. On descents, this means adding air as one descends and thus stopping a few feet from the ocean bottom. An example of being reactive on descents is the diver that touches down on the ocean bottom and then adds air to lift him off the bottom and into a neutral state.
On ascents, being proactive means dumping gas from the BC when the diver ascends, before feeling a positive buoyancy effect. On an ascent from depths greater than 30′, this generally means dumping gas every 5′-10′ as appropriate. For ascents from 30′, this may mean dumping gas every 2′ or less, depending how you are managing your ascent rate and ascent strategy.
Getting in Front of the Buoyancy Curve
To be proactive on ascents, this means that the diver must get in front of the buoyancy curve.
Instead of adjusting once you get to the desired depth, adjust en route.
For the ascent, this means adjusting during the ascent, before you feel the buoyancy lifting you up. To do this, the diver uses the combination of lung and BC to manage the ascent.
Simplified, the steps would be as follows:
- Start neutral in the water column
- Inhale to start the ascent
- Dump gas
- Exhale back to normal lung volume
- You should now be neutral in the water column
- Repeat 1-5
Remember that the recommended ascent rate is 30′ per minute. That means from a typical safety stop of 20′, it should take the diver 40 seconds to reach the surface.
A proper ascent and bubble management would look something like below. The bubble is appropriately sized for the ascent, and not pulling the diver up and out of control.
If the diver waits too long to manage his buoyancy, and gets behind the bubble curve, then the extra air in the BC will cause a rapid and potentially uncontrolled ascent.
The excess bubble (buoyancy) causes the diver to rise. This expands the bubble more and in turn causes the diver to rise faster and expand the bubble even more. I think that all of us in our diving career has felt the sensation of being carried away to the surface.
Body Position
While I discuss body position in the scuba ascents and descent article, its worthwhile to revisit again. The horizontal trim position offers the diver stability while moving up and down the water column. This is because the horizontal trim position provides the largest vertical drag possible.
Please refer to the linked article above for a more detailed discussion of body position.
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Don, all of it makes sense, with the exception of the ascent, how do you ontinue to vent your BCD while in a horizontal position? Is it better to use the back dump in this case?
Kristina,
Thank you for reading the article.
Regarding venting of a BC, it is ideal to use the back dump. The best way to find the butt dump is to grab the dump, and then feel towards the center to get the string.
However, using the inflator hose is possible as well. Just insure that you are extending the hose up fully and do a slight roll to bring the left shoulder up. The most common issue is that the hose is not fully extended, and it’s not the highest point on the body.
Don,
Thanks for posting! Your article on controled ascents is helpful!
Don
I like your sequence on ascent.
Do you consider thirty ft per minute ideal or a maximum? I try to go much slower the last 20 ft or so.
@Kathy: Thanks for reading!
@Brian: 30′ per minute ascent rate is the DAN recommended ascent rate. Like you, I’m much slower the last 20′. Using MDL Ascent profiles, I’m 1 minute at 30′, 1 minute at 20′, and 1 minute at 10′. As the result, my shallows are slower too.
Btw, we’re overdue for a dive together!
I’m fairly new (17 dives) and I have a problem with uncontroled ascent once I reach 25-30′. I ascend in the vertical, venting (SS1) in the near vertical (there is a bend in the hose due to velcro keeper). Everything is fine until I get to 25-30 feet and here I go. I have tried increasing weight (no good) tried getting advice…..one guy said your SS1 is trapping air, that’s why I said ‘near vertical, bend in hose’.
Could my BC be trapping air. It’s a back inflate Aeris Reef Rider. Can you help?
thanks, Joe
Joe,
Hi. A few questions for you:
(1) When you vent from the inflator hose (SS1), do you see bubbles venting?
(2) How often are you venting when from 30′ to the surface?
(3) Are you ascending by kicking up?
Regarding bend in the hose, a bend is okay as long as the bend is L shaped and not U shaped. For newer divers, it’s not uncommon to not expend their arms fully, thereby not creating a straight enough path for air to escape.
It could be possible that the BC is trapping air, though the Aeris Reef Rider’s BC looks pretty compact. If you’re ascending in the vertical position, it’s very unlikely that trapped air is occurring though. In the vertical position, the inflator hose should be at the highest point. You can check that in the BC.
Thanks.
-Don