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ricmorte
17-07-2003, 21:22
I read with interest the article on "50 ways to be a better diver" in the August edition of Dive Magazine. I think it would be very good reading for all divers, both new to the sport as well as those with a good many years experience behind them.
Point 13 grabbed my attention: "Work on correct weighting for buoyancy. If you are diving in a drysuit, use only the suit inflator and dump for buoyancy control".
First is the use of the word 'only'. Yes, prescriptive, and miles from the flexible approach to diving techniques we are supposed to engender in students.
Second is the use of the technique itself. OK, I'll come clean: I regard my suit as a means of staying dry and protecting me from cold. So I use just as much air as needed to stay comfortable and avoid compression at depth. I also happen to like a snug fit and like the fact that when trimmed, the BC, weights and air in the drysuit give me a nice position in the water. So yes, I use my BC as my primary buoyancy control, not the suit.
Despite my personal preferences I can see advantages:
No problem when switching to a wet suit - exactly the same buoyancy technique with the BC.
No problem when teaching CBL or AAS ascents: dump air in the suit, make sure the 'casualties' dump arm is raised or the auto dump open and control the ascent on the BC or wing.
In the latter there is no risk either of a student struggling to raise a casualty by controlling the suit buoyancy only to find air leaking out the neck seal and neither going anywhere.
Why, when we have devices engineered specifically for controling buoyancy, do we seem to ignore this fact and still push the line to 'use only the suit inflator and dump' to control buoyancy? I just can't see the sense of it.
If divers want to use their suit to control buoyancy, then fine, it's their choice. But shouldn't we be encouraging students to try different techniques and see what works for them? And, at the training level, isn't teaching so much more effective by keeping it simple, so that what is learnt in the pool transfers seamlessly to open water?
Ric
johnkendall
17-07-2003, 21:53
I read with interest the article on "50 ways to be a better diver" in the August edition of Dive Magazine. I think it would be very good reading for all divers, both new to the sport as well as those with a good many years experience behind them.
Point 13 grabbed my attention: "Work on correct weighting for buoyancy. If you are diving in a drysuit, use only the suit inflator and dump for buoyancy control".
I too noticed this.
First is the use of the word 'only'. Yes, prescriptive, and miles from the flexible approach to diving techniques we are supposed to engender in students.
Second is the use of the technique itself. OK, I'll come clean: I regard my suit as a means of staying dry and protecting me from cold. So I use just as much air as needed to stay comfortable and avoid compression at depth. I also happen to like a snug fit and like the fact that when trimmed, the BC, weights and air in the drysuit give me a nice position in the water. So yes, I use my BC as my primary buoyancy control, not the suit.
Despite my personal preferences I can see advantages:
No problem when switching to a wet suit - exactly the same buoyancy technique with the BC.
No problem when teaching CBL or AAS ascents: dump air in the suit, make sure the 'casualties' dump arm is raised or the auto dump open and control the ascent on the BC or wing.
In the latter there is no risk either of a student struggling to raise a casualty by controlling the suit buoyancy only to find air leaking out the neck seal and neither going anywhere.
Why, when we have devices engineered specifically for controling buoyancy, do we seem to ignore this fact and still push the line to 'use only the suit inflator and dump' to control buoyancy? I just can't see the sense of it.
If divers want to use their suit to control buoyancy, then fine, it's their choice. But shouldn't we be encouraging students to try different techniques and see what works for them? And, at the training level, isn't teaching so much more effective by keeping it simple, so that what is learnt in the pool transfers seamlessly to open water?
You also missed out, that you need to be weighted when empty, so when using larger/more cylinders the bubble of air that you are trying to control at the beginning of the dive is huge (Well, large anyway) So no-one in a twinset is going to try and control all their bouyancy on their suit. The bubble would be unmanageable, and uncomfortable.
This is one of the things in the BSAC Safe Diving Practises that needs removing. Particularly as it invalidates your 3rd Party insurance if you are not sticking ridgidly to the letter of those SDPs
John
Pity one of the 50 was dont EVER leave you buddy alone.
