buoyancy test..... HUH ?

[Yazrick]

I have read a few posts that mention buoyancy tests, and to be honnest - this is the first I hear of it.

During my training the instuctor explained to us what it was, and in our qualifying dives we did a test (which I always thought I failed) since I never floated like a weightless feather.

My first dive after qualifying was in the predetor tank at the 2Oceans aquarium in Cape Town. The dive master there did not really pay attention to me until he noticed I was walking on the bottom of the tank on my hands.

He signaled to me to inflate my BC, but that just lifted me (almost out of the water).
We serviced and he tried to explain to me to use my breathing to get my buoyancy right, but not very successfully.

When I went out to sea, I got my bouyancy right (don;t know how), and for the first time I realised wht it meant, and the joy in diving when you are truely weightless.

Subsequent dives were not as successfull as I kept sinking to the bottom like a rock. Inflatting my BC to much made it difficult to stay in one place, and when I deflate my BC i sink like a rock.

It bothers me that I can not float and I often exhaust myself underwater trying to breath more or fill my lounges not my BC, or trying to get up or down to the desired level...

Is there any advice on how to get my bouyancy right ?

 

[jbd]

Sounds to me like you are overweighted. Your textbook from your OW class should have a section on how to do a weighting check. Follow that procedure and you should come pretty close. It would help if an instructor would work with you on this in a pool or other confined water.

If that fails or is not possible I sell a booklet that deals with learning and mastering bouyancy control. Its a small booklet but if you follow the procedures and do the practice scenarios you will greatly improve your bouyancy. The booklet details the methods I used in my OW classes.

 

[ScubaStarwatcher]

Hi Yazrick,

I'm just learning too, but there seems to be two distinct issues: Getting your weights right, for which a bouyancy test is useful, and learning to control your bouyancy underwater.

Getting your weights right is a case of kitting up, estimating the amount of weight that you need and getting in the water. Deflate your BCD completely and see where you float in the water. If your weight is right you should float at eye level to the water. Play with weights until you float at this height with a reasonably good breath inside you. Exhaling should make you descend. If you have a full tank of air when doing this test, add a further 5kg of weight to make up for the fact that your tank will be lighter after the dive.

On the surface you can partially inflate your BCD to let you float nicely and save energy swimming.

Getting your bouyancy control underwater takes practice. You shouldn't be thinking of inflating or deflating completely, but simply adjust by a little amount and wait a few seconds to see what happens. It can take a little while before any movement up/down becomes apparent. Breath normally while you do this.

Once you're neutrally bouyant you can "fine control" your up/down by being mindful of how you breathe. A good lungful will tend to raise you, but less air in your lungs and you'll descend a little. Obviously you're not holding your breath, just changing how you breath a little.

Bare in mind that as you ascend or descend, the pressure will make your bouyancy change again so you'll need to adjust your BCD slightly again.

It helps to play in a pool with a reference point such as a pair of steps or a mark on the pool wall. Practice "hovering" with the mark at eye-level. It can be tricky, but teaches you a lot when you get it right.

The last tip is to continue practicing. It gets easier as you get more experience mate!

Best Regards,

Mark

(As a newbie to diving, I hope any experienced divers will correct any mistakes I've made in here

 

[TwoBitTxn]

First, take a tank with about 500psi of air in it and fully geared, you should float at eye level holding a normal breath. You can do this with a full tank, you just need to add 2-4 lbs (1-2kg) of weight to offset the buoyancy swing of the tank.

Do this with each gear configuration for both salt and fresh water.

Next, remember, small bursts of air into your BC and wait for the change. It takes a few seconds.

Try to relax under water, and breath as normally as you can. Yes, its hard to breath normally and think about breathing.

If you can't get horizontal, try to find a way to move your weight up. Trim pockets, tank weights, so on.

I'll leave it up to others to rip on your instructor.

You are over weighted and you need to find your proper weight first.

Dive... alot. It helps.

