Not so fine points about bouyancy control

[tparrent]

For my first three or four dives after certification, I had typical newbie bouyancy control problems: always adjusting air in the BC, improper orientation, legs and arms flapping around, bouncing up and down in the water column.

Fortunately, I had some good buddies and a good divemaster on my first trip. I became fairly proficient at breath control to adjust bouyancy and I learned to stop all that flapping around. By my tneth dive I could ascend/descend ten feet or more with simple breath control in order to see something interesting. I never touched anything but could comfortably float an inch or two above the coral. The last few dives on my first trip, I was able to hang just fine on the safety stops without use of the ascent line. I also dropped six pounds of weights in my first 8 dives following certification. I was feeling pretty good about my control.

Last week I went on my second trip. I was very comfortable with everything and really enjoyed myself. Again, my bouyancy control was excellent when swimming or hovering at depth. I could easily glid along and make micro adjustments to float above coral heads or descend to see lobsters. Below 40 feet or so everything was dialed in just right. Even at 100 feet I only needed a tiny shot of air in my BC to neutralize. My arms stay locked into my chest and my feet are crossed and perfectly still unless I am intentionally finning.

Unfortunately, that first 40 feet of water still presents problems. Specifically, I needed to pull myself down the descent line on each dive. I fully understand why bouyancy is easier to control at depth but I have not figured out how to descend easily. I completely empty my BC AND my lungs but I still float near the surface. Those first 10-15 feet are the worst as I have to hand over hand down the line.

On the safety stops I had to hang on the line to stop ascending. I could feel myself getting light towards the end of the dive because I am still sucking more air than the more experienced divers (I'll end up maybe 100 psi lower than others in the water). There was some surface wave action that would stir up the water some but I resisted finning in reaction to it because I could see the DM just hanging out off to the side with no problems. I want to be like that!

Now the soultion to my "problem" may be as simple as adding more weight. I actually did add a couple of pounds on my second set of dives this week but it did not make much difference. I already carry a lot of weight (18 pounds in full 3mm, warm salt water and AL80) because I am ... er .... "naturally bouyant" due to a rigorous training regime involving lots of pizza over the past few years. Seriously, I am diligently losing my own weight now and I know that will help but that takes time.

If I add any more weight to my BC, I know that I will need to add some air once I get down to 30-40 feet. That means I will have to carefully and fully evacuate the air as well on my way up or the weight will not have accomplished anything.

Do those of you with very good control find yourselves adding air when you get to the bottom or do you dive the whole dive with a basically empty BC? I never saw the DM's on either of my trips ever touch their inflator hoses but that doesn't mean they didn't do it.

It is important to me to get the shallow bouyancy under control because I really want to do more shallow dives in the 10-40 foot range. So far, everyone I have been diving with always wants to go deep. That's fine and there's definitely some cool stuff down there but I would really like to spend more time in the far more colorful zones on shallow reefs. As wonderful as my dives have been so far, with crystal clear water and sunny days - they still don't compare to the snorkeling and resort dives I did 20 years ago in 15 feet of spectaculalry colorful conditions in the Bahamas. In order to enjoy the shallow dives now I really want my bouyancy zeroed in.

Thanks for any suggestions.

 

[The Kraken]

TP,
To get your weight right, you need to start at the end of your dive, not at the beginning.
You need to be able to be neutrally buoyant on your safety stop with ~ 500psi in your tank.
Whatever amount of weight is required for you to do this is the correct amount of weight.

the K

 

[TSandM]

In my admittedly limited experience, if you are having trouble getting down at the beginning, and trouble staying down at the end, you are probably light.

The last trip we took, I think I had my weighting and buoyancy control down pretty well. I was carrying 8 lbs with a 5 lb backplate, so 13 in all. Descent was effortless and I controlled my buoyancy at the end of the dive with no air in my BC from about 20 feet up, holding stops without problems (spent a large part of the latter section of one dive at 4fsw over a reef!) But yes, I did have some air in my BC at depth, especially at the beginning. After all, you need to start the dive negative by at least the amount of air in your tank (minus your desired reserve at the end), or you'll be positive at the end.

 

[MikeFerrara]

If you are wearing any compressable exposure protection at all you are going to have to add some air to the bc as you descend. There isn't any shame in that and that's why you're wearing it.

As the others have said, you need to be able to remain neutral at the end of the dive. You can do a buoyancy check with a near emty tank or do it with a full tank and add 5 or six pounds (the weight of the air in the tank). Ascents and descents are probably when it's most important to have good control of your buoyancy.

 

[spectrum]

If you are as relaxed and comfortable as you sound then you need more weight.

Correct weight is defined (in my words) as ebough to make your safety stop in open watewr and to then amke an orderly controlled surfacing with 500 PSI left in your cylinder.

If you need the the rope to hold you down at the stop you etiher had air trapped in your BC, not enough weight or were doing something with your fins that made you rise.

Like wise the extra 5 pounds of air you start the dive should make you drop with a good exhale once you are set for the end of dive condition.

Being "naturaly buoyant" and diving AL-80 cylinders (that are relatively buoyant) in salt water will require some weight. Remember that you need what you need and the difference between 16 and 24 pounds or whatever your right number should be a non issue if you are fit to dive.