As per "what happend to me"
Supposed Advanced diver leaving a Club/Ocean diver hanging on
at 20m while he goes off for a bit of penetration.
Sad bit is that the author thinks the moral of the story is
follow your training. If she had then she wouldnt have been
there in the first place.
TerryH
> when using larger/more cylinders the bubble of air that you
> are trying to control at the beginning of the dive is huge
> (Well, large anyway) So no-one in a twinset is going to try
> and control all their bouyancy on their suit. The bubble
> would be unmanageable, and uncomfortable.
That does rather depend on the size of your twinset... ;-)
Vic.
> Why, when we have devices engineered specifically for
> controling buoyancy, do we seem to ignore this fact and still
> push the line to 'use only the suit inflator and dump' to
> control buoyancy? I just can't see the sense of it.
Whilst I'm never in favour of closed-mindedness, and so support your general point, I must take issue with this bit.
The drysuit was *also* engineered specifically to control buoyancy, and has been used in this way since long before I started diving. Don't fall into the trap of thinking that, because it does other things as well, it's not about buoyancy control.
Maybe if we called it a "buoyancy suit" we'd get rid of this crazy notion that only a stab jacket can be used for buoyancy...
TBH, I think teaching buoyancy on the suit alone initially is generally quite a good idea; what's important is that we teach "what works, works". Sometimes the suit only should be used. Sometimes the jacket only should be used. Sometimes both. We need to teach our students how to make their own decisions.
Vic.
[Who rarely uses the wing for buoyancy, except on the surface[
ricmorte
18-07-2003, 00:22
> Why, when we have devices engineered specifically for
> controling buoyancy, do we seem to ignore this fact and still
> push the line to 'use only the suit inflator and dump' to
> control buoyancy? I just can't see the sense of it.
Whilst I'm never in favour of closed-mindedness, and so support your general point, I must take issue with this bit.
The drysuit was *also* engineered specifically to control buoyancy, and has been used in this way since long before I started diving. Don't fall into the trap of thinking that, because it does other things as well, it's not about buoyancy control.
OK, good point, but since those early days other devices have come on to the market for doing just this job. That is why I cannot see the logic in continuing to say 'only' the suit inflator/dump should be used.
Maybe if we called it a "buoyancy suit" we'd get rid of this crazy notion that only a stab jacket can be used for buoyancy...
...is this any different from the equally crazy notion that 'only' a suit can be used to control buoyancy?
TBH, I think teaching buoyancy on the suit alone initially is generally quite a good idea; what's important is that we teach "what works, works". Sometimes the suit only should be used. Sometimes the jacket only should be used. Sometimes both. We need to teach our students how to make their own decisions.
Yes, and with your last last points I am fully in agreement. I think it a very good exercise to teach buoyancy using the suit. There may be times, after all, when other buoyancy devices fail and the suit is all you have. The reverse is also true.
If faced with a strong down current, I still wouldn't like to rely on suit buoyancy alone. Point #13 seems to ignore this eventuality altogether. Familiarity with a range of techniques is always a good thing.
Vic.
[Who rarely uses the wing for buoyancy, except on the surface
Interesting. Care to let me know why you prefer this? Do you think the issue is, after all, one of personal preference? Or do you think there are other good reasons for using the suit?
john kendall
18-07-2003, 01:48
> when using larger/more cylinders the bubble of air that you
> are trying to control at the beginning of the dive is huge
> (Well, large anyway) So no-one in a twinset is going to try
> and control all their bouyancy on their suit. The bubble
> would be unmanageable, and uncomfortable.
That does rather depend on the size of your twinset... ;-)
Grrr, Should have guessed you'd have piped up with that!
See ya
John
Interesting. Care to let me know why you prefer this? Do you think the issue is, after all, one of personal preference? Or do you think there are other good reasons for using the suit?
