Why use a BC anyway?

[steve1122]

Two years ago, I attended a basic scuba class, and on my very first dive, I ruptured my eardrum, so I was never certified. I was overweighted on the dive, and my attempts to regulate my depth with the BC only made things worse. I found that a small amount of air introduced into the BC at depth expanded as I rose, causing me to rise faster and faster without adding any more air. I floated up and down as I added air, then let it out, with very little ability to control my depth. I ended up on the surface, then dumped the air out of the BC, causing me to sink like a stone. I sank so fast, I didn't have time to equalize, and my right eardrum let go.

Since then, I have debated whether I want to give this another try. I understand that my instructor let me down in a big way- this should never have happened. I think I might try again in the spring, obviously with a different instructor. But I am left wondering what good a BC does me when its buoyancy is so hard to control. If I am properly weighted, I shouldn't be sinking or rising at any great rate anyway. If I get into trouble, I can drop the weights and rise with the buoyancy of the wetsuit. It seems that the BC adds a potentially dangerous variable that only complicates things for a new diver, and I would be better off without it. Any thoughts?

 

[kierentec]

if this was not explained thoroughly before you ever even got in the pool, you need to find a new instructor. he is the reason you got injured.

 

[kierentec]

the BC should really only be compensating for the additional weight of the gas in your full cylinder at the beginning of the dive, as well as any compression of your exposure suit. You use your lungs to make minor adjustments throughout the dive. at the end of the dive, you should have almost no gas in your BC at your safety stop.
it is also very convenient to be able to inflate your BC at the surface while waiting for your turn to exit the water, lead is WAY too expensive these days to be dropping it at the end of every dive

 

[dumpsterDiver]

Two years ago, I attended a basic scuba class, and on my very first dive, I ruptured my eardrum, so I was never certified. I was overweighted on the dive, and my attempts to regulate my depth with the BC only made things worse. I found that a small amount of air introduced into the BC at depth expanded as I rose, causing me to rise faster and faster without adding any more air. I floated up and down as I added air, then let it out, with very little ability to control my depth. I ended up on the surface, then dumped the air out of the BC, causing me to sink like a stone. I sank so fast, I didn't have time to equalize, and my right eardrum let go.

Since then, I have debated whether I want to give this another try. I understand that my instructor let me down in a big way- this should never have happened. I think I might try again in the spring, obviously with a different instructor. But I am left wondering what good a BC does me when its buoyancy is so hard to control. If I am properly weighted, I shouldn't be sinking or rising at any great rate anyway. If I get into trouble, I can drop the weights and rise with the buoyancy of the wetsuit. It seems that the BC adds a potentially dangerous variable that only complicates things for a new diver, and I would be better off without it. Any thoughts?

Some people feel that way about scuba gear and think we should all freedive... T

The air in the BC and your bouyancy represents an unstable equilibrium. As you describe, if you are balanced at one depth and ascend a tiny amount, you will now be too light and will tend to continue to float to the surface. Similarly, if you are balanced and go down 6 inches, the air contracts and you will become heavy and will begin to sink, faster and faster. It sounds like you understand this, however it is a balancing game. just like a 5 yr old will learn to balance a bike and somehow learns to lean and pedal and move the handlebars side to side, all at the same time so that he will no longer crash, you too will also learn to balance an inherently unstable system..with a little practice.

Yes it can be dangerous, just like riding a bike, but the bike and the BC both have advanatges that out weigh their dangers in most situations

 

[g1138]

They used to do it the way you're suggesting, however the problem came with changing depth. You would have to weight yourself for your max depth. Any higher than that and you may be constantly kicking to stay down. Any lower and you'd be kicking to stay off the bottom. At your set max depth (the one you weighted yourself for) you'd be neutral.
That's the problem with air expansion and compression of your wetsuit.

With a thick wetsuit this becomes even more exacerbated. The solution to this was the BC. You can now weight yourself to be neutral at 15ft w/ 500psi in your tank. Any depth you go to, if your BC has the lift capacity, you can be neutral at any depth. That's the purpose of the BC.

It is hard to master but it isn't impossible for a new diver to become even slightly competent by the time they go for checkouts. I suspect you were overcompensating with the BC input, along with the overweighting this led to your problem. I also highly suspect your instructor did a poor job at instructing you.

Give it another shot with a different instructor.

 

[Bob DBF]

Although they are quite handy, when I started diving we didn't use them. I did have a may west for floatation on the surface, if necessary. Check out the vintage divers forum for the details; however, don' t expect to certify without a BC.



Bob
-----------------------
I may be old, but I'm not dead yet

 

[pasley]

Unfortunatly many instructors rush the class and you do not get the time to master buoyancy control. 2 afternoons in the pool is IMHO not enough to master this skill. My students sit in the lotus position and control their buoyncy 1/2 between surface and bottom of pool before we go to the ocean. You issue is basically one of not being taught not only the fundamentals of buoyany control, but given adequate time to practice in the pool.

Fundamentals of the decent
1. When the water is over your head on the decent, STOP dumping air out of the BCD
2. Add small amounts of air every 2-4 feet as you decend once you are past say 8-10 feet. You should float down slowly, in fact you may feel the need to check your depth guage to verify you are in fact decending if you do it right.
3. As you approach your desired stop depth or bottom increse the air you are adding.
4. You should be properly weighted and going so slow that a large inhale will stop your decent.

Fundamentals of Ascent
1. Be slightly negative before you start the ascent
2. The BCD Power Inflator is NOT AN ELEVATOR BUTTON. Do NOT add air to start the ascent.
3. Vent air often during the ascent. You must stay ahead of the curve. Vent small amount often. Air increases 25-33% between 9 feet and the surface. Doubles from 33 feet to surface, Tripples from 66 feet to the surface, Quadruples from 99 feet to the surface.So vent early and often.
4. At 15 feet with 500 PSI in the tank and an emptyBCD you should be neutral. If not adjust your weighting.

 

[eelnoraa]

I think you should just do the class again with a better instructor.

... I was overweighted on the dive, and my attempts to regulate my depth with the BC only
[\quote]

Both of these are wrong

I can see diving without BC is possible for certain situation, ie. relatively small tank, thin/no exposure suit. But you need to learn to weight yourelf perfectly and control buoyance using your breathing. A good instructor to guide you on both.

 

[windapp]

I'm calling troll on this one.

 

[TSandM]

I don't think this is a troll. I've seen too many students with similar issues.

To the OP -- It sounds as though you needed more work in the pool, until you really started to get the idea of controlling your buoyancy. And you may well have been overweighted and had difficulty with control on your OW dives, but one doesn't puncture an eardrum unless equalization doesn't happen, which suggests again to me that you were just short on bandwidth, which means you weren't comfortable enough to go to open water.

Give the class another try. Even those of us with no intrinsic aptitude at all (I am one) manage to master the BC well enough to avoid injury, even during OW class. It does take time to make buoyancy control a thing of nuance, but I am living proof that it is something you can achieve, given determination and good enough coaching.