Buoyancy/weighting questions from a very new diver.

[Hypno-toad]

I am a brand spanking new diver (just logged in my 3rd and 4th post-OW-certification dives yesterday morning) so please excuse the severe idiot newbie-ness. I have a couple questions about buoyancy and weighting. I feel like I am starting to get the hang of this whole diving thing, and while I have never (in my vast 4 dives) not had a blast, I am striving to better myself as a diver. I know most of that will come with just diving and diving and diving, but I figured I'd tap into the knowledge here as well.

I did two dives yesterday morning and I went with a couple of divers who were with with me on my very first dive. They noted marked improvement and one even commented that I seemed to be "getting buoyancy down pat". I commented that I felt I might be slightly overweighted as my tendancy was to sink down when we were not moving and I had a hard time hovering. When moving, no, I have little problem controlling my position in the water, but staying off the bottom while stopping is much harder. I am not so heavy that I drop like a rock, but often a little push off the bottom is required. I put a couple pinches of air in my BCD and that helped, but it seems like I should have an easier time with it. The very experienced group I dove with noted no real problems and seemed surprised when I said I felt over-weighted.

Here is where I get confused (enter the inexperience). My initial descent is not at all rapid and I find myself doing the "upwards paddle" with my arms to try and drop with my group/buddy as they tend to descend much easier than me. I'm not floating away by any means, nor am I dropping like a rock, and for all intensive purposes my surface buoyancy checks are fine so I am not sure where the problem lies. I have been diving a 7mm wetsuit with gloves, boots, and a hood. I have an 80 steel tank and 32lbs on my belt (I am kind of a big, floaty girl) to depths around 45ft at this particular site.

It feels like the obvious answer would be to shed a couple lbs off my belt, but as I said, my buoyancy checks on the surface are fine and my descent is not effortless. I am wondering if the problem does lie with the weight I am carrying or if I am just not using my lungs well enough to control my position in the water? OR is it completely acceptable to add a couple pinches of air to my BCD once at depth? I feel the latter is wrong, so I guess I am just looking for guidance.

And here I was, thrilled that I am not burning air so rapidly as I did in the first couple of dives. One step forward, two steps back. Ah, the joys of inexperience.

 

[kaerius]

Lung control is key. However proper weighting means you'll be neutral with an empty BCD at the end of the dive, when the tank weighs less due to consumed gas, so at the start of the dive, you'll be a bit heavy, it's certainly a good idea to compensate for this by putting some air in the BCD, just remember to gradually vent it as the dive progresses. It's a buoyancy control device, learn to use it, but do also remember that your lungs play a large part in buoyancy control, deep breath and you go up, exhale and you go down, I'm sure that was part of your course training. Basically you use the BCD to get neutral, and then control your position in the water with your lungs.

As for descending, you can go head first and kick, certainly beats flailing your arms around(which will make you go through air quicker). In fact, try to get in the habit of tucking your arms in and not using them during the dive, except where you need to(equalizing, manipulating gear, signaling and such).

 

[Bossman]

I've been diving for about a year and still sometimes struggle with the same scenario you describe, especially when adding a new/different piece of gear. Buoyancy checks on the surface will get you close, but you need to dive your configuration and adjust your weight based on the results you see. It sounds like the only reason you have the extra weight is to get down at the beginning of the dive, and you're concerned that if you take anymore weight off you'll have a more difficult time getting down. Practice your technique for that initial descent. Feet first is usually best, but you have to ensure that you drain your BC completely by leaning to the side and holding the vent on the inflator high. Next, take a big breath and then exhale forcefully as you drop yourself in the water. It's usually getting down that first 3-5 feet that is the most difficult, and if you get your technique dialed in it's much easier.

You can try to take off 2 lbs. at a time and see how it goes. Alternatively, you can buy some 8 oz. fishing weights and use them to help take off 1 lb. at a time (take off a 2 lb. weight and add the two 8 oz. sinkers).

