Free descent help!

[CuzzA]

No air in BCD. Roll straight back and go down. Immediately start equalizing. Begin adding small puffs into BC about 2/3rds of the way down.

Your mistake was not equalizing sooner. Then of course instead of turning head up to hold your position you added too much gas to the BC. I'd guess you are probably overweight as well.

Here's an example. You can hear the squeak of me equalizing immediately and often.

60 seconds = 100 ft deep.

 

[johndiver999]

I assume you are wearing a full 7 mm suit with hood, gloves boots etc., this provides about 18-30 lbs of lift at the surface.

If you want to do a rapid, "free descent" going down headfirst, you have to keep several things in mind. First, if you were wearing little or no suit,, it would be simple. With your configuration it is not.

You MUST be able to clear your ears quickly and easily and without discomfort in the head down position. If you can't do that, (which can happen on any single day due to congestion etc.) then you are likely to hurt your ears trying this.

First, you should over-pressurize your ears before leaving the surface. A lot of freedivers do this and it may allow your head to descend 10 or 12 feet without any perception of pressure.

When wearing a super thick suit like that, once you kick down to 12 feet or so, you should be quite negative, From this depth, all you have to do is stay vertical, stop kicking for the most part, concentrate on equalization. If you suddenly have a problem with equalization, you must instantly level off flat, getting body in horizontal position which will drastically slow your descent. Then you can try to kick up a few feet, add a small pop of air to the BC, and see how your ears feel. If not perfect, then swim up a little more and try again.

With a full thick suit, you are almost certainly going to be adding a little air at 30 feet, unless you can equalize super fast, your buddy does the same and you have excellent visibility and you know you are not going to crash into anything. It is really not a good idea to place yourself in an extremely negative condition, you are essentially out of control and any ear or gear problems can cascade into a cluster in seconds - so moderation is key.

The simplest way to modulate your descent rate without exertion or messing with the BC excessively, is to change from the vertical head down position to the flat horizontal position. This is what freedivers do (who have no BC to mess with) and who also experience drastic change in buoyancy= especially since their lungs are getting crushed in addition to the suit.

 

[CuzzA]

I will add that unless you're facing fast currents, and need to get to the bottom quick, there's little need for a negative drop.

 

[alex_can_dive]

Thanks for the tips! =) I guess I'll try the horizontal descent sometime. Never even occurred to me that way! (I guess I really didn't have good instructors )

But yeah, I'm not looking to rush my descent in any way - I just wanted to maintain a constant descent rate, which seemed hard.
Now that I think about, this should be automateable - the BCD knows your total weight - it should be able to automatically add/release air to ensure a constant-speed drop. Does this exist yet?

(In case someone came along accusing me of being lazy for asking for a high-tech help, which has happened ,I'm just curious - that's all I write software for a living - this is my dayjob brain thinking

 

[Member002]

Lots of great advice. I feel some of it lacks sufficient detail on how to address it (important for a new diver), and some of the advice is interrelated and only talks about one of the two most common issues. I'll try to put it all together for you. These two issues are separate, but related. Try to tackle both.

Potential issues (you can correct/practice these issues on the same dive day, across two dives):

• You're over weighted
  • Common issue for new divers
  • Amplifies other problems (e.g. you'll troubleshoot a problem but the root cause is still being over-weighted)
    
  • Can be one of the causes for your issue for a few reasons
    • You fully deflate and sink like crazy since you are very negatively buoyant (vs only a little negative when weighted properly)
    • The gas in your BCD compresses as you descend. The more gas you need just to stay neutral, the more dramatic the effect of that compression/expansion has on your buoyancy. So even if you're neutral at some point, after a few feet you'll start to sink/rise faster and faster as the gas compresses or expands. This can cause runaway ascents/descents that can be hard to manage.
  • Solution (fixing this first will make practicing everything else easier):
    • Do this in an easy location where you can take your time. I find easy shore dives (protected cove or lake) are good for this (not a lot of surge, current, etc)
      
