Buoyancy Control

[Steve Pearson]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

[tristan green]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

I think it's been said very well on another board where this same question was posted:

"Drysuit to keep you dry - BCD for bouyancy."

Currently I dive in a wetsuit - so my answer would be obvious. But when diving a drysuit I stick just enough air in to ease the squeeze and sort my bouyancy out with my BCD.

Which do you use?

Cheers,
Tristan

[Nigel Hewitt]

Some people use drysuits for buoyancy control, others use their wing or BCD.

The dry suit keeps me dry and I leave the autodump wide open so it really is auto. The Wing controls buoyancy as it is a BCD (Buoyancy Control Device). You can fudge it with the drysuit alone but only if your are diving a single and a bit under weighted. I really don't have that option with the RB as I can't fudge out the errors by how much breath I hold as it doesn't make any difference so I have to do it properly.

That said you need to learn to fly on the suit for the day something breaks and you need to get home on what you have but that doesn't mean I have to do it every time. I paid good money for that wing...

[benpanter]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

I tend to use the drysuit only for warmth... I dive a 12x2 twinset, and over the course of a dive the buoyancy changes sufficently that I need a fair bit of air in whichever device at the beginning of the dive to remain neutral by the end. I don't like the "Mr. Blobby" results of diving a suit with lots of spare air in it, so use the wing instead.

I usually tell people during the buddy check, just as a reminder on the off chance they have to lift me. I've dived with clubs whose dogma is to only use the bcd on the surface... I've never really understood the logic to be honest.

HTH,

Ben

[Andy Wade]

:=Some people use drysuits for buoyancy control, others us their wing or BCD.
:=
:=Which method do you use and why?

I tend to use the drysuit only for warmth... I dive a 12x2 twinset, and over the course of a dive the buoyancy changes sufficently that I need a fair bit of air in whichever device at the beginning of the dive to remain neutral by the end. I don't like the "Mr. Blobby" results of diving a suit with lots of spare air in it, so use the wing instead.

I usually tell people during the buddy check, just as a reminder on the off chance they have to lift me. I've dived with clubs whose dogma is to only use the bcd on the surface... I've never really understood the logic to be honest.


Well I can explain the dogma, but not the logic.
Historically the dogma comes from a time when all we had was ABLJ's with no direct feed, and a small emergency cylinder. It gave you support at the surface, and never got used for anything else. Buoyancy control was acheived with precise weighting and within the limits of your lung capacity. If you got it slightly wrong then you really would have had to inflate the jacket with your mouth, later on direct feeds came in and things got a lot easier for buoyancy control, later still everyone had drysuits and some found it easier to use their drysuit without any lifejacket at all, so all they had was their suit. Precise weighting meant all you had to do was put enough in the suit for comfort and you could dive within the limits of your lung capacity for buoyancy control. 'Michelin Man' at the surface was good for a laugh unless you overdid it and couldn't bend your arm to dump from the cuff. No cuff dumps then. Or Auto dumps either. If you were face down.... Sheesh! Only seen that once. Yes he did have his cylinder on. Twit. He won the 'Golden anchor award' for that I think. Chortle chortle ;-)
Moving on....
Stab jackets are a bit of a half way house which put buoyancy at the back of the diver (sometimes putting them face down at the surface). They are less cluttered at the front, no big bubble of air in your face. Nice pockets. The Wing also puts you in the optimum prone diving position. (pockets now on the suit thighs) There are still people who think Stabs/Wings are unsafe because they don't stick you seriously 'face up' at the surface in an emergency. 'Heads up' but not 'face up' - not enough for some people.
I hope this explains the dogma, people get stuck in their ways because of influences from others who have had some or all of this kind of experience. They get a way to dive which works for them, and stick rigidly to it no matter what kit they have recently bought. If you've been through all that without keeping an open mind about new kit and techniques, it's easy to get stuck in your ways. Hence the dogma.

