Problem with back-inflate bcd

[mnjhuz76]

I had the chance to dive a Zeagle 911 for the first time a couple of weeks ago. Right away I fell in love with the concept and bought one.


I'm still struggeling with one thing, though. To start my descent from the surface, I'm upright in the water left shoulder a little higher the right one, push the deflate button, exhale completely and start sinking. But only like about 2 ft, then my descent stops. In order to get any deeper, I have to flip over and actively swim down. Once I get beyond let's say 12 ft, everything is fine and I have no further problems during the dive. I can even easily stay at shallower depths than 12 ft. It seems as if I just have to get beyond this point once.


Also when ascending at the end of the dive, I'm not popping out of the water. I can maintain a perfectly slow ascend-rate. Once on the surface, trying to get down again would result in the same problem as described above.


Before the 911 I used to dive a jacket-style bcd and didn't have that problem. I was told to add 4 lbs with the 911 which I did (otherwise I probably wouldn't start descending at all).


It feels as if there's some air trapped in the bcd that prevents me from sinking any further during my initial descent. Once at a certain depth the water pressure seems to take care of that problem (at least that's my only explanation for not shooting up to the surface at the end of the dive).


Is there any kind of 'special move' I can make to make sure there is no air trapped in the bcd?


Thanks in advance for your help!

 

[darrenlowjq]

When you say exhale fully, do you have to really empty your bc completely and do a full exhale to initiate a descent? This might indicate that you are underweighted because you should be slightly negative at the start of the dive and nearer to neutral at the end when doing your stop. If this is the case then I would guess that the inability to descend any further would be that you took another breath and became more positively buoyant as a result.

Edit:
I don't know how experienced you are because of the incomplete profile, but might want to pay attention to whether you are unconsciously finning while descending if you descend in a vertical position. If you are able to hold a stop perfectly fine with the current weighting at the end of the dive then this might be a better explanation for your inability to descend.

 

[mnjhuz76]

I learned, that with almost empty cylinder, completely deflated bc and halfway filled lungs I should float with the water surface at eyelevel. Exhaling then should start my descent. This is pretty much given, my descent is slow then, though.


But you are totally right with that breath I might take. When I fully exhale without taking some deep breaths before, I start feeling the urge to breath after about 20 seconds which might be just too short to sink deep enough. I will focus on taking a couple of deep breaths before my next descent, so it takes longer until I have to take my next breath (just tested that at my desk and I can easily stand 40 seconds then).


With about 30 dives since my course, mostly quarry, not too warm (down to low 50s) and very limited sight at times, I consider myself as pretty inexperienced. So I definitely wouldn't rule out finning unconsciously as another factor. I will keep an eye on that as well!


I think this is a good starting point, thanks a lot! I will keep you updated on the results

 

[shortdivemedic]

When I was diving my Balance I would sometimes have trouble getting all the air out and found that if I rolled over and faced upwards toward the surface it would force all the air out . Just my 02 cents

Cheers

 

[darrenlowjq]

If you are diving relatively cold waters, exposure suit compression at depth and the resulting loss of buoyancy might explain why you are able to stay down once you force your way down by finning despite your seeming inability to initiate a descent.

By the way, when I mentioned taking the next breath stopping your descent, I'm not recommending holding the exhale longer. If you are underweighted, the proper solution is to add the weight you need to comfortably descend, but not too much that you sink like a sack of rocks. Diving slightly underweighted can be compensated to a small extent by breathing within the small range of lung volume close to a full exhale but its really uncomfortable if you have to do so for extended periods, speaking from personal experience when I jumped in underweighted previously.

 

[mnjhuz76]

But if I were underweighted and it shows already right at the beginning of the dive, wouldn't I have more and more problems the longer the dive takes and especially towards the end shoot into orbit like a missile?

 

[PACKRMAN]

When I dove a Zeagle Brigade it would trap a little air between the bladder and my body on a giant stride entry. It didn't do it on a back roll entry. I could feel the air release as I transitioned from heads up verticals to slightly head down horizontal descent. It wasn't a problem, just something I had to work around.

 

[mnjhuz76]

Since that (stride) is my main way to get into the water, that's one more thing I will check.

Thanks mate

 

[RJP]

But if I were underweighted and it shows already right at the beginning of the dive, wouldn't I have more and more problems the longer the dive takes ?