TwoBit

 

[Plungebob]

Most divers I talk with brag about how little weight they dive with. I once dove with a buddy in the Bahamas who boasted diving with only three or four pounds, however he was clutching 15 or 20 lbs of camera equipment.
Im no expert but I know that over weighting can cost you your life. Here.s what you do .Enter the water with ALL your gear hang on to something like an ancor line . Now deflate your B.C.D. With your reg. in your mouth hold a normal breath. At this point you should float at eye level.Adding or subtracting weight untill you do. To be sure, exhale and you should begin to sink. Thats neutral. Now add about five lbs. You should now be a feather.
Keep a record of what your diving with ie. rubber, lead,toys etc. so next time ittle be a no brainer.

 

[Yazrick]

You guys ROCK !!!

I never knew that I was supposed to float at eye level with a full kit on

I'm all excited to get back into the water now, since I now have a way to get my buoyancy sorted

 

[Don Wray]

While holding a normal breath you should float at about eye level...you should begin to sink when you exhale

 

[herman]

You should float eye level with a normal breath AND ALL the air out of your BC. When you exhale you should start to slowly sink, no drop like a rock. Buoyancy control is a slow and deliberate process. Proper weighting is important but your understanding of the physics of buoyancy are much more important than being dead on with your weights. If you understand buoyancy you can dive with any BC or amount of weight, with in reason of course.
There are 2 basic problems I would suggest you consider.
Many divers tend to unconsciously fin when they are trying to descend feet first, they are finning up while trying to descend. To compensate for the finning divers will add more weight and dump the air in his BC, once the effects of the finning is overcome the diver starts to drop like a rock. To stop the decent a lot of air is added to the BC, in almost every case way too much air. About this time is when problem 2 comes into play. The simple fix is to stop finning and be properly weighted.
Problem 2 is more difficult to deal with. One of the most difficult concepts of buoyancy to learn is it's delayed response to changes. This is most likely one of the major problems you are experiencing. We are all use to things happening almost instantly, you press on the car's brakes and it immediately starts to slow down. This is not the case with buoyancy. When you add or remove air form your BC or take/let out a deep breath, it takes several seconds for the full effect of what you have done to take effect. New divers are way to impatient, they add air, nothing happens immediately so more air is added and maybe even a 3rd time. To make matters worse, each addition is bigger than before because "nothing is happening". Then the effects start to take hold and the diver starts to ascend. The accent starts to speed up, so the diver dumps some air, nothing happens, more air is dumped. About this time the delayed effects of dumping air starts to kick in and the diver is heading to the bottom fast. The result is yo-yoing up and down and having to constantly add and dump air. The solution is to be properly weighted and when you make a buoyancy adjustment, SLOW DOWN AND WAIT A FEW SECONDS to allow time for the effects of your change to take place. The art of buoyancy control is to know how much air to add/dump and when to do it to get the result you want.

 

[donnad]

i agree -being overweighted makes buoyancy control difficult. but i'm a fan now of making sure i have enough weight.......not trying to see how little weight i can dive with. who cares what the number is if it's right? i've experienced being underweighted by probably 2-3 lbs. and absolutely could not perform my safety stop because of it. added some lead the next dive and it was perfect, so there's a point of not being overweighted but having enough to be able to still do safety stop properly when tank is light ya know?

 

[spectrum]

The defining moment of correct weight is being able to do your safety stop with a nearly depleted (500 PSI) cylinder. At this point you should need little or no air in your BCD. You want to be able to make a controlled ascent all the way to the top or have the freedom to end a shore dive playing in the shallows. At this point we are talking about very few pounds difference. How much neoprene you have will make a big difference here.

Earlier in the dive due to the weight of your compressed air reserves and the compression of your neoprene at depth you will be more negatively buoyant and that's where your Buoyancy Compensator comes into play. Clever name huh?

The bobbing at eye level at the end of the dive with 500 PSI and an average breath is a good way to get darned close.

It's a very personal number dependent on your cylinder, neoprene, other gear and body mass.

Getting the weight number right will let you manage your position in the water column. Positioning it to get good trim will let you dive. When it comes together for you it is absolute magic. My wife and I each have a defining eureka dive.

During a dive you want to have a regular breathing patern so you don't want to be running a modified lung volume for a long period. However lets say you have wandered up a ledge and you begin to feel your body getting light in the water. Making a long exhale as you swim down will get you there without venting air from your BC. Taking a large inhale and exhaling very slowly will cause you to rise over an underwater structure, again without touching your inflator. Keeping an open airway is critical in all of these actions and the safe way to insure this is to keep breathing albeit slowly.

Pete