Buoyancy control techniques for a beginner

[butsee]

Hi All,

I am so glad that I can find this informative scuba diving website! I have just completed the Open Water course recently and I really fall in love with diving. Meanwhile, I am taking the Advanced course right now. however, I found that it's really difficult to control my buoyancy.

I was told to add more weight as I always ascent uncontrolly. My body weight is 48kg/105 lbs, but I use 12 to 13 lbs weight belt. Is it too heavy for me? Is there any ways to check the weight which is suitable for me? I heard that the water surface should be at my eye line with a normal breathe held, it is right?

I also heard that diver should inflate a BCD while desenting, is it truth?

I really want to learn more about scuba diving, especially the techniques. Any good websites suggest?

Butsee, an Open Water Diver

 

[Warhammer]

If your having alot of trouble with bouyancy and are currently taking the Advanced course, my advice would be for you to call your instructor to side and request he spend some extra time with you, one on one, on this. He should be glad to help, but it would be nice if you made it worth his while. Truth is you can talk about bouyancy till your blue in face and if you don't practice it you'll never get any better. Practice, practice, practice. Best way to practice is to make dives for no other reason than to do just that. If you have a good place locally, like a shallow fresh water quarry, to practice that would be ideal.

About your weight belt. It really depends on your equipment as to what weight you'd need. Wetsuits, drysuits and other equipment effect bouyancy greatly, so you have to add weight for them. My wife is about your size and with a 3mm shorty she wears 8lbs in salt water using an AL80 tank. If your diving a 3mm or nothing then I'd say you may be a little over weight. But if your wearing a 7mm then probably not. To check for neutral bouyancy, do this: With your tank empty(empty meaning at your ending pressure, say 300 to 500PSI on an AL80), you should float at eye level with your lungs full and your BC empty. When you release the air from your lungs, you should slowly begin to sink.

Yes, you should add a little air to your BC as you descend or near the bottom to avoid contacting the bottom because if your properly weighted you'll be a tad positive at the beginning of the dive. But just a little to keep from from hitting the bottom, to much will send you back to the surface. Try to fine tune your bouyancy with breathing.

 

[Mario S Caner]

Welcome to diving and the site, pass the word on about how great it is here.

In order to answer your buoyancy question, we really need to know the type of exposure protection, the type and size of the cylinder and the type of water you are diving in. The rest is fairly simple, at least as a starting point.

For example we can say that for the average diver, 10% of your body weight plus 4-6lbs when diving with a 7mm neoprene wetsuit and an Aluminum cylinder. Now having said that, it's important to note that every persons body composition is slightly different. Fat, muscle and bone have different densities and therefore have different buoyancy characteristics.

Like warhammer was saying, the best way to check for proper weighting is to deflate your B.C. entirely so that you float at eye level with a full breath and a nearly empty cylinder. Once you exhale, you will begin to sink. Boom, you're properly weighted. This is done with a nearly empty cyinder because that is what is going to more closely resemble the buoyancy properties of your cylinder towards the end of your dive. This will enable you to make a nice, comfortable safety stop at the end of your dive, without floating uncontrolably to the surface.

Since you now know how to get properly weighted, you will of course deflate your BC to descend below the surface, but then add air during descent. The reason's are quite simple. The increase in surrounding water pressure squeezes the neoprene, and therefore flattens it. When this occurs, you will become less buoyant and sink... faster and faster. To counteract the increasingly rapid descent, you will add air to your BC. Buoyancy control doesn't just happen on the surface. This will keep you at a safe depth, as well as protect delicate aquatic life.

You will also find that with experience, and a higher level of comfort, your weight requirements will change over time. Exp: I weigh 200lbs. With a fairly new 7mm full wetsuit, thick gloves and booties and a LP95 steel cylinder I use 6 lbs of weight.

Mario

 

[Beachman]

If you adjust your weighting on the surface as suggested above, there is no reason you should ascend uncontrollably so long as you are venting your BC enough on the way up.

Regarding descents, remember that your suit will compress from the increasing pressure of the water as you go deeper and deeper. A neoprene wetsuit will compress to its maximum at about 35'. When this happens, you will be "heavier" in the water and will sink faster. That is why you need to add small amounts of air to your BC as you descend to adjust buoyancy.

When you ascend, I suggest you vent enough air initially so you will be negatively buoyant and actually "swim up" for a while until you get the feel for how much air to vent little by little as you rise. Once you've ascended a few times keeping yourself negatively buoyant and swimming to the surface, you'll be able to adjust more closely and the swimming part will disappear.