Back to the original question - I agree, ideally you would have enough in your suit for comfort with correct weighting on the belt, and use the BC/Wing for buoyancy control and an easily controlled emergency source of lift.



.

[Tony Dwyer]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

I have my weight set up with my regular rigs so that I am neutral at the end of a dive at the surface. Since I use neoprene suit, it loses bouyancy at depth. I put a little air in to remain neutral. If I'm carrying additional gear, I use my wing to manage bouyancy at depth.

The BSAC Dry Suit Training - Instructor Notes say:

DRYSUIT DIVING IN SAFETY
? Keep the suit zipped up whenever in a boat
? Make sure controls are not obstructed by other kit.
? Do not dive with excess weights on the weight belt.
? Use BC for surface inflation and emergency buoyancy
? Ensure a thorough buddy check for ALL equipment.
? Avoid overheating if zipped into a drysuit
? Use the drysuit for routine buoyancy.
? Descend feet first and add air regularly to maintain buoyancy
? Ascend under control make sure vent air from arms
? If ascent accelerates and vent valve can not cope, pull open neck seal or wrist seal.


So when teaching, I pass on the above, BUT I also say that it's OK to just take off the squeeze and use the BC. However, for newbies it does give them two volumes of expanding gas to manage.

[John Cale]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

I use both methods depending on what I'm doing. Up to 2x12 + ali 7 I use my suit. Over that I use the wing to take the bulk of the weight then trim out on the suit during the dive. On ascent forget about the suit (ah the wonders of an autodump) and use the wing coz it has most influence on my buoyancy. I tried using only the wing and just getting comfortable in the suit but I've been diving since the days of ABLJs with no direct feed (see Andy Wades post) and found myself instinctively using the suit at depth. It worked for me so I stuck with it.

I think, though, that regardless of which method you adopt you should practice the other and be competent at it so that when your chosen method goes nipples north it's nothing more than an inconvenience. It worries me when I read of people racking up a mandatory decompression obligation in one post then saying in another that the only way to control buoyancy is X way. If you won't at least practice the other way(s), where's your back up?


John

[Finless]

Suit only for me.

1. I like a bit of air in the suit - I stay warmer.
2. I get into inverted positions when diving and out again with no problem.
3. Diving just a twinset + occasionally a 3 ltr means easing the squeeze isn't far short of neutral buoyancy for me.
4. Most important (for me) is only controlling one major buoyancy source on ascent. These people that dump all the air out of their dry suit on ascent, well ...... it's bloody cold in winter. I only do a max of 30 mins deco and am suffering after 5 mins.
5. It works for me and has ever since I started diving so, if it isn't broke ..........

[Gordon Archer]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

I have dived a drysuit for some time and have tried both systems. I now use my suit alone below water dumping my BC on the surface and reinflating upon returning to the surface.
I am warm perfectly balanced, set up to be neutral at he end of the dive with the required 50bar reserve.
The control of the single source in the suit make it simpe and effective. I dive a single 12L setup with Buddy profile BC.
Teaching drysuit use this system works the trainee's seem to take to it easily, just a single in & out like a BC just in different place.
I find it easy to switch from one system to the other if required>
Once you have really learnt bouyancy control it feels the same whatever system you use.

[TerryH]

BC. However, for newbies it does give them two volumes of expanding gas to manage.:=

Important point that.

Runaway ascent scenario with new student.
Split between the two, Auto-dump gets rid of gas + student
dumps out of BC, result = twice the gas dumped and student
only has to bother with BC.

or Just drysuit, Auto-dump has to cope with the lot! Student
can press dump and might even tuck and roll, but is unlikely
to get that much more out of it.

I know which one of these is going to work better.

Plus.

Using the suit soley for warmth/squeeze is more of a natural
transition from wet to dry. BC is still being used with
minimal air in the drybag.

Of course as the diving progresses then they might switch to
just drysuit, but in the initial stages its much better for
all the above and more, to use BC first.

TerryH

[matt]

Which method do you use and why?