The "bobbing plumb and still at eye level with 500 PSI in the cylinder" is probably the easiest basic byouyancy test. If you make the test at the start of the dive with a full tank add 5LB for air usage. Also re-check at the end since at the onset of the dive you may have had some stow away air in your gear that caused you to include unneeded weight.

Adding air to your BC is not a sin, that is what it is there for. Your wetsuit, even a 3mm will loose some buoyancy with compression and your tank mass (hence buoynacy ) will change over the course of the dive. Compensate for it. It's great that you have unlocked the secret of your lung volume but you can only do so much with your lungs over the full range of conditions.

Pete

 

[BigTuna]

Those first 10-15 feet are the worst as I have to hand over hand down the line.

On the safety stops I had to hang on the line to stop ascending. I could feel myself getting light towards the end of the dive

This description says to me that you need more ballast. Your problem isn't about control. BTW, for what it's worth, I use 16 pounds of lead with a 3-mil suit and an AL80. Also BTW, congrats on your good control!

It sounds like you might have gotten neutral with a full tank. If so, you'd be 5 or 6 pounds or so positively buoyant at the end of the dive, because that's the weight of the air you remove from the tank by breathing from it (assuming you get down to 500 psi or so, as Kraken suggests). So you could try adding those 5 or 6 pounds to your initial ballast to compensate for the weight the tank will lose. That should get you close enough so you can add or remove a little weight on each successive dive until you're dialed in. Sounds like you're already on this road. Just keep on it.

You're right--at the beginning of the dive you'll need a little air at depth to balance the extra weight. Even if you didn't change depth once your descent is complete, to stay neutral you'd need to slowly bleed air from your BCD as the dive progresses and your tank becomes more buoyant.

Another approach is to have some clip-on weights (1- and 2-pound increments) available at the safety stop, so you can add them until you can get neutral again. Ask the DM to either carry them or clip them onto the down line, or maybe hang them over the side of the boat.

You can use these approaches in a pool, too. But if you do that, you'll need to add about 3% more weight when you go back to salt water, because it's more buoyant than fresh water. The 3% is applied to your total weight: dress in full kit--tanks, ballast, and all--and stand on a scale.

because I am still sucking more air than the more experienced divers (I'll end up maybe 100 psi lower than others in the water).

That's not related to this problem. Using up your air faster only gets you (and your buddy!) to the safety stop sooner.

 

[pasley]

Adding a little air to the BC at depth is what it is there for. Being neutral at the end of the dive with 500 or less PSI in the tank is more important.

One thing you may want to check on your dive is......(wait for it).....are you unconciously moving your legs and finning up when you are trying to go down? I have noticed many (including myself) tend to do this. Kind of an automatic thing, we get in the water and the legs start moving back and forth without us thinking about it. Also if we tend to um, tread water with our hands and arms, all this to keep up up, while we want to go down. Just somthing to think about. Concentrate on keeping your feet and arms still and exhale,exhale,exhale,exhale,small sip of air,exhale,exhale unitl you are past 10 feet or so.

Now for the good news, new divers, who are normally overweight don't have these problems, as they drop like a rock. a properly weighted diver has to concentrate more on exhaling and will float gently and slowly down. Sounds like you are on the right track on buoanck, just a little tweaking to do. As you dive more, you will have to make small adjsutments from time to time due to aging on the wetsuit and the um, reduction in other measurements. Diving is fantastic exercise. Do it often. 30 minutes at 33 feet twiddling you thumbs counts as 30 minutes sweating on a stairmaster to your heart (its a pressue thing).

 

[TSandM]

Wanted to add that, if you're only ending up 100 psi below other divers, that's not at all bad, and may be more related to your size and fitness level than your diving technique.

 

[theskull]

In my admittedly limited experience, . . . .

Hey TSM,

You may FEEL limited in experience since you regularly dive with some pretty excellent buddies. But I KNOW from reading your contributions here that you have gained enough skill and experience to be quite a good diver and source of knowledge.

So don't sell yourself short. And don't take my word for it; ask your regular dive buddies if I'm not right about this. Big to you. You make this forum a better place.

theskull

 

[tparrent]

I thought I might be a little underweighted and that seems to be the consensus here.

I have become a real stickler about being aware of any extraneous body movement (because it looks so cool to be so still ) so I am pretty sure I am not finning and I know my arms are locked in. Going up or down or hovering, I tend to cross my legs to ensure they don't start doing things on their own.

On my first dive trip, my buddy was nuts about getting both my ballast and his down. He's got well over 100 dives. At that point I had my checkout dives and that was it it. It was a real point of honor for him for some reason. Anyway, we were diving steel 72s and then the DM switched me to steel 80s to give me extra air and more weight. That worked very well.

Does anyone know the weight difference between steel and aluminum 80s? I was good at 12 pounds with the steel and light at 16 and even 18 with the AL80s.

The good news is that as my body weight drops I should be able to shed some external ballast as well EXCEPT that there is a good chance I will soon move to Southern California and I don't think I'll be diving a 3 mm there!

If 30 minutes underwater burns the same calories as 30 minutes on a stairmaster, I'm going to go diving a whole lot more often! Maybe I'll put a 40 foot pool in my backyard