Worst case for an uncontrolled descent is a crash landing on the bottom. Worst case for an uncontrolled ascent and missed safety stop is DCS....and that's serious. Be sure you have the ascents under control before diving over 60' or so!

As Warhammer says, it's all practice, practice, practice.

DSAO

 

[butsee]

Thanks for those who gave me those valuable advices.

In fact, I discussed the matter with my instructor and I was told to check my weight if I can float at eye level. I do agree that practice is to very very important, but in my case I could only make dives during the course where I am not able to practice the buoyancy control. Anyway, I would try to do make fun dives for just practising the buoyancy.

I am an Asian and is used to wear a 3mm neoprene wetsuit, 12 lbs weight and a AL80 tank in the salty water. I was tiold by my instructor that I could never inhale the BCD under controlled ascent. Therefore, I am used to fin up but I find it's very difficult to do the safety stop. Please kindly advise me.

Butsee, an Open Water Diver

 

[Beachman]

You should practice in a pool. Experiment with adding and removing small amounts of weight, inflating and deflating your BC with small amounts of air.

If you can find a combination that allows you to hang with little effort for several minutes at 6' in a pool, you should have no problem hanging between 15' - 20' for a 3 - 5 minute safety stop in open water.

Someday you'll wonder why this was ever a problem !

 

[glidingray]

I'm 48 kgs too. My exposure suit is 1.5 mm.

On certification I wore 4 kgs weight. It was difficult for me to descend. And once I glided the seabed, I was kinda too heavy for my own good that I almost crushed the reef. Then I would inflate the BCD, then I would inflate too much air to it that I would fly away. So much for those "eye level" tips from the instructor.

Last year I was fortunate enough to move to a city close to a spectacular dive site. 15-20 m visibility and no current. It is perfect for buoyancy control practice.

The key for me was familiar surroundings so I could be more relaxed and more observant to myself.

It was difficult for me to descend because I tent to inhale more air while descending instead of emptying my lungs. Due to nervousness...of course.

During the dive most of the time I almost crushed the reef because I wore too much weight. Then I would inflate too much air that made me fly away from the reef. After I corrected my descending technique and wore 1 kg or 2 kgs less (depends on my familiarity of the dive site), I have never had to inflate my BCD... not until the end of the dive on the surface.

Being completely relax also made me more observant to the way I breathe. You might not believe it now, but good buoyancy control is indeed based on the way the diver breathes. You need more bottom time to gain this skill. My certification was 4 years ago and I mastered the skill only earlier this year. Be patient and relax...there are other people worse than you

The percentage of body fat also makes difference. I used to be able to float on swimming pool water easily. After I squeezed this fat away, I dive easier. But of course... no more sleeping in the middle of swimming pool like before

Oh, and if you wear weight belt like I do, and not some sophisticated BCD which you can spread the lead weight all over it, put more leads on your stomach than on your back. More lead on the back has made me move in standing position, very tiring. By putting more on my stomach, I'm able to dive streamline efficiently.

Ray

 

[Mario S Caner]

Glindingray,
What's important to understand when adding air to a BC, is that it's not immediate. It takes a second or two for the addition to take effect. Small bursts of air is what you need, if you are floating up and down, you're being a little too impatient. I've had students show near perfect buoyancy abilities by the end of the first dive. I don't however have any students finish my course before they can demonstrate proper buoyancy behavior. There is always a multitude of different confined water exercises that have to be practiced and mastered in a pool. Some people take longer to catch on than others, but beleive me everyone catches on, because that student practices under the careful supervison and proper guidance of his/her instructor before he/she progresses to the next phase.

Now you all know...
Mario

 

[LanceLisenby]

I keep having this problem when going shallower. I try inflator hose, chest dump, and lower back dump! To dump inflator or chest pull string I have to go vertical head up. To dump low back pull string I have to go butt-up! Is this normal or is this a quirky bcd? Its a Sea Elite Hybrid.

 

[TSandM]

Lance, physics is inexorable. Air will always rise to the highest point in its container underwater, so you always have to get a dump to a place where it is where the air wants to go. It should not be necessary to go completely vertical to dump from your shoulder dump, though; if it is, the dump take off is too far forward on the shoulder of the BC. It should be sufficient, with normally constructed BCs, to roll a little bit to your right, and perhaps a little bit head-up.

It is very likely that the reason you feel you have to go very head-down to dump from your rear dump is that your normal posture isn't completely horizontal. If you are head-up, then getting a little head-down to move the gas to the rear dump is going to feel like a BIG change.