Neither, I use my lungs as they provide the best performance when it comes to buoyancy CONTROL on O/C. Drysuits and Buoyancy COMPENSATORS are slow and rough by comparison.

Maybe it is something to do with being taught by divers who were venturing underwater before drysuits and ABLJs were about (see Andy Wade's post) but I seem to have a very different view to my peers.

My first pool lesson had me doing fin pivots on the bottom. Breathe in you go up, breathe out you go down. We still do that don't we? My Novice lectures taught me that a drysuit OR BCD could be used to offset buoyancy lost by compression and we still teach that don't we? My first open water lessons routinely included buoyancy checks to make sure I was diving with the minimum of weight making buoyancy adjustment easier. My first dry suit dives were done on just the drysuit and I certainly found that more straightforward than juggling multiple dumps. The exercises included inversions at 6m to make sure that I was not using stupid ammounts of gas to offset over weighting. When the autodump came along I had to slow my ascents to stop the valve being overwhelmed, and my buoyancy control improved across the board as a result. It wasn't until I was diving in BP, wing, twins and stages that I needed to start using the BC. By which time I was sufficiently experienced to make that decision myself.

I now use the BC for rough adjustment, dumping about once every 15 minutes on a 40m to 50m dive and a couple times during ascent. My wing is generally empty by the time I get to 5m and I have held 10 to 20 minute stops as shallow as 2m in good UK conditions. My autodump on the suit is screwed in about a turn. On the odd occassion I need to force gas out my shoulder dump I squeeze it out - easier and quicker than trying to use the purge.

So what is it I am saying. Merely that if you actually follow the progression that BSAC teach, you have a very good chance of accquiring excellent buoyancy skills and never finding yourself on the surface unexpected.

I am quite suprised to see that some of our BSAC instructors want to go the Up/Down button approach. Expedient perhaps, but it only leads to problems later IMVHO. Personally I try to focus on teaching people awareness of all the things which affect buoyancy and how they can manage them. I don't think it is at all important how people control buoyancy, just that they do so.

[paul rosendale]

:=Which method do you use and why?


Hi Steve,

Suit for me. I like to do horizontal trim with frog kick. I find that by using my suit, I can tip forward and let a bit of air migrate to my feet. With my legs bent, it helps keep my feet up and clear of the wreck/silt/Sea fans etc. With using the wing in this position, or slightly heads down, I find the air migrates from one side to the other if you tip on one side to look at something etc. You hear the air rush behind your neck. On Ascent,I find the horizontal position with a slight roll to one side to dump air as required works for me. This can be done very casually with both arms folded. Called "showing off". this way both hands are free, One to hold the shot line, and one free for any other tasks needed. By using the wing and BC, one hand can hold on the shot, the other is engaged in deflating the wing as required, and the third hand is free for any other tasks needed. "THIRD" Ooops. Also as previously mentioned you have 2 expanding air volumes to control. I only want to manage one.
With correct weighting, this has worked well for me for all sorts of diving Inc CCR
It works for me but we're all different creatures

Cheers

Paul

[Andy Wade]

:=Which method do you use and why?

Neither, I use my lungs as they provide the best performance when it comes to buoyancy CONTROL on O/C. Drysuits and Buoyancy COMPENSATORS are slow and rough by comparison.

Maybe it is something to do with being taught by divers who were venturing underwater before drysuits and ABLJs were about (see Andy Wade's post) but I seem to have a very different view to my peers.

My first pool lesson had me doing fin pivots on the bottom. Breathe in you go up, breathe out you go down. We still do that don't we? My Novice lectures taught me that a drysuit OR BCD could be used to offset buoyancy lost by compression and we still teach that don't we? My first open water lessons routinely included buoyancy checks to make sure I was diving with the minimum of weight making buoyancy adjustment easier. My first dry suit dives were done on just the drysuit and I certainly found that more straightforward than juggling multiple dumps. The exercises included inversions at 6m to make sure that I was not using stupid ammounts of gas to offset over weighting. When the autodump came along I had to slow my ascents to stop the valve being overwhelmed, and my buoyancy control improved across the board as a result. It wasn't until I was diving in BP, wing, twins and stages that I needed to start using the BC. By which time I was sufficiently experienced to make that decision myself.