I spent a week last fall diving the Bay Islands and the instructors told me I'd make a good tec diver because my trim was incredible. A few weeks ago I dove in the Atlantic in a 7mm farmer john with 30 lbs, and fought the weight the whole time after experiencing the same fight as you to descend. We all need lots of practice with different configurations to get it right. Make sure you keep notes in your log book for the gear config, wetsuit thickness, etc and how much weight you use with the config. Also make sure you note fresh or salt water, so in the future you can look back and adjust accordingly.

 

[Hypno-toad]

Basically you use the BCD to get neutral, and then control your position in the water with your lungs.

While we learned this in our training, it does take just using it to really get it. I am starting to get it. While swimming, say there is a tall rock on front of me. I take a big breath, up and over, exhale to get back down. Same with navigating through lobster trap/buoy lines. But here is where my newness shows. At this particular site, you have to kick out pretty far to get beyond 20ft depths, and once get do get to the 40ft range, I can feel my buoyancy change. Would I be wrong to add a puff or two to my BCD to compensate or should I really just be trying to stay up with my lungs? I have watched the other divers I am with very, very closely to pick up on their techniques, and I have not noticed them adding air to the BCD. They may be doing it quick or when I am not looking, but it seems as if they are not. Right now, I am an airhog (but getting better) and I think working harder to stay off the bottom is not helping me with that. I DO like to streamline myself (except when wrestling lobsters) but it's hard when a hand is constantly having to reach out to make sure I don't drop myself onto the rocks and my whole body is fighting with "up".

Bossman, I think you are right. I have been diving the same configuration in my dives, but it might take some playing around. I live right on the coast of Northern Massachusetts so I will almost always have at least 5-7mm wetsuits with gloves and hoods in salt water. I don't see my config changing much except for, as you said, new gear or a location change.

 

[kaerius]

At this particular site, you have to kick out pretty far to get beyond 20ft depths, and once get do get to the 40ft range, I can feel my buoyancy change. Would I be wrong to add a puff or two to my BCD to compensate or should I really just be trying to stay up with my lungs?

You would be correct. And yes, do add another puff or two. The reason your buoyancy changes with depth is that gas compresses under pressure. So any air in your BCD also compresses, making you less buoyant, since it now displaces less water*. The opposite is true while ascending, the air expands, which is why you need to vent air from the BCD on your way up to control your ascent.

The same happens with a wetsuit, it gets less buoyant and provides less insulation the deeper you go because the tiny air bubbles in the neoprene compress at depth.

*I won't get into archimedes principle, but you can look it up.

 

[thimp]

Being a new diver I also am working on the buoyancy and weight dilemma. I think the compression of the neoprene wetsuit (and boots) under the pressure of the water at greater depths plays an important part. In the first 12 feet the buoyancy is positive (resulting in a force up) below that it is much less to even neutral.
In the long run we should be able to lose some weight because we learn to overcome the shallow water issues, and be better trimmed below. The less air in your BCD the better, I think, beacause of stabiity and less waste of prescious air

 

[TSandM]

Well, we first need to make a clear distinction between correct weighting and your state of buoyancy at any given time.

Correct weighting means that you are carrying enough weight to be able to make stops at the end of the dive, with a near empty tank. Precisely how many psi left, or at what depth you should be neutral, we can argue about -- but I think everyone would agree that the goal is to remain in control of your position in the water column at the end of the dive.

If you are properly weighted, you will begin your dive so that, with an empty BC (and suit, if you are using a dry suit) you will be negative. This means you will have to add air to your BC to be neutral in the water -- this is the "compensation" part of "buoyancy compensator", because you are compensating for the mass of air you are going to exhaust into the water during your dive.

If you don't put enough air in your BC to compensate for this amount of air, you will be negative. This means that, when you stop swimming, you sink. It doesn't mean you are overweighted -- it just means you haven't fully compensated.

