Changing levels during ascent

[elan]

We were working today on perfecting the buoyancy while changing the depth and I just wanted to ask other divers how they change the levels in terms of operating their buoyancy devices when changing thenm at different depth. We were mostly working at 40 - 30 ft depth coming back and forth between the 2. Some time ago I had to dump air from the wing/DS whilw changing from 40 to 30 and back but today I was fairly comfortable without touching the BC/DS. Yet it is more difficult at this moment to do it from 30 to 20 or from 20 to 10.

I was diving LP108s full with nitrox which make roughly 18lb of gas in the wing and my suit is roughly 24lb buoyant.


I was doing some calculations and what I got is:

If the depth changes from 40 to 30 ft the pressure changes about 0.18 times so the air will expand to provide another 8lb of lift so if one starts ascend with near full lungs and exhales on the way up even without dumping air it is marginally possible to manage that. If one dumps air form the suit only the swing to compensate would be ideally less than 4lbs which is doable.


One guy told me he starts the ascend and then starts dumping the suit and the wing half way.

So how do you, guys, operate your dumps while changing the levels ?

 

[TSandM]

Well, the strategy I've worked out for myself is that the wing is easier to dump than the suit, so I dump the wing until there's nothing left there to vent, and then I start dumping the suit (which by that time has expanded to where it's pretty trivial to get gas out of it).

A lot of the time, diving a single tank, I have no air in the wing at all, anyway; I've moved to putting as much gas in the suit as I can keep there, to stay as warm as possible.

 

[Blackwood]

I have a generic "this is the right amount of gas in the suit" feel, and seek to maintain that (+/- depending on water temperature).

During ascent, I inhale deeply and raise my arm to allow the suit to dump. Somewhere along the way, I dump the the wing. I can't say half way, 3/4 or anything specific; I dump when I need to.

During descent, I exhale deeply and add gas to the wing to control rate while adding to the suit for comfort.

 

[DiverLaura]

Stay ahead of the ball... if one gas bubble is harder for you to dump than another, practice

I consider the gas in my suit for lofting purposes only. What this means on ascent is always maintaining control over that larger and harder to control bubble.

One way i find myself doing this is as follows.

Ascent begins. I dump gas from my suit and if needed put a bit of gas in the wing to maintain neutral or just 'swim gently up'. (its a bit counterintuitive, as if i've been diving tanks with big swing weight i'll have probably let some gas out)
as i continue up, i can then feather dump the wing... BEFORE I feel the suit getting 'fluffy' i'll repeat the procedure of emptying all the gas that will leave the suit, TOTALLY BREAKING TRIM if need be... again, since wing is easier/faster to dump, i'll maintain more gas in there than i will as a suit bubble. I'm not squeezing myself mind you, that is rather hard to do on ascent unless you ascend a bit and then descend. once i'm in a stable position at a depth that i'm going to remain at for a while (say a deco stop?), i may leave a little more gas in the suit, but generally its just enough to be comfortable, but not increase the bubble shift in the suit. If my undergarments are appropriate for the dive i've planned (I run with all sorts of random variations, as i've learned through time that there is no perfect undergarment) then i should not need to overinflate them. If you are used to diving very squeezed as an alternative to managing suit bubble, then you will likely find some comfort in adding a bit more gas for warmth, but if you are already diving 'lofted' the gain is sometimes not worth the annoyance factor.

What is this lofted you might ask? Well... if you've taken fundies from Bob Sherwood, you've likely heard all this already. I'll try to explain it to the best of my ability, but Bob, if you're around, you might want to correct any misinterpretations

fill your suit with gas (exhaust valve closed or mostly closed), laying face down in water with 2nd stage in mouth... wiggle your arms, stretch them over your head for a valve drill (I incorporate a flow check here) stretch out your legs, kind of kick your legs 'out' a couple times, in almost a marching position, stretch your body side to side with arms out in front on surface of water like you are doing a good side stretch... get your suit all 'stretched out' and unbunched for optimum mobility (you'll kind of feel the crotch of the suit back up where its supposed to be cause likely your pockets pulled things down, and you'll have better mobility of your legs for back kicking and such)

OK, now open the valve and bring yourself upright. You'll feel the gas escaping and your suit kind of hugging your legs... not shrinkwrapping, just hugging. Kind of hunker down in the water raising the left shoulder/elbow a bit (with hands down in water) letting the gas out of upper body.

feel that? now if you go horizontal, that feeling is 'lofted'. as you descend down, just as your suit starts hugging (not squeezing) add a touch of gas.. this is all about small moves... every 10' or so (more frequently in the beginning, less frequently as i descend) i put gas in the BCD to maintain neutral with my suit lofted.