I now use the BC for rough adjustment, dumping about once every 15 minutes on a 40m to 50m dive and a couple times during ascent. My wing is generally empty by the time I get to 5m and I have held 10 to 20 minute stops as shallow as 2m in good UK conditions. My autodump on the suit is screwed in about a turn. On the odd occassion I need to force gas out my shoulder dump I squeeze it out - easier and quicker than trying to use the purge.

So what is it I am saying. Merely that if you actually follow the progression that BSAC teach, you have a very good chance of accquiring excellent buoyancy skills and never finding yourself on the surface unexpected.

I am quite suprised to see that some of our BSAC instructors want to go the Up/Down button approach. Expedient perhaps, but it only leads to problems later IMVHO. Personally I try to focus on teaching people awareness of all the things which affect buoyancy and how they can manage them. I don't think it is at all important how people control buoyancy, just that they do so.

Good points Matt. Nice post. Especially the last point.
We (the forum users) did buoyancy exercises some time ago (around 2001 I think) and I stuck it on the Dive Instruct web site here:



.

[Philip Smith]

Well I can explain the dogma, but not the logic.
Historically the dogma comes from a time when all we had was ABLJ's with no direct feed, and a small emergency cylinder. It gave you support at the surface, and never got used for anything else. Buoyancy control was acheived with precise weighting and within the limits of your lung capacity.

If I may say so Andy, I think you have merged two diving eras here. Precise weighting and breath control hailed from the days before ABLJs -- wetsuits with SLJs, or no buoyancy device other than dumping the weight belt.

If you got it slightly wrong then you really would have had to inflate the jacket with your mouth,

As the name suggests, ABLJs provided adjustable buoyancy and they were used for buoyancy control, even before direct feeds became common. Divers began to weight for neutrality at the surface, rather than at 5m. Underwater oral inflation was routinely taught. Some people used the emergency cylinder for routine inflation, but that was frowned on.

later on direct feeds came in and things got a lot easier for buoyancy control, later still everyone had drysuits and some found it easier to use their drysuit without any lifejacket at all, so all they had was their suit.

I think Variable Volume Dry Suits (VVDS, as they were known at one time) predated ABLJs by some way, although it's probably fair to say that ABLJs were in common use by sport divers before dry suits were. Before direct feeds, dry suits were inflated by mini-cylinder, or even orally (or perhaps not at all).

Anyway, the 'dogma' was based on concerns about controlling two sources of buoyancy. I agree with Matt that, whatever method you use, use it well. The number of DCI cases resulting from errors of buoyancy control is shocking.

Philip Smith

[Andy Wade]

:=Well I can explain the dogma, but not the logic.
:=Historically the dogma comes from a time when all we had was ABLJ's with no direct feed, and a small emergency cylinder. It gave you support at the surface, and never got used for anything else. Buoyancy control was acheived with precise weighting and within the limits of your lung capacity.

If I may say so Andy, I think you have merged two diving eras here. Precise weighting and breath control hailed from the days before ABLJs -- wetsuits with SLJs, or no buoyancy device other than dumping the weight belt.

Possibly, I dived for some time after ABLJ's were introduced before I actually got one, and it had no direct feed and no Automatic Purge valve. We had to hold the button in to breathe into the jacket, and to get a breath from it too. I had a Mark 2 Fenzy (I think)... Mark 3's had the new 'AP' valve and I got one fitted to my Mark 2.
Precise weighting and breath control may have hailed from the days before ABLJ's but it continued for some time afterwards, I said it the way I did because that is when I started diving. So that is what I learned to do. But yeah, SLJ's... I remeber seeing them, not for long after I started diving though, they soon went out of fashion with the Fenzy's and Spiro jackets.
I even remember that these ABLJ's were regarded as a dangerous device by some people at the time. How times change eh?
Later on I dived for years with a Buddy Arctic (the folding one), which never got used for buoyancy control as I used my drysuit instead. It reinforced the use of the drysuit instead of the jacket - for me at least.