Personally on a single I basically dive the suit but on twins dive the wing. If your properly weighted with a single then you are putting so little air in the BCD its hardly worth the effort. So I tend to have a little in at the begining of a dive but I have dumped it all by about half way through
Pete
First is the use of the word 'only'. Yes, prescriptive, and miles from the flexible approach to diving techniques we are supposed to engender in students.
Completely agree.
Second is the use of the technique itself. OK, I'll come clean: I regard my suit as a means of staying dry and protecting me from cold. So I use just as much air as needed to stay comfortable and avoid compression at depth. I also happen to like a snug fit and like the fact that when trimmed, the BC, weights and air in the drysuit give me a nice position in the water. So yes, I use my BC as my primary buoyancy control, not the suit.
Some jacket BCDs will lift the divers head resulting in underwater doggy paddle. The jacket style was pretty much designed to float a diver upright.
[snip]
Why, when we have devices engineered specifically for controling buoyancy, do we seem to ignore this fact and still push the line to 'use only the suit inflator and dump' to control buoyancy? I just can't see the sense of it.
If we are being pedantic. BCD stands for Buoyancy Compensating Device, not buoyancy control device. The inflate and dump controls are used to compensate for buoyancy change and are pretty crude. Buoyancy Control is achieved with breathing. I prefer the less fashionable trerm stabilising jacket as it is less confusing in this respect. However, if your buoyancy is stable after removing squeeze there is no need to add further gas to the BCD. For many divers wearing membrane suits, 100g thinsulates and carrying 12ltr cylinders, the gas required to adequately remove squeeze is pretty damn close to the volume of gas required to compensate for buoyancy loss. That I guess would be the sense in it.
If divers want to use their suit to control buoyancy, then fine, it's their choice.
AFAIC there is only one effective buoyancy 'control' device...your lungs. Average vital capacity is around 6 to 8 litres. You can breathe that in or out a lot faster than your BC or suit can inflate or dump the same volume. Average tidal volume is only about 0.5 litre so we need to teach people that they have the other 5 or so litres and that is what divers use to control buoyancy.
But shouldn't we be encouraging students to try different techniques and see what works for them? And, at the training level, isn't teaching so much more effective by keeping it simple,
With you here.
so that what is learnt in the pool transfers seamlessly to open water?
AFAIC the object of the pool lesson is to teach safe, effective buoyancy control. Put simply, compensate for depth change and control with breathing. The object is NOT to teach 'this is the up button and this is the down button.'
My attitude to this is that buoyancy must be controlled. In the early stages of OW training the common problems are overweighting and task loading. With the oh so common membrane + 12ltr, fixing the former removes the latter and the trainee is left compensating for buoyancy change solely on the suit.
The arguement the 'BCD was used in the pool so MUST be used in OW' is teaching 'button up, button down' and neglects the fact that buoyancy may not need further compensation once squeeze is removed.
Regards
Matt
Steve Walker
18-07-2003, 13:13
:=Interesting. Care to let me know why you prefer this? Do you think the issue is, after all, one of personal preference? Or do you think there are other good reasons for using the suit?
Personally on a single I basically dive the suit but on twins dive the wing. If your properly weighted with a single then you are putting so little air in the BCD its hardly worth the effort. So I tend to have a little in at the begining of a dive but I have dumped it all by about half way through
Pete
I dive twin 10s and the only time I ever need air in the BC is going over 35m, the rest of the time the air in the suit is more than enough for neutral buoyancy
Regards
Steve
john kendall
18-07-2003, 14:00
:=:=Interesting. Care to let me know why you prefer this? Do you think the issue is, after all, one of personal preference? Or do you think there are other good reasons for using the suit?
:=
:=Personally on a single I basically dive the suit but on twins dive the wing. If your properly weighted with a single then you are putting so little air in the BCD its hardly worth the effort. So I tend to have a little in at the begining of a dive but I have dumped it all by about half way through
:=
:=Pete
I dive twin 10s and the only time I ever need air in the BC is going over 35m, the rest of the time the air in the suit is more than enough for neutral buoyancy
Um, But the bubble in the suit will be the same size regardless of depth. So I don't understand what you mean here.
