Drysuit or BC for boyancy control?

[mmerriman]

There is a performance requirement in the drysuit course that requires the student to achieve neutral buoyancy using only the suit. This is completely logical seeing as how they are learning how to control the suit. That is not the same as recommending that they dive like that at all times in every circumstance.

there is no such requirement int he PADI Drysuit course.

 

[OMANDIVER]

So, I will repeat where I started with this. There are not two schools of thought. There is only the reality that no matter what you do, you will have air in your suit. If the bubble gets too big to be comfortable, which can happen with certain suits, especially as you go deeper, then you need to use the BCD. Nobody on the planet -- regardless of agency -- is going to teach you anything else, because it would be completely absurd to tell someone that they need to put all of the air in the suit even when they do not find it comfortable.

The PADI drysuit specialty book and some of the technical specialties address it along these lines although in the side-bar to this discussion a number of people have pointed out that the materials are not consistent. As I pointed out in the second post there are historical reasons that can help you understand why this recommendation existed at all, but those reasons are no longer relevant to modern divers.

The materials get updated slowly and the swarm-think on the innerwebs even more slowly. As you can see on this thread, even some IDC's are confused about what exactly needs to be taught, even though it's crystal clear once you actually start teaching people to dive dry that there is only one possible "school of thought", namely what I said above.

As for why some people prefer more squeeze, I would submit that for more or less the same reason that some people tie their shoelaces tighter than others.

R..

Just for the record, the PADI Dry Suit Diver manual 2010 has the following guideline; 'Always wear a BCD for surface flotation and buoyancy control. While underwater use your dry suit for buoyancy control. Note this community guideline does not apply to neoprene or tec diving drysuits.'

 

[mmerriman]

Page 156 in the Adventures in Diving (version 2.10), Dry Suit Diving, section "Dry Suit Buoyancy Control Underwater" is pretty clear about using the dry suit completely for buoyancy, except for emergency. I'll have to check the course manual separately.

nope. read the latest AOW info ..no such requirement - and in fact int he guide to teaching it clearly states:
7. Divers may either use their suits to control buoyancy underwater or add enough gas to the
suit to avoid suit squeeze and otherwise control buoyancy with their BCDs, depending
upon suit type, manufacturer recommendations and personal preferences.

 

[wetb4igetinthewater]

Why does the discussion have to descend into which agency says what? The question was 'why are there two schools of thought'. There clearly are two schools of thought, and what agency a or b teaches doesn't really matter.

So why do some people prefer to use the suit for squeeze only, and others prefer to use it for full buoyancy compensation?

Some of us are instructors and do not wish to violate standards. As a PADI instructor, I must teach the PADI curriculum. I then try to add optional value to give my students to further improve their diving skills.

 

[Storker]

If the bubble gets too big to be comfortable, which can happen with certain suits, especially as you go deeper [...]

I'm not with you. If I'm neutral at 3m, my suit bubble should be just the same size as if I'm neutral at 30m, no? The only exception I can think of would be if you're using a suit made from thick uncompressed neoprene, but IME those aren't particularly widespread these days.

The way I do it is to use my BCD to compensate for the weight of my gas (which slowly decreases during the dive, so I vent my BCD gradually), and add air to my suit as I descend to stay comfortably unsqueezed. My suit bubble stays the same size, and my buoyancy is virtually unchanged whether I'm at 3m or 30m.. On ascent, I vent from my suit, keeping my bubble the same size and my buoyancy pretty constant. By the end of the dive, my BCD is usually pretty empty so I have to vent a little extra from my suit to stay neutral, and surface just a little bit shrink-wrapped.

 

[wetb4igetinthewater]

nope. read the latest AOW info ..no such requirement - and in fact int he guide to teaching it clearly states:
7. Divers may either use their suits to control buoyancy underwater or add enough gas to the
suit to avoid suit squeeze and otherwise control buoyancy with their BCDs, depending
upon suit type, manufacturer recommendations and personal preferences.

Looking at my dive slates and the course material, I stand corrected! Thanks for chiming in. Boy, I made it harder for a few folks....

 

[TotDoc]

Over the course of my diving career, I did a full 180 regarding my stance on this. I started diving my drysuit purely in a recreational diving arena. It was very comfortable and easy to use just the suit for buoyancy, but I found later that it probably isn't the best way to go, and that I had likely developed some very tough to break habits by diving that way.

When I started diving doubles and sidemount, still all at recreational depths, it was still pretty easy to maintain buoyancy with just the suit, but I started noting that it was requiring quite a bit of air on every dive just to run the suit. This was on normal open water dives, where depth changes, especially need for repetitive ups and downs, were rather limited. Where this became undeniable, however, was when I used a drysuit inflation bottle with a reg setup that didn't have a dedicated inflation hose for the drysuit - I quickly found the bottle empty. As I moved into cave diving, that is where I really started noticing a difference.

