Ascend drills - how many is too many?

[steinbil]

Back when it was the normal ascent rate, there was no safety stop, and in the case of a CESA one will not be doing a stop, so it's a moot point.

When I learned deco and needed to do stops, it was just a matter of slowing and stopping the ascent the same as at 30 fpm. The idea is to maintain neutral buoyancy during the ascent to prevent overshoot. It's a trick, and I learned it.



Hell yeah!

Ascent =/= neutral

 

[steinbil]

Ascent =/= neutral

We’re talking ascent speeds here, so being neutral is not an option. If you mean being neutral when you start the ascent, and at each stop, then yes. However being neutral while ascending doesn‘t work. and the faster your speed of ascent (ascent rate) the less neutral (more positive) you are, which again requires a bigger adjustment to achieve neutral when you reach your stop depth. That leaves less room for error and requires more precision, so I would tend to agree that slower is easier to manage.

 

[Akimbo]

We’re talking ascent speeds here, so being neutral is not an option. If you mean being neutral when you start the ascent, and at each stop, then yes.

Why can't you be neutral through the entire dive with a BC? Doesn't everyone swim up and vent gas along the way? Open circuit divers are never perfectly neutral anyway, just close to neutral about mid-respiration.

 

[steinbil]

Why can't you be neutral through the entire dive with a BC? Doesn't everyone swim up and vent gas along the way? Open circuit divers are never perfectly neutral anyway, just close to neutral about mid-respiration.

I guess it's possible to swim vertically upwards and be continuously neutral by releasing the perfect amount of gas from suit/bc as you ascend, I never even considered it. Sounds like a lot of work, and hard to control with little feedback - how would you even know if you're neutral while finning upwards? Seems easier to start the ascent with a deeper inhale (from neutral at mid-lung volume) and maintain a slightly positive buoyancy and ventilate suit/bc to adjust speed or slow down/stop. At least, that's what I've been taught.

 

[Bob DBF]

Why can't you be neutral through the entire dive with a BC? Doesn't everyone swim up and vent gas along the way? Open circuit divers are never perfectly neutral anyway, just close to neutral about mid-respiration.

Close enough for government work is good, as long as your lungs can make up the difference, you're neutral.

 

[johndiver999]

I guess it's possible to swim vertically upwards and be continuously neutral by releasing the perfect amount of gas from suit/bc as you ascend, I never even considered it. Sounds like a lot of work, and hard to control with little feedback - how would you even know if you're neutral while finning upwards? Seems easier to start the ascent with a deeper inhale (from neutral at mid-lung volume) and maintain a slightly positive buoyancy and ventilate suit/bc to adjust speed or slow down/stop. At least, that's what I've been taught.

What you are described is actually more difficult than a swimming ascent. It is easier (actually requires less skill) to stay just ever so slightly negative and then kick a little harder or softer or not at all during the ascent to regulate the ascent speed.

If a diver always stays on the negative side of the knife edge of neutral, then it is less likely that they will loose control and blow up. If they are swimming up, look at the computer and see it flashing, or start to run into their own ascent bubbles, then theoretically, all they should have to do is stop kicking and their ascent rate should slow or stop. If they stop kicking and they see that they are still ascending, then they can dump a little air and start gently kicking again.

The better a diver gets at this skill, the LESS they have to kick, and eventually as they fully master it, then they will not really be kicking at all and just gently float up using lung volume and BC and suit. when they get to that stage of skill development, then they are staying on the positive side of the neutral knife edge and doing exactly what you are describing.

I think for a real emergency ascent, it might be easier (less task loading) for the rescuer to modulate their kicking effort rather than trying to perfectly fine tune the air volume in 2 BC's and maybe even dry suits too. Plus the rescuer might be confronted with the situation, where the victim tries to help and dumps too much air from their own BC.

 

[Akimbo]

Sounds like a lot of work, and hard to control with little feedback - how would you even know if you're neutral while finning upwards?

Keep in mind that finning at 6" or 150mm per second is REALLY slow. Feedback is easy for open circuit divers, the smallest bubble are moving about twice as fast as you should be.

Drysuits self-vent, especially when vertical. All you have to do is burp you BC now and then. Burp the BC when you are still ascending at the low end of your respiratory cycle and not kicking. 30FPM is too slow to have significant momentum. Glance at your computer every 15 seconds or so and it will tell you to speed up or slow down.

 

[Wibble]

There’s another indication of your ascent rate, how fast you’re winding up your SMB line. A small spool or reel means you’ll wind pretty quickly, more slowly with a larger diameter reel. Listen to the clack clack or the ratchet mechanism.

 

[steinbil]

What you are described is actually more difficult than a swimming ascent. It is easier (actually requires less skill) to stay just ever so slightly negative and then kick a little harder or softer or not at all during the ascent to regulate the ascent speed.

I can‘t really compare, as I never swim to ascend, but I did a midwater ascent with only my instructor as a visual reference on day 2 of my OW class, with a drysuit. Third ever OW dive. It wasn’t that hard. Just the same as controlling your buouyancy at any point of the dive - release gas from BC to slow/stop, vent drysuit if needed (valve is always open, just lift the elbow). Since I was weigthed properly there wasn’t much air in the BC or suit anyways, and I was used to being neutral, not negative.

If a diver always stays on the negative side of the knife edge of neutral, then it is less likely that they will loose control and blow up. If they are swimming up, look at the computer and see it flashing, or start to run into their own ascent bubbles, then theoretically, all they should have to do is stop kicking and their ascent rate should slow or stop. If they stop kicking and they see that they are still ascending, then they can dump a little air and start gently kicking again.

The better a diver gets at this skill, the LESS they have to kick, and eventually as they fully master it, then they will not really be kicking at all and just gently float up using lung volume and BC and suit. when they get to that stage of skill development, then they are staying on the positive side of the neutral knife edge and doing exactly what you are describing.

I’m not convinced. #1 - why teach new divers to be negative instead of being neutral? Especially with the tendency of overweighting, it just seems stressful and a potential hazard. #2 - kicking leads to CO2 buildup, making divers nervous/stressed and all kinds of other problems. #3 - if your swimming upwards you are vertical in the water = less resistance vertically in the water column, less stability, harder to slow down.

I think for a real emergency ascent, it might be easier (less task loading) for the rescuer to modulate their kicking effort rather than trying to perfectly fine tune the air volume in 2 BC's and maybe even dry suits too. Plus the rescuer might be confronted with the situation, where the victim tries to help and dumps too much air from their own BC.

I was taught to empty my own BC and control buouyancy with the victims BC, from behind/on top. So just 1 BC to vent. And by lifting victims left arm I can vent both our drysuits.

EDIT:
sorry to derail the thread, I just remembered what the OP was about, but I guess that came to some kind of conclusion…

 

[jayknight]

EDIT:
sorry to derail the thread, I just remembered what the OP was about, but I guess that came to some kind of conclusion…

Never waste a good opportunity to have a good discussion! Sharing and listening to all these insights is a real learning experience! (If only to learn the difference between ascent and ascend…)