Buoyancy
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Joshua Smith
- I've Got Gills
- Posts: 10250
- Joined: Mon Apr 03, 2006 9:32 pm
Buoyancy
OK, so: Tell me everything you can about buoyancy with a CCR. I know it's different with a CCR- you can't empty your lungs to start going down, but.....do you really have to add or subtract gas from your drysuit or wing to go up or down? Do you just seek out square profile dives? I look for that in open circuit diving anyway, but is it more critical on closed circuit? Do you think harder about wasting precious gas in your wing when you want to adjust? I mean, I don't give a second thought to adding a blast of air to my wing right now, but I know that I have been diving a little heavy- is dialing in your trim just that much more critical on a CCR?
Maritime Documentation Society
"To venture into the terrible loneliness, one must have something greater than greed. Love. One needs love for life, for intrigue, for mystery."
"To venture into the terrible loneliness, one must have something greater than greed. Love. One needs love for life, for intrigue, for mystery."
The old saying "OC divers will go over an object and CCR divers will go round it" .
Mel, Curt or John could probably answer this better but here goes:
Think about a perfect hoover on OC, you are still moving up and down when you breathe. On CCR, you aren't moving at all, inhale and the counterlungs collapse and your lungs fill. Exhale your lungs empty and the counterlungs fill. You can actually achieve perfect buoyancy. Want to decend you have to either vent (loop, suit or BC) or forcefully swim down, exhaling just goes into the counterlungs and doesn't do anything. Exhale through your nose to vent loop volume and you'll sink but then you'll be adding more gas to the loop to replace what you vented and get the loop back to the right Po2. Ascend a few feet and you'll feel the loop expand to the point where you will need to vent to maintain min loop volume.
Mel will teach you to keep the loop at minimum volume. Your counterlungs will hold a little more than you need to take a full breath.
Imagine breathing into a paper bag. If it doesn't have quite enough volume to feel your lungs then towards the end of the inhale, you will hit a "wall" where you can't quite get enough air. When you're on the rebreather, you keep the "wall" right at the point where you're getting a comfortable breath. This is min volume, it makes depth changes easier to control and if you need to add Dil or O2 it takes less since the volume is smaller.
Diving the rebreather weight wise is like diving an 80. Given this, you don't have a need for putting alot of air in the wing like you would with double steel tanks. But depth changes are going to require buoyancy adjustments in your suit/BC and your loop. Going up you're adding O2 and going down your adding Dil. The more you do this the more gas you use.
My current setup is to run both my wing and my suit off my Dil bottle. I'm going to change that to running my suit off my 6' bottle cause it leaves my Dil for use where it belongs and it provides more gas available should I need the BOV. Besides once you put Helium in the Dil, you don't want it in the suit anyway.
Hope this helps!
Dave
Mel, Curt or John could probably answer this better but here goes:
Think about a perfect hoover on OC, you are still moving up and down when you breathe. On CCR, you aren't moving at all, inhale and the counterlungs collapse and your lungs fill. Exhale your lungs empty and the counterlungs fill. You can actually achieve perfect buoyancy. Want to decend you have to either vent (loop, suit or BC) or forcefully swim down, exhaling just goes into the counterlungs and doesn't do anything. Exhale through your nose to vent loop volume and you'll sink but then you'll be adding more gas to the loop to replace what you vented and get the loop back to the right Po2. Ascend a few feet and you'll feel the loop expand to the point where you will need to vent to maintain min loop volume.
Mel will teach you to keep the loop at minimum volume. Your counterlungs will hold a little more than you need to take a full breath.
Imagine breathing into a paper bag. If it doesn't have quite enough volume to feel your lungs then towards the end of the inhale, you will hit a "wall" where you can't quite get enough air. When you're on the rebreather, you keep the "wall" right at the point where you're getting a comfortable breath. This is min volume, it makes depth changes easier to control and if you need to add Dil or O2 it takes less since the volume is smaller.
Diving the rebreather weight wise is like diving an 80. Given this, you don't have a need for putting alot of air in the wing like you would with double steel tanks. But depth changes are going to require buoyancy adjustments in your suit/BC and your loop. Going up you're adding O2 and going down your adding Dil. The more you do this the more gas you use.
My current setup is to run both my wing and my suit off my Dil bottle. I'm going to change that to running my suit off my 6' bottle cause it leaves my Dil for use where it belongs and it provides more gas available should I need the BOV. Besides once you put Helium in the Dil, you don't want it in the suit anyway.
Hope this helps!
Dave
I imagine that things get a little more complex on CCR than OC when/if you have to deal with an emergency situation and the task loading and adrenaline result in faster/bigger breaths. Monitoring your PP02, keeping the loop (and thus buoyancy) at the right volume, all while trying to solve whatever problem you might be facing. The muscle memory becomes very important at that point, I imagine.Dmitchell wrote:Imagine breathing into a paper bag. If it doesn't have quite enough volume to feel your lungs then towards the end of the inhale, you will hit a "wall" where you can't quite get enough air. When you're on the rebreather, you keep the "wall" right at the point where you're getting a comfortable breath. This is min volume, it makes depth changes easier to control and if you need to add Dil or O2 it takes less since the volume is smaller.
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Joshua Smith
- I've Got Gills
- Posts: 10250
- Joined: Mon Apr 03, 2006 9:32 pm
Don't worry. We'll find you some muscles, Calvin.Calvin wrote:The muscle memory becomes very important at that point, I imagine.
Maritime Documentation Society
"To venture into the terrible loneliness, one must have something greater than greed. Love. One needs love for life, for intrigue, for mystery."
"To venture into the terrible loneliness, one must have something greater than greed. Love. One needs love for life, for intrigue, for mystery."
You don't need to add/subtract air from your bc/drysuit to go up/down any more than you do on open circuit (or do you exhale to descend? I never did).
It does take effort and practice to lock bouyancy on CCR, just like it does to become 'neutral' on OC. If you're a bit negative or a bit positive you won't be locked. With CCR you need to control bouyancy via loop volume plus drysuit/wing volume.
Square profiles I guess are easier but there's no reason not to do a sliding ascent, in fact it is good to get the practice. Sawtooth profiles indeed waste gas, go around instead where possible. There'd be no waste if you're just ascending.
Diving heavy on a CCR doesn't waste O2 so that shouldn't be a factor compared to diving OC heavy. It may waste a little dil (usually not a limiting factor) depending how you set things up.
Calvin's right -- there's muscle memory, with time you don't notice it. After being on CCR for so long, it is weird coming back to the rare OC dive, I find myself exhaling thru my nose when ascending if I'm not thinking about it.
-Eric
(Evo and Dolphin diver)
It does take effort and practice to lock bouyancy on CCR, just like it does to become 'neutral' on OC. If you're a bit negative or a bit positive you won't be locked. With CCR you need to control bouyancy via loop volume plus drysuit/wing volume.
Square profiles I guess are easier but there's no reason not to do a sliding ascent, in fact it is good to get the practice. Sawtooth profiles indeed waste gas, go around instead where possible. There'd be no waste if you're just ascending.
Diving heavy on a CCR doesn't waste O2 so that shouldn't be a factor compared to diving OC heavy. It may waste a little dil (usually not a limiting factor) depending how you set things up.
Calvin's right -- there's muscle memory, with time you don't notice it. After being on CCR for so long, it is weird coming back to the rare OC dive, I find myself exhaling thru my nose when ascending if I'm not thinking about it.
-Eric
(Evo and Dolphin diver)