Decompression Attitude

[julian.carroll]

Hi,

I have heard a fair few people say that one should decompress horizontally, but I can't find any good information about it. The argument presented to me for decompressing horizontally is that there is no (or at least little) pressure gradient across the body.

On the other hand, I have also heard people say that it is sensible to decompress vertically so that you can fin gently to maintain your stop depth. The thinking here is that finning keeps you warm (hence increases blood circulation around the extremities) and forces you to breathe harder (helping off-gassing).

I would be interested to hear what comments others have. Does the pressure on the body matter, or is it just the pressure of the gas we are breathing? For those who would recommend horizontal decompression, how can one avoid the tendency of the SMB to pull one into an upright attitude?

Thanks,

Julian

[weazelz]

For those who would recommend horizontal decompression, how can one avoid the tendency of the SMB to pull one into an upright attitude?

if you are properly trimmed for a hoizontal attitude & properly neutrally buoyant - ie not slightly negative & hanging off the SMB - then it will not pull you upright

[Richard Whitcombe]

On the other hand, I have also heard people say that it is sensible to decompress vertically so that you can fin gently to maintain your stop depth.

Surely the whole point of neutral buoyancy is you can hold a depth without having to fun. Meaning less gas usage, less effort. Gentle horizontal swimming is easy enough under an SMB if you want to get some circulation and warmth.

[MattS]

Hi,

I have heard a fair few people say that one should decompress horizontally, but I can't find any good information about it. The argument presented to me for decompressing horizontally is that there is no (or at least little) pressure gradient across the body.

On the other hand, I have also heard people say that it is sensible to decompress vertically so that you can fin gently to maintain your stop depth. The thinking here is that finning keeps you warm (hence increases blood circulation around the extremities) and forces you to breathe harder (helping off-gassing).I have had a few heated discussions over this one (a bit sad I know). An argument is that the pressure differential over the length of the lungs is going to make bugger all difference and so there is nothing wrong with vertical decompression. Another argument is that the pressure differential across the whoe body when vertical increases blood pressure in the lower torso and legs, so increases the heart's workload.

Breathing harder while offgassing is not such a good idea. On scuba you breathe to excrete CO2. Constantly finning, needing to breathe more, means you are generating increased CO2 and although there is no catagoric proof, it probably interferes with offgassing overall. Ideally you want to be gently exercising extremeties to promote blood flow in capilaries.

I would be interested to hear what comments others have. Does the pressure on the body matter, or is it just the pressure of the gas we are breathing?If nothing else a horizontal attitude will put your chest at the same height as your computer/depth guage.

For those who would recommend horizontal decompression, how can one avoid the tendency of the SMB to pull one into an upright attitude?If the SMB is pulling you upright your are negative and using the SMB as a crutch. When you are neutral you can drop your reel without changing depth. I spend a lot of my decompression time floating with the reel a few inches in front of me (not holding onto it).

[Paul Oliver]

Being horizontal and finning is a sure indicator of poor buoyancy control, and off of Dover where we return to the shot it has a good chance of getting you an irritated poke as we have 12 divers trying to hold the 6m point on the shotline, with some clown kicking us as they do not have their buoyancy controlled :angry:

I deco horizontal and gently fin to keep my blood flowing, it is by far the most comfortable position.

When using a DSMB its the same, if you are hanging off of it your buoyancy is generally poor, try floating horizontally next to it, much more comfortable and all of you and your puter are at the same depth.

Personally i prefer to swim around mine, it keeps me alert and active, promotes blood flow and helps me practice my buoyancy skills.

[tony J]

how can one avoid the tendency of the SMB to pull one into an upright attitude?

what I do for the shallower stops... (I guess it does not work on a spool)

Disconnect the SMB from you (if attached ) and let go of it.

Then use it as a shot line , lie horizonatally and loop your fingers around the line so that you are not pulling on it.

In fact I often have both arms out in front of me in a diamond - so rather than it pulling me up I'm just floating - or occasionally pushing down on it.

When you change depth you just reel in another 3m.

This is the same way I use a drop line.

The smb should not have any affect on ones buoyancy - often people use it to pull themselves up.

Tony

[Nigel Hewitt]

I like to have a little tension in the string so I know I'm not rising but we're talking about enough to feel the line not a pull me off horizontal.

For long hangs I tend to roll onto my back and hold the reel near my tummy. I find that a very comfortable way to pass one of the more boring bits of diving.

I hate people who fin on stops. They just flap off into the distance oblivious to you. I used to be good and follow them but now I just let them go. Too often they don't realise it was them that swam away and ask silly questions like "where did you go?" back on the boat.

[Richard Whitcombe]

what I do for the shallower stops... (I guess it does not work on a spool)

Works fine on a spool. You can lock it off with the boltsnap just as you do a reel.

[Steve Pearson]

what I do for the shallower stops... (I guess it does not work on a spool)

Disconnect the SMB from you (if attached ) and let go of it.

Tony :rolleyes:

[allanswallace]

Gentle excercise is a good idea, but based on the way that tables were calculated in the first place (eg, with a built in safety margin based on error) i don't think it will make a great difference what your orientation is. especially if you are extremely short - if you are a giant it will make more of a difference.

I personally, prefer horizontal, gentle finning to retaing pointing towards my buddy so they can see me, and I them, and with a little bit of weight down on the smb/dsmb - in order to A> keep the line taught, and B> keep the smb/dsmb vertical, for ease of visibility from the surface / shore / boat.

Just my two-penneth..