:= If you got it slightly wrong then you really would have had to inflate the jacket with your mouth,

As the name suggests, ABLJs provided adjustable buoyancy and they were used for buoyancy control, even before direct feeds became common. Divers began to weight for neutrality at the surface, rather than at 5m. Underwater oral inflation was routinely taught.

Underwater oral inflation, Yes, I did this for my 'G' test IIRC. Out of Porthoustock in Cornwall.

Some people used the emergency cylinder for routine inflation, but that was frowned on.

Never did that, breathed off it though. Still alive to tell the tale. Now that was hard to master. Breathing off the jacket whilst 'trickling air' into the jacket from the emergency cylinder and floating in mid water just inches off the bottom of the pool. Not being allowed to touch the pool bottom. If you could do that, you could do anything.

:=later on direct feeds came in and things got a lot easier for buoyancy control, later still everyone had drysuits and some found it easier to use their drysuit without any lifejacket at all, so all they had was their suit.

I think Variable Volume Dry Suits (VVDS, as they were known at one time) predated ABLJs by some way, although it's probably fair to say that ABLJs were in common use by sport divers before dry suits were. Before direct feeds, dry suits were inflated by mini-cylinder, or even orally (or perhaps not at all).

Yes the old VVDS suits, saw a picture once. But the first drysuit I ever saw was a Poseidon Unisuit with an 'under the crotch' zip, I still have mine in the attic. Can't bear to chuck it away. It had a direct feed. An ex oil rig suit.

Anyway, the 'dogma' was based on concerns about controlling two sources of buoyancy. I agree with Matt that, whatever method you use, use it well. The number of DCI cases resulting from errors of buoyancy control is shocking.

Yes, but I'm not sure it's the same for everyone. I reckon that for some people it's been a case of not using jackets at all, just going from wetsuits to drysuits and not bothering with the ABLJ because they could only afford a drysuit. They then got stuck into 'suit only' buoyancy control, and after being 'forced' to buy an ABLJ, they just wore it and didn't use it for buoyancy control. A bit like me with the Buddy Arctic.
However, YMMV.

[mattbombhead]

:= BC. However, for newbies it does give them two volumes of expanding gas to manage.:=

Important point that.

Runaway ascent scenario with new student.
Split between the two, Auto-dump gets rid of gas + student
dumps out of BC, result = twice the gas dumped and student
only has to bother with BC.

or Just drysuit, Auto-dump has to cope with the lot! Student
can press dump and might even tuck and roll, but is unlikely
to get that much more out of it.

I know which one of these is going to work better.

Plus.

Using the suit soley for warmth/squeeze is more of a natural
transition from wet to dry. BC is still being used with
minimal air in the drybag.

Of course as the diving progresses then they might switch to
just drysuit, but in the initial stages its much better for
all the above and more, to use BC first.

TerryH

That is of course assuming that the suit has an auto dump. Certainly, the suits we have at our club only have a cuff dump.

Personally, when i learned to dive in a dry suit, i was taught to only use my bc on the surface, and dry suit at all other times.

[mattbombhead]

:= BC. However, for newbies it does give them two volumes of expanding gas to manage.:=

Important point that.

Runaway ascent scenario with new student.
Split between the two, Auto-dump gets rid of gas + student
dumps out of BC, result = twice the gas dumped and student
only has to bother with BC.

or Just drysuit, Auto-dump has to cope with the lot! Student
can press dump and might even tuck and roll, but is unlikely
to get that much more out of it.

I know which one of these is going to work better.

Plus.

Using the suit soley for warmth/squeeze is more of a natural
transition from wet to dry. BC is still being used with
minimal air in the drybag.