John
If we are being pedantic. BCD stands for Buoyancy Compensating Device, not buoyancy control device. The inflate and dump controls are used to compensate for buoyancy change and are pretty crude. Buoyancy Control is achieved with breathing. I prefer the less fashionable trerm stabilising jacket as it is less confusing in this respect.
You might prefer it, but it would also be wrong to do so. BCD is a generic term whilst Stab jacket is a specific form of BC. All stabilising jackets are buoyancy compensators but not all BCs are Stab jackets. Wings and ABLJs, for example, are BCDs but they are not Stab Jackets.
Dave
Steve Walker
18-07-2003, 15:10
Um, But the bubble in the suit will be the same size regardless of depth. So I don't understand what you mean here.
John
Nothing much really, just politely disagreeing with the view that:
So no-one in a twinset is going to try and control all their bouyancy on their suit. The bubble would be unmanageable, and uncomfortable
In the bcd v. suit for buoyancy debate it's 'suit only' for me the vast majority of the time as I find that with my current weighting, the amount of air I find to be comfortable to reduce suit squeeze & provide insulation is sufficient to make me neurally buoyant, hence my wing is mostly for redundancy/surface purposes unless I'm adding stage tanks. But But perhaps if I was diving 2x12s the suit might be insufficient.
Cheers
Steve
You might prefer it, but it would also be wrong to do so. BCD is a generic term whilst Stab jacket is a specific form of BC.
Err yes. I have a Hoover made by Electrolux or maybe I don't!
All stabilising jackets are buoyancy compensators but not all BCs are Stab jackets. Wings and ABLJs, for example, are BCDs but they are not Stab Jackets.
I beg to differ in BSAC clubs the BC is a very specific form of stabilising jacket...Buddy Commando :-)
Maybe I can use the term Stab Device..oh no that would be a knife or the more generic Cutting Device ;-)
Now anyone want to discuss the term 'Dived up' surely we 'Dive down' and what about the 'buddy' you hate!
Confused
Matt
Nick Kay
18-07-2003, 17:28
[Who rarely uses the wing for buoyancy, except on the surface]
Perhaps I need a more buoyant drysuit and/or one thats less well-fitting???
Custom Divers Wing, Portland Oceaneering Backplate, Twin 12s, DUI Drysuit, NO weightbelt, negatively buoyant (freshwater, need 2Kg in the sea)
Add twins stages and torch, suit definitely can't cope...
Gordon Archer
18-07-2003, 19:00
>Point 13 grabbed my attention: "Work on correct weighting for >buoyancy. If you are diving in a drysuit, use only the suit >inflator and dump for buoyancy control".
This is correct for training people to dive in dry suits, it works and is safe. Remember the wording is for training not for those of you who have posted about twin set's side cylinders etc etc. That is post graduate stuff and I have no quarrel with you views.
After all you would not be using that sort of gear in a semidry or wet suit, Hmm or would you,:-)
Adrian Kelland
18-07-2003, 20:06
After all you would not be using that sort of gear in a semidry or wet suit, Hmm or would you,:-)
Why not? Twins on the Rosalie Moller seems reasonable to me Gordon. 22deg C and a 3mm wetsuit. Cylinders are likely to be ali's, so overweighting should not be an issue.
Twins steels on a this wetsuit could be intersting though ;-)
Adrian
john kendall
18-07-2003, 20:41
>Point 13 grabbed my attention: "Work on correct weighting for >buoyancy. If you are diving in a drysuit, use only the suit >inflator and dump for buoyancy control".
This is correct for training people to dive in dry suits, it works and is safe.
Yes, this is Good for teaching drysuit use, that way if anything goes wrong in the future, you can control the drysuit.
Remember the wording is for training not for those of you who have posted about twin set's side cylinders etc etc. That is post graduate stuff and I have no quarrel with you views.
