Not needing air for buoyancy control ?

[thomson_adam]

Hello All
I am a relatively new diver and have recently just got back from Jamaica diving.

Whilst there i noticed the only time i used my BCD was prior to getting into the water and after our safety stop for the surface.

We did some dives down to 120ft for deep diving and i never once had to add air.

Is this a good or bad thing ?

 

[Jai Bar]

Under the assumption that the water in Jamaica is warm and you were using a thin wetsuit (or skin, rushgard etc.) then it is good, meaning that you were not taking too many lead weights just what you need.

 

[Eric Sedletzky]

That’s about as good as it gets.
Congratulations!

 

[rongoodman]

Since you started the dive 5+ pounds heavy due to the weight of your unused gas it sounds like you were too light to hold a shallow stop with a minimal amount of gas. That could pose a problem.

 

[Eric Sedletzky]

Since you started the dive 5+ pounds heavy due to the weight of your unused gas it sounds like you were too light to hold a shallow stop with a minimal amount of gas. That could pose a problem.

He said they did their safety stop after going to 120’. He never mentioned having trouble holding his stop.
It sounds like he was perfectly weighted to me. How would adding weight improve that? All that would do is increase dependency on his BC.

 

[MidOH]

Were you finning the whole time?​

 

[inquis]

I think it's rather astute that you're asking this question! IMO, I don't think it's ideal to not use the BCD during the dive.

When ideally weighted, you will be neutral at the safety stop with no air in the BC and perhaps 500 psi in the tank (assuming an AL80 tank). As such, then at the beginning of the dive you will be 5 lbs negatively buoyant due to the additional gas you haven't yet breathed.

While one can compensate for this 5 lb (~2.5 kg) deficit with lungs or kicking while in a heads-up orientation, neither is a great idea. The former tends to accumulate CO2 (leading to a headache). The latter may inadvertently stir up or break coral when near the bottom and definitely consumes air faster. If you have a wetsuit, compression will make the deficit even more than that 5 lbs, as will being over weighted or using larger tanks.

Again, one *can* compensate without using the BCD, but that's literally right in the name (Buoyancy Compensation Device)!

FWIW, it's VERY common to be oriented fairly heads-up as a new diver, and you'd naturally leave yourself a bit negative to compensate. (Otherwise you'd ascend!) If this is the case, then simply repositioning some of your lead onto the upper tank band can allow you to maintain your desired orientation (including horizontal) and depth without kicking. The bonus is an improved air consumption rate. Using the BCD will then allow you to breath in a normal range.

 

[thomson_adam]

Were you finning the whole time?​

at the safety top ? if so . sometimes but there was also times i had my legs crossed.

 

[Belzelbub]

Whilst there i noticed the only time i used my BCD was prior to getting into the water and after our safety stop for the surface.

What do you mean by using the BC after the safety stop? Or do you just mean at the surface. You shouldn't add air to ascend from the safety stop.

We did some dives down to 120ft for deep diving and i never once had to add air.

Is this a good or bad thing ?

Depends. You should have some swing of buoyancy to account for the weight of the gas you breathed. If so, you should have needed to add some air either on descent or when you got to your dive depth to slow descent or establish neutral. From that point, you should just need to vent some gas as your tank gets lighter. You may also have been able to compensate for this by the way you are breathing. Don't try to use your lungs to compensate too much, though.

As long as you were able to hold your safety stop depth with an empty or nearly empty BC, then it's a good thing.

 

[Bob DBF]

Depends. You should have some swing of buoyancy to account for the weight of the gas you breathed.

Which would mean dumping a little air, not adding it.

If so, you should have needed to add some air either on descent or when you got to your dive depth to slow descent or establish neutral.

If he started neutral on the surface, with no wetsuit, it can be done without issue.

This is how I dove when I first learned, because the BC was yet to used in recreational diving. With a 7mm farmer John for the cold water here, I'm really thankful for a BC, but enjoy "skin diving" more.