    • To get the minimum weight you need to dive, go to a place that has a 12-18ft bottom (15ft is ideal). You can do it off a boat with a good buddy but I prefer a shore dive since you aren't in a rush or anything, and it's easier IMO.
    • At the end of the dive, with around 500 psi, empty all the air our of your BCD. Get it totally empty.
    • If you're in a drysuit dump air until you've got the minimum air to be comfortable and warm.
    • Start removing a little bit of weight at a time (easier if you do this exercise with pouches)
    • After removing weight, wait a second, and see if you can go up and down with your breathing alone
    • If you can't control your buoyancy comfortably (without excessive inhalation), remove more weight
    • Once you hit the point where you feel too light, meaning even slight inhales start to cause you to rise up, add back 1lb at a time until you can breath comfortably while gently rising and falling. That's "neutral".
    • Repeat this exercise every once in a while as your breathing and buoyancy control gets better (you'll likely need less weight).
    • Repeat this exercise when you make big gear changes (drysuit, different mm wetsuit, different tank size/type, etc).
• You're over-relying on your BCD for buoyancy
  • Common issue for new divers
  • Compounds with being overweighed, but still an issue if you're not overweighted
  • Are you frequently are adding and removing air from your BCD during your dive? Do you end your dive by adding air, and begin your descent by rapidly releasing air until you start descending?
  • Solution (easier to practice if you're not overweighted):
    • Do this in an easy location where you can take your time. I find easy shore dives (protected cove or lake) are good for this (not a lot of surge, current, etc)
      
    • Step 1
    • Descend to 10-15 feet normally, however you do it now.
    • At the bottom, get neutral and practice hovering a few feet of the bottom. If staying still is hard, that's ok. Lightly moving forward/in a circle is Ok. Eventually try to do this staying still.
    • "Play" with the air in your lungs and how it impacts your buoyancy. Take a deep full breath and feel yourself rise. Exhale fully and feel yourself sink. Try breathing "full", keeping lungs 40-80% full (don't do this for long, full exhales are important to get rid of CO2). Try breathing "shallow", keeping lungs 20%-60% "full". In both cases you should gently move up and down, but a little more up over time or a little more down over time depending on full/shallow.
    • Once you're comfortable with this, and can manage your buoyancy with a 5ft swing up and down without using your BCD, go to step 2.
    • Step 2
    • Get positively buoyant at the surface.
    • Test your regulators at the surface with five good, full breaths, and watch your SPG (if it drops dramatically or wiggles when breathing check your valve is open all the way). You'll be descending with empty lungs so you don't want a surprise when you try to inhale.
    • At the surface, over a 10-15 foot bottom, release only a little air at a time from your BCD. If you start to sink, add a tiny bit more back in.
    • Each time you release a bit of air, wait a second, and then completely and forcefully exhale air out of your lungs. If you start descending, then don't release any more air from your BCD. And don't take any deep breaths. Leave your lungs empty for a few seconds as you descend. Make sure you aren't kicking sub consciously.
      • Let yourself descend a few feet and then take a slow, shallow breath. If this makes you shoot back up to the surface that's OK. That's why you're practicing.
      • Try again a few times, see if you can descend down to 10-15 ft without releasing any more air from the BCD.
      • Try again, but this time, control your breathing like you did in step 1 and see if you can descend down to 10-15 feet, and then hover, without using your BCD, only your lungs. .
      • When you go deeper, do the same thing for your initial descent from the surface (Just enough air in BCD that you can exhale to descend), only this time add tiny shots of air to the BCD as you descend. But only add enough air so that you can control your buoyancy primarily with your lungs. Exhaling at any time should make you descend, inhaling should make you ascend.
      • At any time you should be able to stop going down by breathing in deeply, or stop rising by exhaling fully.

 

[tursiops]

I just wanted to maintain a constant descent rate, which seemed hard.

It doesn't have to be a constant speed, it just needs to be controlled, and slow enough that your equalizing can keep up with the need to equalize.

Now that I think about, this should be automateable - the BCD knows your total weight - it should be able to automatically add/release air to ensure a constant-speed drop. Does this exist yet?

Yeah, somebody built one some years ago. Total failure. Partly since the goal doesn't involve constant speed.

 

[Dubious]

A little late to this thread but I remember our first outing after being certified we spent one dive just practicing descending and ascending over a 30 foot dive platform. Like most things it just takes practice.