Cave diving involves a lot more changes in depth that aren't exactly optional. If the cave goes up and down, so do you. I noticed that in areas 60 foot or less, when there was a swing in depth of 15 feet or more, it started getting very difficult to keep good control of my buoyancy, and I was constantly adding and dumping gas from my suit. In trying to keep my position steady in relation to the cave ceiling and floor, it became painfully apparent that I needed to work hard to stay where I wanted to be. I thought this was all just part of the process of getting used to the task loading of cave diving, though, and didn't consider that my chosen management of my drysuit was part of the difficulty.

Where I finally had my lightbulb turning on moment, though, was when I started diving a rebreather. During my initial classwork, there were a lot of dives in the 60-100 foot range, and the instructor intentionally had me changing depth -- a lot. With the rebreather on, I needed to add a TON of gas to the suit at depth, and even a little to the BC to keep things level. When I would ascend, dealing with the suit, the BC, and the rebreather loop started getting a little overwhelming -- particularly since you can't use depth of breathing to adjust your buoyancy on a rebreather. I also noticed that I continued to drain my drysuit inflation bottle every dive, as this was now a standard thing for me to use with the way I plumbed my rebreather. Around that time, my instructor told me "hey, it looks like there's a lot of gas in your suit." But...but...yeah, he was right.

From that point forward, I started adding just enough gas to keep the suit squeeze comfortable, and started adding gas to my BC to manage buoyancy changes. This made an immediate and obvious difference in regards to how easily I could manage depth changes. It also markedly changed the amount of gas I was using each dive. The suit is a LOT bigger than the BC, after all. All in all, I would be minimizing things to say it was a night and day difference how much easier and better things seemed to work using the BC for primary buoyancy control.

Where I KNEW it was better to always run the BC for buoyancy control, however, was when I did my next open circuit cave dive, and I tried the BC for control strategy. I had a significant improvement in my penetration distance before I hit 1/3rd of my tanks. I suppose this is because I was using less gas to keep my suit inflated, and even more importantly, it was easier to swim since I wasn't pushing such a large profile through the water. A suit that was not as full all the time was significantly easier to swim, and I remember noticing that it felt like I was "lighter" in the water. That led to me being actually lighter - as I was able to drop the trim weight I had been carrying on my subsequent dives, since I had less air in my suit to offset with lead. Then I started wondering why I ever did it with just the suit in the first place.

I suppose the answer to that is easy - running buoyancy with just the suit was simple and effective at recreational depths and wearing a single tank, and I never knew the shortcomings it would have later on in my diving career. In fact, I bet if I never did tech diving, I would still be using my suit only for buoyancy control, I would feel comfortable that I had it all "figured out," and I'd likely teach my students the same way. If this is the way you intend to dive, and you know that you are never going to do any tech diving, then by all means - feel free to stick with the suit only as your buoyancy control at depth. If you are just starting out with diving a drysuit and you feel like the task loading is too high, then for now, feel free to use the suit until you are getting the hang of managing an extra air space. But if you think that SOMEDAY you might want to dive in a tech config, or you are feeling very comfortable managing your drysuit, maybe it would be worth trying a little less air in the suit, and a little more air in the BC - just to see how it treats you. Who knows, you may even like it! And maybe it will be paving the way for a less painful learning curve in the future if you advance in your diving.

Even if you think that you will never do tech diving, take a lesson from me - I told myself as little as 2 years ago that I would NEVER be interested in cave diving. And now, I can't get enough. The thing I have learned time and time again with diving is that I can never say "never" in regards to where I think my diving will take me. The more I experience, and the more I learn, the more I realize that the trajectory of my diving career is always subject to change. Who knows where my diving will take me tomorrow?

 

[Diver0001]

there is no such requirement int he PADI Drysuit course.

Er... yeah, you're right. I have no idea what weird logic led me to write that. I think I was comparing it to the neutral hover in the OW course and wrote it based on how I personally do things.

In any case with so much he-said-she-said about this I actually ended up looking it up. In the instructor's manual it mentions using the suit only once that I could find. It's mentioned as a bit of a foot note about widely accepted practices, which, as previously mentioned, is out of date. It is, indeed, not a performance requirement.

There are obviously several performance requirements related to neutral buoyancy but the course does not stipulate how the student is supposed to achieve that. I guess I've gotten into the habit of doing it like this on the assumption that if they are going to learn how to control the suit that they should have to control suit. But that's just my own approach, not a standard.

R..

 

[Diver0001]

I'm not with you. If I'm neutral at 3m, my suit bubble should be just the same size as if I'm neutral at 30m, no? The only exception I can think of would be if you're using a suit made from thick uncompressed neoprene, but IME those aren't particularly widespread these days.

