Acceleration of Ascent/Decent

[Cayman Lover]

Rodale's Scuba Diving has a good blurb this month about how one begins their ascent. Do you kick your way up or inflate a little? I seriously can't remember if this was expressedly taught to me when I got certified. Maybe it was and I just can't remember. The article says if you inflate, the air pocket in your BC will grow much larger than you anticipate as you ascend and accelerate your ascent to potentially dangerous speeds. Counteracting it by letting air out is normal upon any ascent, but starting with too much may cause an over-correction and then you're fighting for neutral buoyancy. By the time you get control, your head may be poking through the water's surface. Not good.

I would imagine that descending would have the same effect (better to kick down than let air out or else you go straight to the bottom as your BC and wetsuit compresses).

Any thoughts on this?

 

[Drew Sailbum]

Begin a descent by deflating your BC until you can initiate a descent by exhaling fully. If you are properly weighted, this will leave a nominal amount of air in your BC. As you descend, add air in small bursts to account for wetsuit compression and compression of air in your BC.

Even if your dive is nominally a square profile you will need to vent a bit of air from your BC a few times during your dive as your cylinder lightens as you use your gas.

To initiate an ascent kick up slightly and/or use lung volume changes. DO NOT add air to ascend! Throughout your ascent you will need to vent air from your BC to account for expanding gas in your BC and re-expansion of your wetsuit. Maintain neutral buoyancy throughout your ascent.

Once on the surface add air to your BC to maintain positive buoyancy.

 

[DA Aquamaster]

Descent: Let the BC do the work.

I like to start vertically in the water and vent air from the BC or wing until I am at about eye level in the water and then just exhale to do the rest. You can then clear your ears, get squared away and then transition to a face down swiming position and continue the descent adding just enough air now and then to keep the descent rate at the desired speed.

Ascent: I will stay very slightly negative and use a gentle kick to come up. It offers more control and ensures I am not going to miss a stop.

The big thing is to develop a feel for the developing trends as you ascend or decend. There is a lag involved in bouyancy adjustment as well as the changes that occur when inhaling and exhaling and you need to develop a feel for how much cahnge is needed and when it is needed.

You also need to be aware of what your limbs are doing and learn to just be in the water without constantly trying to move in the water to develop really preceise bouyancy control. Nothing screws up your bouyancy more than unintentional fin kicks or a hand flopping around.

 

[DandyDon]

I'm sure you and I both were taught better, but - in my case, I think I might have decided to use the "elevator button" anyway. My first ascent from 84 feet got carried away, and I did a bobbing-cork imitation! Good way to hurt oneself - sometimes badly. Now I know to use the Superman positions coming up - one arm up to wave when I break the surface, the other holding onto the release button to let air out of the BC if needed.

:54:

 

[in_cavediver]

Rodale's Scuba Diving has a good blurb this month about how one begins their ascent. Do you kick your way up or inflate a little? I seriously can't remember if this was expressedly taught to me when I got certified. Maybe it was and I just can't remember. The article says if you inflate, the air pocket in your BC will grow much larger than you anticipate as you ascend and accelerate your ascent to potentially dangerous speeds. Counteracting it by letting air out is normal upon any ascent, but starting with too much may cause an over-correction and then you're fighting for neutral buoyancy. By the time you get control, your head may be poking through the water's surface. Not good.

I would imagine that descending would have the same effect (better to kick down than let air out or else you go straight to the bottom as your BC and wetsuit compresses).

Any thoughts on this?

First, get expierence. After a while, you can get neutral quickly and easily. From that, ascending and decending is very easy and requires little manipulation of your BC.

For me, to decend, I dump air to get moving and then add on the way down to maintain control. I can stop whenever I want to but I can drop like a bat out h*** to. I wouldn't want to be positive here.

When I want to ascend, I simply arch my back a bit and increase the residual lung volume to start my ascent (still breathing continuosly though). From there, I dump as needed. I stay horizontal to make the widest surface area (impedes vertical motion) and I can maintian a 30 fpm ascent rate (or slower) easily. I also maintain face to face contact with my buddy.

As for a buoyant ascent, PADI teaches this method in the rescue class for the unconscious diver on the bottom. It is possible to use this and control your ascent rate but it is fairly difficult and not something I would recommend.