Is it? Where does it say that. It says that it is ways to become a better diver. That is something I am always striving to do, yet I don't believe that only using my drysuit for bouyancy would make me a better diver, I think it would make me more of a liability.
After all you would not be using that sort of gear in a semidry or wet suit, Hmm or would you,:-)
Why not? And why does it matter?
If I am on a single tank, and in a drysuit, I use both, take the squeeze off with the suit, and sort out any other bouyancy with the wing. If I am in a wetsuit and a single, I just use the wing. If in a twinset and drysuit, then I will use both.
This is a hang-up to the old days when using ABLJ's and Lifejackets with no direct feed, where the drysuit was the only way of controlling bouyancy. This is no longer the case, and BSAC really should get around to re-thinking this policy.
John
>> [Who rarely uses the wing for buoyancy, except on the surface
>
> Interesting. Care to let me know why you prefer this?
With my dive configuration, my total weight at the end of a dive is almost the same as my total weight at the beginning. So at any stage of the dive, I relieve the squeeze on my suit, and I'm neutral...
> Do you think the issue is, after all, one of personal
> preference?
There is some preference, there are also situations where mandating either is clearly wrong. In my (very particular) situation, for example, it would be *crazy* to require buoyancy control to be performed on the wing; I've also seen rigs with so much gas in them that attempting to do all buoyancy on the suit would be next-to suicidal...
> Or do you think there are other good reasons for using the
> suit?
At the beginning of training, I think it makes loads of sense to use the suit only. But we need to emphasise that this is a training situation - as the student's experience grows, he should be taught the pros and cons of each method, and be able to make his own decisions.
Vic.
> Twin 12s
I use twin 3s...
Vic.
:=After all you would not be using that sort of gear in a semidry or wet suit, Hmm or would you,:-)
Why not? Twins on the Rosalie Moller seems reasonable to me Gordon. 22deg C and a 3mm wetsuit. Cylinders are likely to be ali's, so overweighting should not be an issue.
Twins steels on a this wetsuit could be intersting though ;-)
At Truk lagoon I dived using a 3mm wetsuit and twin 12ltr ali cylinders. What I found was that to finish the dive neutral required a very heavy weightbelt. At Bikini Atoll I dived using the same 3mm wetsuit and twin 13ltr steels but virtually no extra weight.
On a couple occassions I scraped the edge of my wing while attempting to get through passageways which looked wide enough. In the UK I am pretty good at judging the width I need to get through without touching. I put the scrapes down to not being used to having the wing quite that full.
Twin Ali cylinders are pretty buoyant when they are down to 50 bar. Give me steels anyday.
Regards
Matt
Adrian Kelland
19-07-2003, 10:19
> Twin 12s
I use twin 3s...
Vic.
And then carry them in a big yellow box to make it look more impressive ;-)
Adrian
Adrian Kelland
20-07-2003, 10:42
:=:=After all you would not be using that sort of gear in a semidry or wet suit, Hmm or would you,:-)
:=
:=Why not? Twins on the Rosalie Moller seems reasonable to me Gordon. 22deg C and a 3mm wetsuit. Cylinders are likely to be ali's, so overweighting should not be an issue.
:=
:=Twins steels on a this wetsuit could be intersting though ;-)
At Truk lagoon I dived using a 3mm wetsuit and twin 12ltr ali cylinders. What I found was that to finish the dive neutral required a very heavy weightbelt. At Bikini Atoll I dived using the same 3mm wetsuit and twin 13ltr steels but virtually no extra weight.
In the UK I am pretty good at judging the width I need to get through without touching. I put the scrapes down to not being used to having the wing quite that full.
Such inflation might be a symtom of overweighting.
Twin Ali cylinders are pretty buoyant when they are down to 50 bar. Give me steels anyday.
Did you do any weighting/trim tests with the alis? A weight belted on the cylindersmay have made all the difference.
Regards
Matt
All I can say I have used twin alis with a 1mm skin with no problems re the alis floating.
