Ascent with little or no air in BCD??

[Mndiv]

Hey guys, I am (turned in July) 16 (got my cert when I was 15) and me and my dad went diving in Lake Ore-Be-Gone, MN. The sport is still new to us, but I can tell that I have pretty much found a love for diving thats gonna last me a lifetime!

One thing that we struggled with though as our ascent. Descent was no problem on the first dive, we went to 60 feet and swam around for a while, however as the water was quite murky we would look at our computer and notice all of a sudden that we were ascending quite fast and seemingly before we knew it, I could see the waves on the surface. We went up to fast thats for sure, and it certainly got my heart rate going but when I think about it it took us about a minute or so to the surface, (we weren't at 60 ft for very long), and thats about a foot per minute which is a descent ascent rate.

One thing to add would be that our computer (we have the same one, the Genesis Resource Pro In-Line console) has, in my opinion a bit too conservative of a ascent rate indicator, because if your below 60 ft it suggests a MAX ascent rate of 30 ft per min. at any time. If you ascent for 5 feet at a rate of 60 ft per min, you have and ascent rate 'violation' which is annoying because I never have a dive were I ascend no faster than 30 ft per min at any on point...

But heres my question: On the second dive of the day in an effort to avoid that situation again, I added 2 more pounds of weight (which ended up being to much because I was overweighted a little) and dove with little air in my BCD. When it was time to start making our way to the surface from 55 ft I let all the air out of my BCD (our instructor told us, NEVER use your BCD as an elevator, always let ALL the air out), and started kicking to the surface, which became very tiring very fast. It was sort of a anxious feeling because I would look at my depth gauge and notice that I was going up very very slowly but as soon as I stopped kicking I would slowly start descending again, so it took a lot of energy for me to make it to the surface.

Do I have to let ALL the air out of my BCD, or is it just most of it? Just some general advice to the newbies would be great!

 

[BabyDuck]

time for a good weight check. what you're describing sounds like you may be overweighted, using a decent bit of air at 60ft to be neutral, and having it expand faster than you can get rid of it on the way up. very very common.

if your weight is spot on when you do a check, to come up - take a deeper than average breath and pause. you should start slowly floating up. breathe out and dump a bit from your bc. repeat repeat repeat. firm note - i'm not talking about holding your breath for all the 60ft up! more like using the air in your lungs to begin to drift upward, then breathing out so you pause your ascent at say, 57 ft.

it's all in the practice! you'll get it!

 

[danvolker]

Hey guys, I am (turned in July) 16 (got my cert when I was 15) and me and my dad went diving in Lake Ore-Be-Gone, MN. The sport is still new to us, but I can tell that I have pretty much found a love for diving thats gonna last me a lifetime!

One thing that we struggled with though as our ascent. Descent was no problem on the first dive, we went to 60 feet and swam around for a while, however as the water was quite murky we would look at our computer and notice all of a sudden that we were ascending quite fast and seemingly before we knew it, I could see the waves on the surface. We went up to fast thats for sure, and it certainly got my heart rate going but when I think about it it took us about a minute or so to the surface, (we weren't at 60 ft for very long), and thats about a foot per minute which is a descent ascent rate.

One thing to add would be that our computer (we have the same one, the Genesis Resource Pro In-Line console) has, in my opinion a bit too conservative of a ascent rate indicator, because if your below 60 ft it suggests a MAX ascent rate of 30 ft per min. at any time. If you ascent for 5 feet at a rate of 60 ft per min, you have and ascent rate 'violation' which is annoying because I never have a dive were I ascend no faster than 30 ft per min at any on point...

But heres my question: On the second dive of the day in an effort to avoid that situation again, I added 2 more pounds of weight (which ended up being to much because I was overweighted a little) and dove with little air in my BCD. When it was time to start making our way to the surface from 55 ft I let all the air out of my BCD (our instructor told us, NEVER use your BCD as an elevator, always let ALL the air out), and started kicking to the surface, which became very tiring very fast. It was sort of a anxious feeling because I would look at my depth gauge and notice that I was going up very very slowly but as soon as I stopped kicking I would slowly start descending again, so it took a lot of energy for me to make it to the surface.