Of course as the diving progresses then they might switch to
just drysuit, but in the initial stages its much better for
all the above and more, to use BC first.

TerryH

That is of course assuming that the suit has an auto dump. Certainly, the suits we have at our club only have a cuff dump.

Personally, when i learned to dive in a dry suit, i was taught to only use my bc on the surface, and dry suit at all other times.

[Dave]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

Well, I use the wing since I only use a 5mm shorty wetsuit anyway , so no choice :)

When I have used my drysuit, I use the drysuit for dry n warmth and the wing for buoyancy. With air in the drysuit there is too much area for it to move around compared to the small area in a BC. I Find it easier to control

Dave

[Nigel Hewitt]

Personally, when i learned to dive in a dry suit, i was taught to only use my bc on the surface, and dry suit at all other times.

So was I too but I got over it.

Horrifying as it may seem I have to agree with TerryH. I don't think a student with nothing else on their mind has any problem with two sources of buoyancy. Get used to driving two and when one fails coming home on the other is relegated to 'annoyance' rather than incident. Having too much air in a BCD is a problem solved in 3 seconds, too much in a suit, like the 3L over an above that needed to keep you warm so you can go neutral with 3Kgs in your tank jacked up 5 meters, can be far more serious.

I'm a great fan of autodumps. I hear it gurgulling sometimes so I know it's working. I just have to remember to open it when I suit up. The suit reminds me when to put some in so that isn't a problem.

[Kathleen Goddard]

Some people use drysuits for buoyancy control, others us their wing or BCD.

Which method do you use and why?

Hi,

I use my dry suit, when I wear it, for buoancy. I have an auto dump which i open completely as I descend and then turn it off a couple of clicks and i tend to just leave it and it does it's own thing.

Works for me anyway.

[terryh]

Horrifying as it may seem I have to agree with TerryH. I don't think a student with nothing else on their mind has any problem with two sources of buoyancy. Get used to driving two and when one fails coming home on the other is relegated to 'annoyance' rather than incident. Having too much air in a BCD is a problem solved in 3 seconds, too much in a suit, like the 3L over an above that needed to keep you warm so you can go neutral with 3Kgs in your tank jacked up 5 meters, can be far more serious.

I'm a great fan of autodumps. I hear it gurgulling sometimes so I know it's working. I just have to remember to open it when I suit up. The suit reminds me when to put some in so that isn't a problem.


I just see it as a natural progression from a semi or wetsuit.

Cost alone and overseas courses mean that the vast majority
will learn in a semi etc. Soon as conditions dictate a switch
to a drysuit, then it is the same routine as before, but with
minimal air in the suit. Allowing the auto dump to do its thing
means an almost painless transition from semi to dry.

If on the other hand you learned in a drysuit from day one,
with cuff-dump or auto-dump, then ALL the skills are new and
either way (BC or Drybag) would work, but why change the system
when it works fine on the semi-crossovers.

Thats why I always teach BC and drysuit/squeeze/warmth only.

TerryH
PS: In reality we dont do cuff dumps. They are in the bin along
with ABLJ's and autoairs :-)

[Tony Dwyer]

:= BC. However, for newbies it does give
Using the suit soley for warmth/squeeze is more of a natural
transition from wet to dry. BC is still being used with
minimal air in the drybag.

Of course as the diving progresses then they might switch to
just drysuit, but in the initial stages its much better for
all the above and more, to use BC first.

TerryH

You do make a valid point. I used a Gates rubber suit for years until recently. It just wore out and I bought a Northern Diver 'Divemaster' neoprene suit. The new suit is a very good fit and needs just a little air to ease the squeeze. Several of our club members have since bought the same type of suit following training in semi-dry's. They made the transition very easily indeed. Others have bought membrane suits, I reckon they had a slightly more difficult transition.
Concentrating on getting correct weighting seems to be the key element, get it right and the amount of air wandering about is going to be minimal.