Adrian
Gordon Archer
21-07-2003, 19:30
If I am on a single tank, and in a drysuit, I use both, take the squeeze off with the suit, and sort out any other bouyancy with the wing.
On every occassion I have met divers who have had bouyancy problems thay have been trying to control their bouyancy in precisly the way you described.
Take them back into the pool back to basics, follow the BSAC recommended dry suit course and they have no more problems, and all have come back and said how much more they now enjoy their diving.
This is a hang-up to the old days when using ABLJ's and Lifejackets with no direct feed, where the drysuit was the only way of controlling bouyancy. This is no longer the case, and BSAC really should get around to re-thinking this policy.
Well this might be might be your opinion but from an instructional point, BSAC must not change this policy, I personally do not think this is a hang-up from the old ABLJ days, which I did train on. It is a matter of safe practice and that fact cannot be ignored.
Trying to control two sources of air is a recipe for disaster, and on that point also your method cannot be taught. (IMHO):-)
As to the twin set theory, I can only think you are grossly over weighted when kitted like this to require massive lift from a wing(I have nothing against wings).
As an extra tank would displace a larger volume than the equivalent dry weight of lead, it would be simply a case of removing the equivalent of the weight of the tank in water, from the lead around your waist. Thus returning to the same starting point bouyancy(Fully kitted up weight v volume) As the single setup and therefore the dry suit works the same. Doesn't it?
Such inflation might be a symtom of overweighting.
Well yes. If I want to be neutral at the end of the dive with empty cylinders I need to be negative at the start of the dive with full cylinders. Twin Alis are buoyant so I don't just have the weight of the air in the twins but also the additional weight required to sink the empty cylinders.
In the UK my dry suit holds some of the volume required to offset the initial overweighting. In a wetsuit that volume has to go in the wing hence greater inflation.
:=Twin Ali cylinders are pretty buoyant when they are down to 50 bar. Give me steels anyday.
Did you do any weighting/trim tests with the alis? A weight belted on the cylindersmay have made all the difference.
Yes I played around a bit on the first couple days. Adding a kilo to the back of each tank corrected the trim on stops but kicked my head up for the rest of the dive. I decided bum in the air on stops was the lesser of the two evils.
All I can say I have used twin alis with a 1mm skin with no problems re the alis floating.
Apart from my buddy and myself there were two other guys from Seattle who also dive twin steels at home. Everyone agreed that the Alis were a comparitive pain. Not a problem as such just not particularly comfortable.
Regards
Matt
On every occassion I have met divers who have had bouyancy problems thay have been trying to control their bouyancy in precisly the way you described.
Many inexperienced divers I see who appear to struggle are trying to balance air in both drysuit and BCD. Overweighting and breathing technique are also favourites though.
Take them back into the pool back to basics, follow the BSAC recommended dry suit course and they have no more problems, and all have come back and said how much more they now enjoy their diving.
I don't usually bother going back to the pool. I suggest they try using just the suit and then we review which method they prefer and why that might be. Divers in membrane suits always prefer just the suit, so far. Divers in neoprene split 50/50.
Well this might be might be your opinion but from an instructional point, BSAC must not change this policy, I personally do not think this is a hang-up from the old ABLJ days, which I did train on. It is a matter of safe practice and that fact cannot be ignored.
Trying to control two sources of air is a recipe for disaster, and on that point also your method cannot be taught. (IMHO):-)
Disagree (strongly). It may be more complicated, but it should be within the abillty of any competant diver. I can understand the inexperienced having trouble. There are so many new things for them to deal with that task loading is a very important issue. To be considered competant (safe), proficient use of two buoyancy devices should not be outside your capacity.
IMHO I don't care how diver's control buoyancy, but IT MUST be controlled. If they want to use drysuit and BCD then thats OK, but I will not sign them off until buoyancy is controlled.
As to the twin set theory, I can only think you are grossly over weighted when kitted like this to require massive lift from a wing(I have nothing against wings).
