I f*** up and I am ashamed

[Dody]

I am having trouble understanding this. Perhaps we are not all using the same definitions for key words.

There are three possible conditions:

1. underweighted
2. perfectly weighted for neutral buoyancy
3. overweighted

As I define "underweighted," you cannot dive underweighted because you either cannot get below the surface to begin with or you will ascend out of control later in the dive when you have lost some weight through air usage. No one can possibly suggest that it is good to dive underweighted.

I suspect that what you mean by "underweighted" is as close to perfectly weighted as possible, thus avoiding being overweighted. In that case, I can see that you might believe that. Many people do believe that, including many people who are quick to respond to questions like this on ScubaBoard.

Personally, I like being a few pounds--maybe 2 kilos-- overweighted (more than the amount needed for perfect neutral buoyancy). It allows me to descend faster than when perfectly weighted, and if I need to dump some air, it makes it every so much easier, because I can get the bubble of air to an exit point more easily. If you only have a tiny amount of air in your BCD, you may have to do some sort of gymnastics maneuver to get that tiny bubble to a dump area.

That is what I assume happened to you on the ceiling of that overhead. You still had a little bit of air in the BCD, but it was not at a dump valve, and you were unable to get it to a dump valve. I will expand on this in my next post.

Ok. I believed that I was perfectly weighted for neutral buoyancy during the dive. I could hold my safety stop with 4 Kg so I thought 4 was fine. I very rarely use my BCD during a dive. Playing with my lungs is enough. Of course, I have to struggle to go down at the beginning of the dive and be very careful at the end not to go to a runaway ascend in the last 3 meters. I figured that I would not risk an emboly and that I could always go back down. Well, I could not go back down. I was too tired. I underestimated the risk of being underweighted. Now, I would rather dive with 6 or 8 kg rather than 4. From 40 m, I ascend without inflating my BCD. I might need to inflate a bit. I hate not being in control.

 

[boulderjohn]

Let's look at your initial description of the event.

At the end of the dive, we went into a big cave with no visibility. The briefing did not mention this cave. The DM entered, my wife entered. I was at the back and I followed even though I would not have if my wife was not in front of me. I could not see anything, could not see my DC because of the poor vis and did not see my wife. Then, I realized that I was moving up. Purging air did not do anything and I ended up stuck at the cave ceiling at 2m (I checked my DC later) with my head knocking on rocks.

In that description, you said that early in the dive, while you still had plenty of air, you realized you were moving up, and you eventually reached the overhead at only 2 m of depth, which is very shallow. What would cause you to move up? You were becoming more buoyant, which happens due to expansion of gas at lesser ambient pressure (Boyle's Law). The closer you are to the surface, the more this happens. So what was expanding? It could be a wetsuit, but more likely it was the air in your BCD. This is extremely common with newer divers. The air in your BCD expands rapidly when you get near the surface, bringing you suddenly upward.

This does not suggest that you were underweighted. If you have enough air in the BCD for that to happen, you had more than enough weight, at least for that point in the dive (before air weight loss). Further, your struggles to get down strongly suggest the presence of expanded air trying to get you to the surface and being stopped from doing that by the overhead. When that happens, it can indeed be very difficult to descend, because you cannot easily get that bubble of air to the exit point. You can pull on dump valves all you want, but if that air is at a point higher than the dump valve, it isn't going anywhere.

So my diagnosis of the situation is that you had enough weight for the dive (at least at that point), and when you entered the overhead, you ascended somewhat. As you did, the air in the BCD expanded due to Boyle's Law and took you to the ceiling. Once there, you were unable to release air due to the fact that you were pinned to the ceiling and could not get the BCD air to an exit point.

 

[Dody]

I strongly suspect that you still had air in your BCD.

This is a very common problem, that I've experienced myself, where I've pulled all dump valves, rotated, etc and thought there's no way there's any more air. The way I discovered I was wrong, was I removed "all air" then removed my BCD underwater, rotated my BCD around, and noticed there were still trapped air-pockets. I started carrying just a little more weight after that, which helped significantly, because sometimes getting that last **** air pocket out is impossible.

I understand exactly why you think "I can't possibly have more air in my BCD" when you do. It's just the nature of BCDs & especially back-mount, that you should just assume there's air-trapping going on. You aren't necessarily even doing anything "wrong" if you're experiencing the problem of air-trapping. Be open-minded to the idea that this is possible, and you may very well discover it is happening.