slight exception: I learned the hard way in Florida that a lofted suit will try to blow your drysuit boots off if you are doing a head first descent into a cave. The only way i found to get around this was descend with basically no gas in suit, only enough to maintain some mobility but not blow your boots off, using BCD for buoyancy control Then sort the squeeze and lofting out once you've completed the entry. There are probably more elegant ways of dealing with this issue, but i've only done a tiny bit of cave so don't know many of the tricks

So basically what Blackwood said

sorry about the rambling on... if the OP's question was about a BC only, then just ignore all the stuff about drysuits, but do try to stay ahead of the ball and make small adjustments as opposed to big ones.

if you are correctly lofted and weighted, then if you start to ascend and get 'lighter' than you can control with lung volume alone, a few frog kicks should just kick you back into place as opposed to doing a big gas dump and then overshooting on the downswing as you re-reach target depth and having to put more gas back into the system.

but never ever hesitate to stretch your legs out a bit and break trim to get that gas out of the suit if you need to.

Team before Trim... Good buoyancy control helps Team. So, Buoyancy before Trim . Do not sacrifice buoyancy for looking pretty as you float to the surface without your team, in perfect trim

 

[rjack321]

Often I see people venting the wing and inadvertently venting the suit at the same time. Close down your suit valve a bit esp. if you are trying to conserve warm suit gas for later. Otherwise try alternating which one you're venting until you get the feel for each. With a single tank (even a big one) you don't have that much gas you will need to release so it can be one or the other when you are just practicing and the tank is maximally negative.

For me in real life, I am always trying to get rid of wing gas first. To conserve heat and avoid having to re-inflate my suit and warm that new suit gas up again.

 

[TSandM]

Laura has a good point -- this is all environment-dependent. If you are cave diving, the contour of the cave may require some "non-traditional" orientations (if the cave slopes down, YOU slope down) and running a lot of gas in the suit can be extremely uncomfortable to unmanageable.

In open water, you can run as much gas in the suit as you want, and the strategy I described (and rjack confirmed) works just fine.

 

[cfenton]

I manage ascents exactly how Blackwood describes. The key being to stay ahead of the ball.

 

[lamont]

i tend to find the drysuit dump is much less fussy, so i tend to use that for 'fine' control, and i'll dump that maybe 3 or 4 times as i'm moving between stops. the wing dump i tend to use once as i'm moving between stops. i've got no particular pattern as to when i dump the wing -- might be near the start, the middle or the end of the move depending on how it feels. generally i'm dumping out the wing as the drysuit starts to feel too squeezed (or i start to feel too light with the drysuit properly lofted). if i'm leaving the stop a bit light, i'll dump out of the wing soon, if i haven't dumped out of the wing during a move i'll do that towards then end of coming into the stop.

a lot of this is just an extension of being able to move gas from wing to drysuit and vice versa at any time. just instead of dumping one and inflating the other, you preferentially dump one and let the other one inflate as you ascend -- which shifts buoyancy. so if you're squeezed and cold, just dump out of the wing a bit more.

and when it comes to 20 foot to the surface it gets a lot more fiddly with a lot more dumping out both.

i also tend to alternate a bit between butt dump and corrugated hose. i think i do tend to slightly favor the butt dump for style points, but if the wing is getting light its easier to get all the gas out by dumping the corrugated hose. its also easier to dump both the wing and drysuit at the same time by going head up and dumping which avoids the rocking-forward-and-back issue if you're trying to dump both essentially at the same time.

 

[nadwidny]

I use my wing as little as possible and tend to put most gas in my suit. Gas in the wing does absolutely zero to help keep me warm and it's easier to dump suit gas while scootering than wing gas. There are some DIR folks out there that advocate the shink-wrap method of diving dry. I don't get this. Gas in the suit equals warmth. If you need gas to adjust your bouyancy, why not add it to a place that does double duty?

I must add that when I went to a dry suit the style in my area for drysuit diving was backplate with no BC (just the suit for bouyancy control) and dove that way for about 5 years or so. So I am quite used to using the suit for bouyancy control.

 

[lamont]

uhm, there's a happy medium between shrink-wrapped and cold, and entirely using the suit for buoyancy control. believe me, i like to use all the thermal gear that i paid for, but beyond a certain point the bubble isn't doing much for you thermally and its a pain to manage and that gas sits better in the wing.

and, yes, for scootering i run more gas in the suit to kick my feet up and get more streamlined in the water, and you seem to need a bigger bubble when you're scootering to keep warm (gets pushed towards your feet so you need more to loft your core?)