Do I have to let ALL the air out of my BCD, or is it just most of it? Just some general advice to the newbies would be great!

I like that your instructor taught you not to use your BC as an elevator, and that you are always "swimming your way up"....but I would suggest allowing enough air to remain in the BC so that you are neutral or just a tiny bit negative...there is no reason to work your butt off on the ascent....the complication is that you now have one more task to stay on top of....to regulate the dumping of air from the BC all the way to the surface..this is something most divers do, so it should become easy for you..but you do need to stay on top of it all the way up.

 

[TSandM]

There are two schools of thought on ascents. One, the one your instructor taught you, is to do your ascent negative, and provide the upward movement with your fins. There are two issues with that that you have already discovered. One is that it's work, and the other is that, if for any reason you stop kicking, you immediately sink.

The other school is that ascents (like most descents) should be carried out with the smallest deviations from neutral that are necessary to ascend. If you are neutral, just filling your lungs and breathing at the "top" of them for a few seconds should start you upward, and expansion of gas in the BC will continue the process until you vent some air. This technique may take a bit more practice, and of course, you do have the risk that you may not vent in time and end up ascending too fast, which is why practice with this is best done on fairly shallow dives, until you have the idea down fairly solid.

If you are diving in very low viz, where you have few visual references, it can be quite difficult to notice excursions in depth. Going down, your ears will eventually let you know, but if you are distracted, you may not notice ear pressure until you have moved quite a ways in the water column. Going up, some people get information from their ears (squeaks or pops) but some of us get none. You have to notice you are rising by feeling the expansion of your BC or watching the small particles in the water (if they're going down, you're going UP) or just by watching your depth gauge. Managing yourself in green water can be challenging, even to divers with much more experience than you have.

I concur with the idea of doing a good, formal weight check, rather than just randomly adjusting weight. More buoyancy errors in new divers are due to overweighting than to underweighting, but both make a well-executed dive difficult.

 

[w ripley]

I don't dive with anyone who lets all of their air out of their BC/wings before going up. Understand Boyle's law, and agree that you don't add air to go up, but you want to stay neutral during your entire dive. Making yourself heavy, by removing the lift from your BC, may be safe for starting out (and only if you aren't burdened down with deco bottles, etc.) but puts an extra amount of work on you at depth. Actually, I think your instructor is taking the easy way out by not teaching you proper buoyancy from the gitgo. We've got too many of those instructors, unfortunately, IMO. Adding extra weight - not to make yourself neutral in the water column - is going to compound the issues.

I need the lift to stay neutral, and will start venting as I go up. I always go up with my body horizontal, and not vertical, as being vertical helps me to stay in control.

The trick in diving is to always go slowly, no matter what you are doing, and always be in control of yourself where ever you are in the water. On a drift assent, for example, when you may not have any visual references to judge if you are going up or down, it's your depth gauge that you will depend on, so you really have to take everything slowly as those things take a second (or two) to register your change in depth. If you shoot a bag, then you have a vertical line to help judge your position in the water column.

As said in the last post, it just takes practice. I've been doing this for a long time and know how quickly things can get away from you, especially in out-of-control assents. BTW, you should also practice for out-of-control assents, so you will know what to do when they happen, and they will. If you don't get it down when you're at 60 feet, what on earth are you going to do when you are at 100, 200, 300, etc. feet.

You're on the right track by asking and I'm sure you're going to get a lot of good advice on this thread. Good luck.

 

[g1138]

In short terms:

- Ascent Rate has been changed to recommend 30ft per min. Most if not all agencies recommend this ascent rate now
- When you ascend use your BC to stay neutral, but not positive.
-----> this means do NOT dump all the air out of your BC but keep enough so that if you stop kicking you won't start sinking at an alarming rate

This takes practice and proper weighting.