Less commonly, you can also experience air-trapping in other areas like pouches/pockets and wetsuits.



I love the "rule of fun" and follow something very similar.

• During a "fun dive", I'll practice no more than 1-2 "new" skills. I'll also abandon that practicing if it gets in the way.
• I do periodic "practice dives," which are low-stress, minimal-depth dives for practicing skills. I'm not in a rush, air-consumption is not an issue, the surface is maybe 20ft away, and nobody is waiting for me. I still try to remain within the realm of fun, there's nobody to impress, and if something is just not working, I'll work on another skill instead.
• I also recently bought an inexpensive underwater action-camera, so I could record myself. That way if I'm just failing at a skill, I can just get a recording, move on to something else, and then review the footage later.

20 ft away? Diving to 30 meters is a routine for my wife and I. We practise OOA exercises (giving octo) from that depth.

 

[Dody]

Let's look at your initial description of the event.


In that description, you said that early in the dive, while you still had plenty of air, you realized you were moving up, and you eventually reached the overhead at only 2 m of depth, which is very shallow. What would cause you to move up? You were becoming more buoyant, which happens due to expansion of gas at lesser ambient pressure (Boyle's Law). The closer you are to the surface, the more this happens. So what was expanding? It could be a wetsuit, but more likely it was the air in your BCD. This is extremely common with newer divers. The air in your BCD expands rapidly when you get near the surface, bringing you suddenly upward.

This does not suggest that you were underweighted. If you have enough air in the BCD for that to happen, you had more than enough weight, at least for that point in the dive (before air weight loss). Further, your struggles to get down strongly suggest the presence of expanded air trying to get you to the surface and being stopped from doing that by the overhead. When that happens, it can indeed be very difficult to descend, because you cannot easily get that bubble of air to the exit point. You can pull on dump valves all you want, but if that air is at a point higher than the dump valve, it isn't going anywhere.

So my diagnosis of the situation is that you had enough weight for the dive (at least at that point), and when you entered the overhead, you ascended somewhat. As you did, the air in the BCD expanded due to Boyle's Law and too you to the ceiling. Once there, you were unable to release air due to the fact that you were pinned to the ceiling and could not get the BCD air to an exit point.

One thing is for sure. Next time I am stuck on a ceiling, if it happens, I will be remain cool as a breeze. I am the one telling all my diving friends that as long as you have air to breath, you are ok. I might have overreacted in this case.

 

[boulderjohn]

Weighting is a funny thing. It should be a simple matter of math and physics, but....

About 20 years ago, well before I had all that much experience or professional qualifications, I was diving with a friend in the ocean off Florida in the USA. He had less experience than I did. I was using my Zeagle Ranger BCD, a model which then had two waist pockets only. I had 4 pounds in each pocket--a bit less than you are using now. I had decided that 8 pounds was about right for me; I still needed a little air in the BCD, and I was very comfortable with it. If you looked at me and my friend side by side, you would assume he would be using much less weight than I, but he put a lot more weight on his weight belt than I used.

As we dived, he started struggling with buoyancy, fighting to keep from going to the surface. Later on the boat he saw that he had miscounted his weights and was diving with less than he intended. He had intended to be diving with twice as much as I was using, but he only had 12 pounds. I checked his BCD, and there was very little air in it. Not wanting to end the dive, I handed him one of my weight pockets. Carrying that with him as he dived gave him 16 pounds--twice my normal weighting, and he was able to dive comfortably again. Of course, that left me with only 4 pounds, but I was able to do the entire dive that way by taking in only the barest minimum of breath and by squeezing my torso (stomach, etc.) as much as possible.

It made no sense to me. Why on Earth did he need that much weight? And it certainly did seem like he needed it.

So I have stopped trying to figure all that out. You need what you need, and what you need will likely change over the years.

 

[SlugLife]

20 ft away? Diving to 30 meters is a routine for my wife and I. We practise OOA exercises (giving octo) from that depth.

I understand you're being bombarded by comments, but I was hoping you'd take more interest in the air-trapping comments.