So why do you do this? (It's common, BTW.) There are two very plausible reasons. One is that you don't feel very secure or controlled when you are neutral, because in that state, it is so easy to make a mistake and get light and begin to ascend without intending to. Many new divers dive negative and swim up, because they feel safer sinking a little than floating too much.

The second factor is probably even more common, and takes a moment to think about. If you carry all your weight on a weight belt, or in weight pockets at the bottom of your BC, you may be properly weighted but out of balance. You can think of your body as a plank sitting on a fulcrum which is your center of gravity underwater. If you add weight to the bottom half of you, you'll tend to tilt feet-down, since the "lift" (the air bladder of your BC) is at the top half of you.

If you are feet down and you kick, you push yourself upward in the water. If you are neutral, you will ascend. If you are negative, you will counter the drive upward with a tendency to sink, and you will remain at the same depth. But you are wasting a significant part of the energy you are expending to kick, to achieve no net displacement at all! This is one of the reasons new divers go through air so fast.

So one test you can do is to get in the water with a buddy. Try to get yourself into a good horizontal position, with your arms folded underneath you or out in front, and your legs straight out behind you. Once your buddy says you're in good position, stop finning and see what happens. If you tilt feet down, you know you need to move some weight up onto your back or shoulders to balance correctly. If you don't, then you are probably just diving somewhat negative to feel safe, and more practice will likely fix this.

 

[Meggie66]

I now have around 40 dives and have continually struggled with the same issue you describe, especially the balance between an easy descent and staying off the bottom. I finally got it sorted at around 20 dives. What has helped me is:

On descent:

- exhaling when I vent my BCD (while of course being careful not to commit the mortal sin of holding my breath);
- making sure I'm not unconsciously finning while trying to descend;
- not being too worried about what position I descend in - I tend to naturally go feet up (having floaty ankles), and trying to correct this at the surface just results in my staying at the surface - now I get a few metres down and then correct my position;
- using the shoulder dump as well as the hose on my BCD, to make sure I'm getting all the air out. If you don't have a shoulder dump, turn slightly so your hose is higher, and continually vent it - not all the air comes out instantly;
- on a shore dive, surface swim until the water is around 5 metres/15 feet deep, rather than trying to descend at a shallower depth.

At the bottom:
- add a milisecond's puff of air to your BCD, and wait 10 seconds or so to see if you need more - remember it can take a few seconds for the additional buoyancy to make itself apparent.

Using a combination of the above, I've got my weight from 30lbs to 21lbs, without struggling to do safety stops at the end of the dive.

While you're working all of this out, it's probably best to do slightly shallower dives, to make sure you can do a safety stop.

Hope some of this helps, good luck!

 

[on_two_wheels]

One other note....as everyone is saying you need to exhale and deflate your BCD fully. However, timing both of these can make a big difference. What I found helped me a LOT was to start deflating my BCD before exhaling. If you're weighted properly you're going to at least sink enough for your face to submerge. It's at this point that I exhale VERY deeply. This does two things: 1) Forces even more CO2 out of my lungs. 2) Lets me drop another few feet to the point the increase pressure around me will aid in the rest of the descent. While I may not drop as fast as some others, I'm certainly not pushing around a lot of weight during the dive AND can hover on my safety stop (or any other time).

Once nearing the bottom, I'll flare out and add one large puff to the BCD. I'd rather have to dump a little air than end up hitting the bottom and silting or hitting reef. Then I just fine tune it to the point I can ascend/descend with breath control.

Some methods work well for some but not others. I've watched/listened to how many others do it until I found one that worked well for me. I suggest you do the same. For what it's worth, I did my first 15-20 descents head first because I couldn't get myself down feet first. Good luck!!

 

[rk288]

Seems like all new divers have similar stories. Mine are no different. I finally got away from swimming down by exhaling strongly and using both dump valves on my BC all at the same time. I'm weighted now so that I never add air to my BC and control every thing by breathing.
I was very surprised to finish a night dive neutral in 3 ft of water with 110 lbs in my Al80 tank...seems like the more you do it the better you get...