Oh please don't invite the pedants. Some wings have less lift than a Buddy Commando.
As an extra tank would displace a larger volume than the equivalent dry weight of lead, it would be simply a case of removing the equivalent of the weight of the tank in water, from the lead around your waist. Thus returning to the same starting point bouyancy(Fully kitted up weight v volume) As the single setup and therefore the dry suit works the same. Doesn't it?
See my earlier post.
You have neglected the weight of air in the cylinders. A single 12ltr changes buoyancy by a little over 3Kg from full to empty, twin 12s change by 6Kg. 3Kg is comfortably within the range of your lungs, 6Kg is marginal. So yes at the start of a dive in twin 12s you are significantly overweighted and you know it. If your carrying additional decompression cylinders the situation is even worse.
Regards
Matt
john kendall
22-07-2003, 00:04
:=
:=If I am on a single tank, and in a drysuit, I use both, take the squeeze off with the suit, and sort out any other bouyancy with the wing.
:=
:=
On every occassion I have met divers who have had bouyancy problems thay have been trying to control their bouyancy in precisly the way you described.
Take them back into the pool back to basics, follow the BSAC recommended dry suit course and they have no more problems, and all have come back and said how much more they now enjoy their diving.
Yes, At the basic level, and in order to teach it, then just use the Drysuit, It is only 1 source of bouyancy, and will teach how to control it. Control is the key. However once under control, then you can use both. It is not Hard, It is not difficult, it is not dangerous, but you need the control first.
:=
:=This is a hang-up to the old days when using ABLJ's and Lifejackets with no direct feed, where the drysuit was the only way of controlling bouyancy. This is no longer the case, and BSAC really should get around to re-thinking this policy.
:=
Well this might be might be your opinion but from an instructional point, BSAC must not change this policy, I personally do not think this is a hang-up from the old ABLJ days, which I did train on. It is a matter of safe practice and that fact cannot be ignored.
Not saying that Drysuit only is not a useful step in learning, but once beyond that, you should have the flexibility to use either/both.
Particularly as your 3rd Party insurance is only valid if you are diving within BSAC's SDPs, so anyone using their wing/bc for bouyancy, is technically outside their insurance.
Trying to control two sources of air is a recipe for disaster, and on that point also your method cannot be taught. (IMHO):-)
No its not. It is not possible to teach it in one step, however with Small steps (As taught in the IFC etc) it is totally possible to teach someone to use both.
As to the twin set theory, I can only think you are grossly over weighted when kitted like this to require massive lift from a wing(I have nothing against wings).
As an extra tank would displace a larger volume than the equivalent dry weight of lead, it would be simply a case of removing the equivalent of the weight of the tank in water, from the lead around your waist. Thus returning to the same starting point bouyancy(Fully kitted up weight v volume) As the single setup and therefore the dry suit works the same. Doesn't it?
Nope. You have forgotten the weight of the Gas in the cylinders.
In a single you need to start the dive about 3.5kgs negative, in order to be neutral with empty tanks. In a twinset you need to be 7kgs Negative. And once you start adding a couple of stages all that gas needs to be allowed for. This all adds up to a Massive bubble of air to get neutral at the beginning of the dive. Far in excess of what is comfortable in the Drysuit.
Now it is possible to dive with that big a bubble, but it is not comfortable, and I would not consider it safe. So you put the majority of the bubble in the wing, and Then nice and comfortable, as well as less of an issue if you do wish to keep your legs out of the silt.
John
edward haynes
23-07-2003, 08:01
My exact thoughts when I read the article.
Edward
Pity one of the 50 was dont EVER leave you buddy alone.
As per "what happend to me"
Supposed Advanced diver leaving a Club/Ocean diver hanging on
at 20m while he goes off for a bit of penetration.
Sad bit is that the author thinks the moral of the story is
follow your training. If she had then she wouldnt have been
there in the first place.