As with all of the methods, remember, add and dump is small quantities. You can control small quantities. It's also easier to do all of this when your properly weighted.

Mike

 

[AndrewJD]

The first step to doing a controlled ascent or descent is to be diving a balanced kit. The two critical points for weighting are the begining of a dive at depth with full tanks and the end of the dive at the surface with empty tanks. Ideally you will be able to swim the first up with no air in your BC and you will be neutral for the second. A big factor in the ability to swim up from depth will be the compressability of an exposure suit. This is one of the key advantages of a shell dry suit. It does not compress with depth and its bouyancy should not change from surface to depth. That leaves the weight of your breathing gas as the only variable.

Given a balanced kit: To decend at the begining all you should have to do is empty your BC. You should be negative.

Before ascending you should be neutral. To begin to ascend you take a deep breath. This will raise you in the water column. Once you've begun to rise start breathing normally. Boyle's Law will keep you moving.

To control your acent/decent rate subtract/add air from your BC in short bursts. Also, if you are in a horizontal position the largest cross section of your body will be against the direction that you are going (up or down) and will provide the most drag. This will help to keep your ascent/decent rate low.

Jonathan

 

[Michael Schlink]

You should be neutral throught out the dive, positive if on the surface and neutral the rest of the time. A good way to ascend (and I've put this up before) is as follows;
first "break your initial ascent up into 10' steps. Starting at depth ascend 10 feet, timing your ascent so that it takes AT LEAST 10 seconds to go up 10' preferably 15-20 sec., then go up another 10' at time between each ten feet stop for just a second to make any adjustments and maintain good buddy contact.
When you get to 30' stop and and double check everything again. Now your going to go from 30' to 15' BUT your going to try to take AT LEAST 30 sec. It may seem very slow but that's good, the slower you can go the better.
Then when you get to 15' STOP adjust, buddy check, check air supply, LOOK UP, LISTEN. Now you should be nice and comfortable, NEUTRAL (and preferably horizontal) and making a nice safety stop.
Then after you have completed your safety stop and have signaled your buddy to go up to the surface. LOOK and LISTEN for boats, divers, whale sharks etc. This can be the most dangerous part of your ascent so be careful. DON"T POP UP, but take another 30 sec. to reach the surface.
This may seem a bit tediuos at first but will allow you the time to control your ascent rate, make adjustments as needed and maintain good buddy contact. If you are diving with a computer you won't violate the ascent alarm and you will be helping your buddy with their ascent skills also-Dive Safe-M

 

[MikeFerrara]

When I want to ascend, I simply arch my back a bit and increase the residual lung volume to start my ascent (still breathing continuosly though). From there, I dump as needed. I stay horizontal to make the widest surface area (impedes vertical motion) and I can maintian a 30 fpm ascent rate (or slower) easily. I also maintain face to face contact with my buddy.

Yes. Very simple but they don't teach it.

As for a buoyant ascent, PADI teaches this method in the rescue class for the unconscious diver on the bottom. It is possible to use this and control your ascent rate but it is fairly difficult and not something I would recommend.

An ascent is an ascent is an ascent. It can be a little more awkward controling the buoyancy for two but that's the only difference.

 

[H2Andy]

descent:

i get horizontal, empty my bc, and head on down. once i am past 15 or 20 feet, it
is almost like floating down. i love that feeling. my last few dives i haven't had to put
any air on my BC to stay neutral at depth.

to ascend, i would never put air on my BC. by filling my lungs fuller with each breath,
i can start my ascend. i keept it under control by how much of my lungs i fill up.
my last dive, using 10 lbs, i had a lot of trouble in the last 15 feet of the water column,
with about 700 psi, so i think i might be underweighted.

i use to dive with 17 lbs, and i tell you, the feeling of neutral bouyancy was lost on me.
now with only 12 - 10 lbs, in the last few dives, i have really discovered what it feels
like to be weightless. it's almost effortless to descend and ascend. amazing. you can't describe the feeling.

 

[chrpai]

You should be neutral throught out the dive, positive if on the surface and neutral the rest of the time.

Unless teaching skills to students while your knees are on the sand. :54:

Seriously, keep your bouyancy neutral all the time like he says and there really isn't "start" to the ascent in my mind. You just decide its time to go and vizualize yourself going up just like you would while your swimming around.