Regardless, to answer your question, yes, when the dive is mostly for the purpose of practice, I usually practice skills at 15ft to 30ft. It has a LOT of benefits:

• Practicing skills shallow is more efficient, due to reduced air-consumption & ability to surface frequently without a safety stop. For example, I can easily knock out 30+ DSMB deployments on half a tank, whereas you might practice DSMB deployment once on a single tank on a normal dive. Being able to practice several hours, or get multiple dives off a single tank is awesome.
• Reduced nitrogen narcosis can also aid with ability to focus, when practicing brand new skills.
  
• Practicing skills shallow is reduced risk if something goes wrong, since you can always surface quickly. I do a lot of practice stuff solo (which is another topic), so I take extra precautions and ensure I have multiple bailout plans.
  • Even "safe" skills may occasionally carry unexpected risk, such as a DSMB dragging you to the surface, accidentally dropping your mask, or inhaling a little bit of water. Many "skills" one might practice, are scenarios where something goes wrong, and therefore in practice you often introduce a simulated problem. Most dive-accidents are the result of multiple problems at the same time; meaning a simulated problem that happens at the same time as a real problem, can lead to an accident. Your story is an example, where a two things went wrong at once, but thankfully didn't quite reach accident-level.

However, assuming you're practicing a skill, where "failing" the skill would carry no risk, sure, there's nothing "incorrect" with practicing at depth. The main downside is you're FAR less efficient due to air-consumption at depth. A single OOA exercise at depth, where you're both used to the drill isn't a big deal, and unexpected practice is often a good thing.

Perhaps the last important thing to mention is to not overdo practice on a fun-dive, as it can be very disruptive and annoying. I don't buddy-dive much, but I'd probably thumb a dive if a buddy did more than one OOA drill, unless it was discussed before the dive.

 

[Kimela]

But diving underweighted is a big mistake that I was never warned of.

I think we divers can be a proud group. We pick up the idea that there is a direct link between diving proficiency and how little weight we carry. The less weight we carry, the better diver we are thought to be. I know I'm guilty.

While it's absolutely true that as your buoyancy improves you will need less weight, it is also true that we each have different body composition, requiring more or less weight. SOMEtimes that might be explained away by percent of body fat, but not always. My husband is naturally negatively buoyant - more than the normal person - and he sinks in salt water even at his highest percent body fat. He dives with 4 pounds of weight in rash guards in Cozumel (no heavy back plate and no steel tanks).

Also, it takes time (diving) to get to the point when you know you can drop some lead. When you get to that point it will be time to do a serious and intentional weight check at the surface with a near-empty tank. Everyone says "do a weight check" like it's the easiest thing in the world to do, but it really isn't. You need to coordinate it with your buddy and maybe a guide, so they'll know why you're not just coming up the ladder at the end of the dive. It takes a few minutes. Nobody will begrudge you taking the time to do it if they know what's going on.

Use the weight you need (I'm saying this to me as much as to you) and don't give into the pressure to use less to look like a more skilled diver.

 

[BoltSnap]

Of course, I have to struggle to go down at the beginning of the dive and be very careful at the end not to go to a runaway ascend in the last 3 meters.

This means that you aren't "perfectly weighted for neutral buoyancy during the dive" at all. You were underweighted which is dangerous in itself especially at the end of the dive when you tank is more buoyant.

 

[Blackcrusader]

But diving underweighted is a big mistake that I was never warned of.

How can that be? It would be covered in your OW course so you avoid an uncontrolled ascent.

 

[drrich2]

I don't recall whether this got mentioned earlier in the thread, so if a repeat, apologies. IIRC, I've read elsewhere that over the course of a typical dive using a standard AL 80 tank, one may lose about 4-lbs. in weight due to compressed air usage. Others here may be able to give a more precise account. Bottom line - trouble getting down to start can mean more trouble later.

On the other hand...I've had some trouble getting down before, likely due to some anxiety when I've not dove for awhile - I'm concerned about how the dive will go, will my ears clear okay, will I run low on air and cut others' dive short, etc... So I may be holding more air in my lungs unconsciously.

My personal rule of thumb, and this is just me, is after doing a few dives where I've had no trouble being underweighted, and my tank is down around 500 PSI and I've finished a 15-minute safety stop, at what's likely to be my lightest point in the dive, lift my inflator up and hit the button to release air from my BCD (BP/W wing now). If a small amount escapes, okay. If a substantial amount of gas escapes, and I sink quickly...I may be overweighted.

Other divers may have better 'tricks' for determining their weighting, and I make no claims to be good at it. I like to think mine is logical and conceptually simple (i.e.: easy enough for me to do).