TerryH
Steve Walker
23-07-2003, 10:47
My exact thoughts when I read the article.
Edward
:=Pity one of the 50 was dont EVER leave you buddy alone.
:=As per "what happend to me"
:=
:=Supposed Advanced diver leaving a Club/Ocean diver hanging on
:=at 20m while he goes off for a bit of penetration.
:=
:=Sad bit is that the author thinks the moral of the story is
:=follow your training. If she had then she wouldnt have been
:=there in the first place.
:=
:=TerryH
IIRC the dive Marshal was aware of the dive plan and gave it a thubs up - slapped wrists all round!
Andy Wade
23-07-2003, 11:09
:=My exact thoughts when I read the article.
:=
:=Edward
:=
:=:=Pity one of the 50 was dont EVER leave you buddy alone.
:=:=As per "what happend to me"
:=:=
:=:=Supposed Advanced diver leaving a Club/Ocean diver hanging on
:=:=at 20m while he goes off for a bit of penetration.
:=:=
:=:=Sad bit is that the author thinks the moral of the story is
:=:=follow your training. If she had then she wouldnt have been
:=:=there in the first place.
:=:=
:=:=TerryH
IIRC the dive Marshal was aware of the dive plan and gave it a thubs up - slapped wrists all round!
It looks like they were sliding down the slope of the incident pit even before they got into the water.
.
Nick Kay
23-07-2003, 18:42
Sad bit is that the author thinks the moral of the story is
follow your training. If she had then she wouldnt have been
there in the first place.
I thought she was saying the following:
Don't rely on your buddy. I believe she's concerned that too many divers are reliant on their buddy to get them out of trouble and that divers should therefore practice self-reliance.
I could also read into the story that she's saying "s*** happens"
:=Sad bit is that the author thinks the moral of the story is
:=follow your training. If she had then she wouldnt have been
:=there in the first place.
I thought she was saying the following:
Don't rely on your buddy. I believe she's concerned that too many divers are reliant on their buddy to get them out of trouble and that divers should therefore practice self-reliance.
Yeah you could draw that conclusion.
Mind you when you go into the water with the deliberate intention of seperating from your buddy there is no point in having a buddy in the first place.
Leaving someone on their own, especially a less experienced diver like this, is frankly inexcusable.
The problem was not that the buddy system is a bad thing, it's that it wasn't being used properly.
I could also read into the story that she's saying "s*** happens"
It does happen of course but in this case it wasn't anything to do with "s*** happening" and everything to do with poor planning.
John Williams
27-07-2003, 18:15
Um, But the bubble in the suit will be the same size regardless of depth. So I don't understand what you mean here.
John
If he is diving in a membrane suit then I'd agree with you.
However if he's diving in a neoprene suit (particularly if it's not a crushed neoprene suit) then the bubble has to be enlargeed to compensate for the buoyancy lost through compression of the bubbles in the suit material at depth.
This is one reason why I dive in a membrane suit - I don't need to introduc excess air into it to compensate for this phenomenon at depth.
John
I thought she was saying the following:
Don't rely on your buddy. I believe she's concerned that too many divers are reliant on their buddy to get them out of trouble and that divers should therefore practice self-reliance.
I could also read into the story that she's saying "s*** happens"
Trouble is that both those responses ignore the obvious fact
that she shouldnt have been there in the first place.
I can think of absolutley no circumstances whatsover
where a greenhorn Club diver is left alone. She may have an
excuse through lack of knowledge/experience, but the Advanced
diver and DM do not.
TerryH
Nick Kay
28-07-2003, 00:38
I can think of absolutley no circumstances whatsover
where a greenhorn Club diver is left alone. She may have an
excuse through lack of knowledge/experience, but the Advanced
diver and DM do not.
Absolutely and she's extremely safety conscious and wouldn't (as an experienced diver, OWI and DO) countenance such a situation.
However, she can look back to when she started and use that experience to point out to others that
a) Don't rely on your buddy
b) This was a stupid (understatement) position in which to have been left...
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