No. If you're underweighted, by say 2lbs, at the beginning of the dive... you'll be underweighted by 2lbs at the end of the dive. There's no way for it to "get worse" during the dive unless you dropped lead while you were swimming along. Of course I'm not considering the weight change of the gas that you're using, since that's going to decline during the dive no matter how much lead you have or which BCD you use.

My guess - without seeing you in the water - is that you are slightly underweighted, maybe combined with having some air trapped inside your wetsuit at the beginning of the dive and some slight finning issues. The fact that you don't CURRENTLY pop out of the water at the end tells me you're only slightly light, and that some of that "goes away" during the dive, but that positive buoyancy is replaced by the change in weight of the gas in your tank.

Standard approach: do a proper weight check at the beginning of the next dive, but this time:

1. Flood your wetsuit - including your hood - to get any trapped air out.
2. Cross your ankles to prevent finning
3. As you vent the BCD with your left hand, grab your right shoulder strap with your right to prevent sculling
4. Exhale. Slowly. And fully. And hold it out as long as necessary to see if you sink. (A rapid/forceful exhale here will almost automatically cause you to want to inhale immediately.) However, this should NOT take 20 seconds. If you haven't started to descend after 5 seconds, you're not going to sink.
5. If you don't sink, add a little weight, and try again.
6. Repeat as needed.

The only downside to the standard approach is that it can be frustrating, especially if it takes more than one try. This raises anxiety, exacerbates any finning/sculling issues, and causes your breathing to be more rapid and shallow than you want. The result of this can often be that you inadvertently OVERweight yourself and, being pleased that you've finally descended, you do that dive - and every dive for the rest of your life - overweighted.

The approach I often use with divers who have trouble descending, assuming you're doing shore entries with a buddy who can help you out, is to start the dive by "overweighting" yourself.

I know a few SB stalwarts just had heart attacks, but I don't mean to DO the dive overweighted but rather start your weight check with a few extra small weights. Ideally several small increment - 1 or 2lb - weights. Fully vent your BCD and descend to about 5-10 ft. Not enough to compress your suit, but enough that you can move around to get any trapped air out of your suit. Make sure you've equalized your ears. Generally get comfortable in the water. Get your breathing rate slow and even, get your mask cleared, and hang out for a few minutes.
Obviously, add a little air to your BCD if needed to maintain your 5-10ft depth.

Once you're satisfied that you're comfortable, remove weight. Take a pound off and hand it to your buddy, put it on a platform, etc. And hang out for another minute or two. Vent a little if needed and get back to being comfortable at 5-10ft. No finning, no sculling, just hovering. If you can maintain depth... remove another pound and repeat the process.

Keep doing this step-wise process, remove small increments of weight until you CANNOT maintain depth with your BCD fully vented, no finning, no sculling. At that point, add the last weight you removed BACK to your ballast. Now you're weighted properly!

The thing that I - and most students - like about this approach is that Step 1 of the process is SUCCESS - you've descended! Subsequent iterations are then incremental "refinements" of success... rather than a Trial-Error-Frustration cycle.

If possible, at the end of the dive once you've completed your safety stop, try removing that last weight again and see if you can maintain safety-stop depth with your BCD fully vented, no finning, no sculling. If you descend, remove another pound and see what happens. And another if needed. If you dialed your weighting in properly at the beginning of the dive, you shouldn't be off by much at the end. If you find that you can ditch 2lbs or more at the end of the dive... you were still overweighted by that much at the beginning. If you're only off by an extra pound or so, consider that "extra" pound to be necessary to be properly weighted at the beginning.

Lastly, keep an eye on other configuration changes you might make from one dive to another. I can't tell you how many students are surprised to discover that, yes, something like switching to different thickness hood/gloves/booties or new fins or similar can make a difference. (Oh yeah - and you might be able to deny that your waist is an inch or two larger than it was on your last dive trip... but the water won't!)

 

[mnjhuz76]

Thanks a bunch RJB, this too is very helpful information!

I figured it probably makes sense to do some more pool sessions in order to get this straight using your method. Even if I'm starting overweighted and go down like a rock at least I won't stir up any soil when hitting the bottom

This should get me close to a good starting point for the quarry, I guess.