Question BCD failure

[boulderjohn]

Let's start with the most common method of determining your weighting. You are supposed to take a normal (not deep) breath and dump ALL the air from your BCD. You should then be floating at eye level without doing any kicking.

If you are properly weighted, you should have no trouble staying on the surface with an empty BCD. Unfortunately, most new divers are overweighted, some by a whole lot.

In almost all cases, you will be carrying ditchable weight. If you have a BCD failure and cannot stay on the surface, you drop the weight.

 

[boulderjohn]

Or a full tank is also positively bouyant?

I wanted to make this point separately from the point above about proper weighting.

Your buoyancy depends upon the weight and volume of you and all your gear together, not just one part of you and your gear. Some of that total package wants to float. Some of it wants to sink. In most cases, your total package wants to float, and that is why you carry weights. You take an appropriate amount of weight so that you can sink, otherwise you are a snorkeler and not a diver.

Different scuba tanks have different amounts of buoyancy. The most common tanks are made of aluminum, and at the beginning of the dive, they are a few pounds negatively buoyant. At the end of the dive, they will be a few pounds positively buoyant. The difference is the amount of air you use during the dive. A steel tank of the same size as an aluminum tank is heavier and thus less buoyant. That means that if you use a steel tank and everything else is equal, you will not need to carry as much weight. During the dive, that steel tank will become more buoyant by the loss of air as well.

Summary: Your buoyancy is based upon your entire package, including the weights you carry. If you use an aluminum tank, you will need more weight than you will with a steel tank. During the dive, you will become more buoyant because of the loss of air in the tank, and it does not matter whether it is an aluminum tank or a steel tank--you become more buoyant by the weight of the air you lose.

 

[CT-Rich]

Always plan your configuration as if you were going to have to swim home. Boats can lose you, currents can carry you, you can miss read a compass bearing. Ditchable lead is your redundant buoyancy and is bullet proof reliable.

 

[SouthernSharktoothDiver]

Others have already posted good advice on weight configuration, I just wanted to add an extra point: redundant buoyancy is a thing some divers practice. An SMB can be used for this purpose, but it's something of a "pliers for a wrench approach." Divers Ready, IIRC, has a good video discussing other options, but basically, a lift bag works well if the bottom depth is above the deepest you can dive (ie, if you sank, you wouldn't sink to dangerous depths and could deploy the lift bag as your leisure.) Alternatively, you could use a (rather expensive) dual wing BCD, which essentially has two, full redundant wings each attached to a separate hose. Finally, the simplest and lowest budget option (other than proper weight management, of course): Stay close to your buddy. Unless they're dangerously overweighted, they should have enough lift to pull you up with them.

 

[lexvil]

I can swim and float well... but not sure if laden with gears...

So, without all of the side tracking of you should do this or do that which are things you should think about, the answer to you question is ditch anything and everything that is fighting against you staying afloat! An SMB can be helpful so have one with you but ditch anything you need to without regard to what you have or will have to pay for it.

 

[Eric Sedletzky]

So, without all of the side tracking of you should do this or do that which are things you should think about, the answer to you question is ditch anything and everything that is fighting against you staying afloat! An SMB can be helpful so have one with you but ditch anything you need to without regard to what you have or will have to pay for it.

…and weight systems make the most sense to ditch. That’s what they have taught throughout the history of skin and scuba diving.
I’m going to pre-empt something that ‘may’ come up in this conversation, and just mention something I have seen posted before advocated by the proponents of having all non ditchable weight.
And that is to dump your entire rig if necessary, which to me is the most asinine thing I have ever heard.

 

[lexvil]

…and weight systems make the most sense to ditch. That’s what they have taught throughout the history of skin and scuba diving.
I’m going to pre-empt something that ‘may’ come up in this conversation, and just mention something I have seen posted before advocated by the proponents of having all non ditchable weight.
And that is to dump your entire rig if necessary, which to me is the most asinine thing I have ever heard.

Non ditchable weight is not a good idea even for a balanced rig but if that’s your thing ditch it all.

 

[CT-Rich]

I'll mention this because it has yet to be explicitly stated. Ditching lead is something you do to stay at the surface. You should be able to swim your rig up. Once there, you can make a decision on whether you can stay there. If the conditions have gotten much worse, or you realize you are struggling while waiting for a boat or have a long swim. Think about ditching your weights. It seems a portion of the diver deaths that occur in our area, are from cardiac events and not drownings. Out of shape, inexperience and heavy gear can be exhausting on the surface. Surface swimming is much more physically taxing (and slower) than swimming on scuba. If you have BCD failure, once you are up, stay on your regulator and see if you can hand your lead off to your buddy. Struggling will lead to panic and exhaustion.

 

[rx7diver]

Breathing from a snorkel allows you to get more of your (heavy) head down into the water while you're either waiting at the surface or swimming prone on the surface.

rx7diver

 

[halocline]

Thanks! One more question.. If I am at the beginning of the dive with a full tank, is it possible to keep afloat with the extra weight with deflated bcd? Or a full tank is also positively bouyant?

I have to say I’m a little confused about why this wasn’t very thoroughly covered in your OW class. Usually in OW class students spend a lot of time at the surface in scuba gear. PADI makes a pretty big deal of managing your buoyancy at the surface, because it’s apparently more common for new divers and OW students to have problems staying in control at the surface than underwater.

Anyhow, the answer to your question is that if you cannot stay at the surface with a full tank and deflated BC, it’s probably because you are overweighted. I see you’re from Malaysia, so I’m guessing you’re learning in warm water. Most divers wear a wetsuit tht provides some positive buoyancy, usually enough so that they must wear weight either on a weight belt or in pockets. In that case, you simply drop your weights at the surface if you’re struggling to stay afloat. This really, really should have been covered fully in your OW class.

If you’re not wearing a wetsuit and any additional weights, it does get a little more complicated because at the beginning of a dive, the scuba tank is negatively buoyant. A scenario that is not too uncommon would be a new diver, either overweighted or not wearing a wetsuit, jumps into the water with their tank valve still turned off and finds that they can’t inflate their BC. IME that will usually only happen once in a diver’s career; after an experience like that you learn to make sure your valve is open!

You also typically put some air in the BC immediately before entering the water; sorry to sound like a broken record, but this also should have been fully covered in your class. Since you’ve checked the operation of your BC seconds before entering the water, the chances of an immediate and complete failure are almost nil.

You’re asking good questions, in fact surface problems are really common with new divers, but if your instructor did not fully address these, then I would really want to know why. There are pretty strict standards set out by all the major certification agencies.