There are other factors that can cause a buoyancy swing but in my experience deep diving always causes it to some extent. I once had a 5mm compressed neoprene suit that quite suddenly... sort of ... collapsed I guess is the best way to describe it, if you go deep enough. It caused the suit to suddenly lose significant buoyancy.

Likewise, depending on the undergarment, you can see a buoyancy swing due to depth.

You must know this. You dive a lot in a drysuit. Haven't you noticed?

R..

 

[OMANDIVER]

Over the course of my diving career, I did a full 180 regarding my stance on this. I started diving my drysuit purely in a recreational diving arena. It was very comfortable and easy to use just the suit for buoyancy, but I found later that it probably isn't the best way to go, and that I had likely developed some very tough to break habits by diving that way.

When I started diving doubles and sidemount, still all at recreational depths, it was still pretty easy to maintain buoyancy with just the suit, but I started noting that it was requiring quite a bit of air on every dive just to run the suit. This was on normal open water dives, where depth changes, especially need for repetitive ups and downs, were rather limited. Where this became undeniable, however, was when I used a drysuit inflation bottle with a reg setup that didn't have a dedicated inflation hose for the drysuit - I quickly found the bottle empty. As I moved into cave diving, that is where I really started noticing a difference.

Cave diving involves a lot more changes in depth that aren't exactly optional. If the cave goes up and down, so do you. I noticed that in areas 60 foot or less, when there was a swing in depth of 15 feet or more, it started getting very difficult to keep good control of my buoyancy, and I was constantly adding and dumping gas from my suit. In trying to keep my position steady in relation to the cave ceiling and floor, it became painfully apparent that I needed to work hard to stay where I wanted to be. I thought this was all just part of the process of getting used to the task loading of cave diving, though, and didn't consider that my chosen management of my drysuit was part of the difficulty.

Where I finally had my lightbulb turning on moment, though, was when I started diving a rebreather. During my initial classwork, there were a lot of dives in the 60-100 foot range, and the instructor intentionally had me changing depth -- a lot. With the rebreather on, I needed to add a TON of gas to the suit at depth, and even a little to the BC to keep things level. When I would ascend, dealing with the suit, the BC, and the rebreather loop started getting a little overwhelming -- particularly since you can't use depth of breathing to adjust your buoyancy on a rebreather. I also noticed that I continued to drain my drysuit inflation bottle every dive, as this was now a standard thing for me to use with the way I plumbed my rebreather. Around that time, my instructor told me "hey, it looks like there's a lot of gas in your suit." But...but...yeah, he was right.

From that point forward, I started adding just enough gas to keep the suit squeeze comfortable, and started adding gas to my BC to manage buoyancy changes. This made an immediate and obvious difference in regards to how easily I could manage depth changes. It also markedly changed the amount of gas I was using each dive. The suit is a LOT bigger than the BC, after all. All in all, I would be minimizing things to say it was a night and day difference how much easier and better things seemed to work using the BC for primary buoyancy control.

Where I KNEW it was better to always run the BC for buoyancy control, however, was when I did my next open circuit cave dive, and I tried the BC for control strategy. I had a significant improvement in my penetration distance before I hit 1/3rd of my tanks. I suppose this is because I was using less gas to keep my suit inflated, and even more importantly, it was easier to swim since I wasn't pushing such a large profile through the water. A suit that was not as full all the time was significantly easier to swim, and I remember noticing that it felt like I was "lighter" in the water. That led to me being actually lighter - as I was able to drop the trim weight I had been carrying on my subsequent dives, since I had less air in my suit to offset with lead. Then I started wondering why I ever did it with just the suit in the first place.

I suppose the answer to that is easy - running buoyancy with just the suit was simple and effective at recreational depths and wearing a single tank, and I never knew the shortcomings it would have later on in my diving career. In fact, I bet if I never did tech diving, I would still be using my suit only for buoyancy control, I would feel comfortable that I had it all "figured out," and I'd likely teach my students the same way. If this is the way you intend to dive, and you know that you are never going to do any tech diving, then by all means - feel free to stick with the suit only as your buoyancy control at depth. If you are just starting out with diving a drysuit and you feel like the task loading is too high, then for now, feel free to use the suit until you are getting the hang of managing an extra air space. But if you think that SOMEDAY you might want to dive in a tech config, or you are feeling very comfortable managing your drysuit, maybe it would be worth trying a little less air in the suit, and a little more air in the BC - just to see how it treats you. Who knows, you may even like it! And maybe it will be paving the way for a less painful learning curve in the future if you advance in your diving.

Even if you think that you will never do tech diving, take a lesson from me - I told myself as little as 2 years ago that I would NEVER be interested in cave diving. And now, I can't get enough. The thing I have learned time and time again with diving is that I can never say "never" in regards to where I think my diving will take me. The more I experience, and the more I learn, the more I realize that the trajectory of my diving career is always subject to change. Who knows where my diving will take me tomorrow?

Amen to that. Absolutely spot on.