Long answer:
You instructor was watching out for you by telling you to let all the air out of your BC. It's a train of thought that's not followed by all instructors. (It is not the right or wrong train of thought either)
At the newbie stage that you're at, it's common to have a runaway ascent, since you have yet to have enough experience to gauge when you're ascending outside of your own power and when to vent at the right time.
However this train of thought does not work for deep dives where you lose a lot of buoyancy in your wetsuit. You're actually more negatively buoyant at 60ft than at 30ft, so much so that you could ditch a few pounds and still stay down at 60ft. Divers don't do this however because they weight themselves to be neutral at 20-15ft with a low tank. It's so they can be neutral at their safety stop.
This is the reason why you had trouble ascending during this dive but probably not during your checkout dives.

Weight yourself so you can conduct a safety stop with little air in your BC at the end of your dive. When you ascend, dump enough air to keep you neutral. You can get a little negative, but with experience you can use your lungs as your fins and ascend without kicking.
(see example video)

[video=youtube;OXwQTU1z1t0]http://www.youtube.com/watch?v=OXwQTU1z1t0&feature=related[/video]

 

[TMHeimer]

As I am quite often right on the bottom (not flopping around harming anything) looking for shells in the sand, when I begin my ascent I do put a little air in the BC, so I'm starting off neutral or close to it. Otherwise, as you say, it can be a lot of work kicking up with a near empty BC, especially when just starting up, as the differences in pressure at depth are less than closer to the surface. Then, as pointed out, you must monitor your ascent rate closely and vent accordingly. Once in a blue moon I still vent a little too much on the way up and the ascent stops, meaning more fin work. It's not an absolute exact science (well, is it physics-wise), but it's more of an Art.

 

[DevonDiver]

...in my opinion a bit too conservative of a ascent rate indicator, because if your below 60 ft it suggests a MAX ascent rate of 30 ft per min. at any time. If you ascent for 5 feet at a rate of 60 ft per min, you have and ascent rate 'violation' which is annoying because I never have a dive were I ascend no faster than 30 ft per min at any on point...

I'm not sure what your opinion has to do with it. The ascent rate is applicable to the algorithm used by the computer - therefore, it is as valid as any other information the unit may produce. If that algorithm demands you ascend at 30ftpm, then you need to ascend at 30ftpm. A faster ascent takes you beyond the safe parameters that the computer uses to calculate your offgassing.

I'd suggest reading Mark Powell's 'Deco for Divers'.

It's also worth noting that 60ftpm is a maximum ascent rate. Like a speed limit. There's no obligation (and little safety margin) in aiming to ascend right upon that maximum rate. As others have mentioned, most agencies use a much slower rate.... PADI have used the 60ftpm rate since they released the RDP (7 years before you were even born)...and there are legal reasons why they are reluctant to alter that recommended ascent rate now to bring it in line with other agencies at a slower speed.

On the second dive of the day in an effort to avoid that situation again, I added 2 more pounds of weight (which ended up being to much because I was overweighted a little) and dove with little air in my BCD.

Overweighting makes ascents harder, not easier. You need more air in your BCD to compensate for the unnecessary weight. More air = more expansion, especially in the shallows.

Have a look at the article series: Scuba Buoyancy Masterclass 1of9 - Buoyancy Control for Scuba Divers -Scuba Tech Philippines

When it was time to start making our way to the surface from 55 ft I let all the air out of my BCD (our instructor told us, NEVER use your BCD as an elevator, always let ALL the air out), and started kicking to the surface, which became very tiring very fast.

That's a great way to ignite a scuba accident. It won't take much task loading, cramp, immobilisation, or any other type of distracting incident, to see you descending again. If you get distracted, then your finning may also result in an uncontrolled ascent.

Ascend neutrally, or slightly negatively, buoyant - you should be able to initiate your ascent with a slightly deeper inhalation and arrest your ascent (and hover) by breathing shallower...dumping tiny amounts of air from your BCD as you ascend to compensate for the small amount of air expansion in your BCD and exposure suit.

Proper weighting is the foundation of this... plus the cultivation of instinctive and constant neutral buoyancy throughout the dive.

Do I have to let ALL the air out of my BCD, or is it just most of it? Just some general advice to the newbies would be great!

If your weighting is correct, then you shouldn't require much air in your BCD to start with. The only air you put in your BCD should be to compensate for exposure suit buoyancy loss due to compression. As the dive progresses, your tanks may become more buoyant - so you'll start dumping small quantities of air during the dive (at a given level). On ascent, your exposure suit will expand back towards its normal thickness (and buoyancy characteristics)...and you'll dump air as a reaction to that. By the time you reach your safety stop, with most of the gas in your cylinder consumed and your exposure suit at full buoyancy, you shouldn't require any air in your BCD.

The proper fine-tuned weight check reflects this state. Hover at 5m with your cylinder at reserve level (500psi), empty your BCD and start removing weights until you can only just maintain a hover (positive buoyancy). This will dictate your actual maximum weight requirement (for more details, see the article series above).

 

[boulderjohn]

First of all, let's be sure you understand what happened the first time. I assume that diving in Minnesota, you had a thick we suit on, and that is important, as you will see. As you descend the wet suit compresses because of pressure, as does the air in your BCD. You can add air to the BCD, but you can't add air to the wet suit. So when you are at the deepest part of your dive, you have added a lot of air to your BCD, but your wet suit is still very much compressed. If you have a thick wet suit, you had to have a lot more weight near the surface to sink than you need at the bottom while you are diving. Anyone who dives with a thick wet suit is overweighted during the dive--you have no choice.

So you begin your ascent. The air in our BCD starts to expand, and so does the gas in your wet suit. At first the expansion is not that much, but the closer you get to the surface, the faster they expand. In the last 15-20 feet, if you don't take care of things, you will be shooting up like the submarine in Hunt for Red October. What you have to do to take care of it s anticipate that change and let out puffs of air as you ascend so that you don't go out of control.

As Devon said, adding more weight makes the situation worse. You are even more overweighted at the bottom, so you need to add more air to bet neutral. That air will expand even more when you ascend, and once again you are on a rocket ride to the surface.

Taking all the air out before ascent only works in warm water, with thin wet suits, and then only if you are properly weighted. In that case, you will be strong enough to make it to the surface easily just by kicking. With a thick wet suit and the consequential overweighting at depth, you will be fighting to get to the surface. As others have said, the proper way is to ascend is to start neutral. As you ascend, pay attention to what is making you ascend. It should be your gentle kicking that is doing it. You should have a hand on one of the air dumps at all times, so that if you feel your BCD pulling you up instead, you can dump enough air so that you are back in control.

Finally, when the PADI dive tables were created, 60 FPM was the accepted ascent rate, so all the experimentation that went into those tables was based on that ascent rate. All the table figures are safe at that ascent rate, but the ascent rate is figured into those figures. More recent research has found that 30 FPM is better, but PADI can't change to that because it would make the figures on the dive table wrong. The difference is subtle, but they cannot make the change officially without redoing all that expensive research. Technically, if you do 30 FPM (and you should), you should leave the bottom a tad earlier than the official figures, but it is not something I would worry about.

 

[DevonDiver]

You instructor was watching out for you by telling you to let all the air out of your BC. It's a train of thought that's not followed by all instructors. (It is not the right or wrong train of thought either)

Really? I think it is quite categorically wrong.

Dumping all the air from your BCD, then attempting to ascend totally negative is a recipe for an accident.

In the long term, it will really stifle the development of a divers' instinctive buoyancy control.

In the short term... it makes the instructors' job so much easier.... so what the heck? Over-weight 'em and tell them to ascend negative...

Over-weighted, negatively buoyant, knee-dwelling students.... flying the flag for lazy instructors around the globe! :depressed: