Buoyancy Tips...

[Teamcasa]

I dont like the "no" air in BC at 15ft with 500psi in the tank.

If for some reason (you run low or air share with buddy) you'll arrive at the stop depth with less, be too light and unable to hold the stop.

Should have a little bit of air in the BC at that depth to cater for this.

Why? When I make a stop at 15'-20' and have 500-700psi left, I want to insure I don't pop up for the last 10' when I'm done hovering. I can always add a quick shot of gas if I need it.

I normaly dive with a full 7mm suit in SoCal - steel tank HP100.

Dave

 

[String]

Totally empty BC with 500psi and neutral means less than 500psi you'll be positively buoyant which is never a good situation.

You need to be slightly negative with an empty BC with that much gas just in case.

 

[Charlie99]

......... duplicate post ...................

 

[Charlie99]

Why? When I make a stop at 15'-20' and have 500-700psi left, I want to insure I don't pop up for the last 10' when I'm done hovering. I can always add a quick shot of gas if I need it.

I normaly dive with a full 7mm suit in SoCal - steel tank HP100.

Dave

If you don't have any air in your BCD at 20', 7mm suit, and 700psi in your tank, than you either need to be breathing towards to the top of your lung capacity, or you need to have a bit of air in your BCD. Otherwise you'll be too light for a controlled ascent to the surface, or with an even emptier tank.

Can you hold a 15' stop when you have just 200psi left? Can you hold a stop, i.e. control your ascent at 10', 8', and 5'??? If you are right at the edge with your wetsuit compressed by 15-20' of depth and the extra pound or so of 500-700psi, then you won't be in control with a pound less gas and a few pounds more buoyancy in the wetsuit.

IMO it's OK to have to breathe shallow down near empty lungs to keep a stop at 5', but you really do need to be able to stop there.

The differences in weighting we are talking about are typically within the 5+ pounds of difference in buoyancy between full lungs and empty lungs, so you have to take that into account, as well as the amount of gas in the tank and the depth of the stop when you describe weighting.

 

[tampausmc]

how does all of this work when you are diving a set of double steel 108s or something? I just bought my tanks and was planning on getting a doubles setup....i think i'm going to be way over weight no matter what. So i'm assuming that my breath won't have much of an effect on my buoyancy since i'll be far overweighted i think. Any info on this? Thanks

one other thing...when diving with a single 108 and hit a current it tends to want to roll...how can i stop this? do i need to put more weight in the front? but if so then i would be considerably overweight...my last dive i had 4 pounds in the front with the steel tank and that seemed overweight....

 

[timle]

No matter how much you weigh if you get neutral (using your BC) with normally inflated lungs then a deep inhale will make you positive. However the more mass the longer it will take to overcome your inertia and see the effect on your buoyancy.

 

[String]

With a twinset you carry less lead as the weight of the extra tanks, backplate and so on does the same job.
However there is more of a swing from full to empty tanks (especially if adding stages). You may end up starting a dive 17lb or so heavy to end a dive neutral with all the gas gone. The physics and concept doesnt change though.

If you're neutral and a full breath makes you 6lb positive then that'll be true for anything from a single tank to twins with stages.

Buoyancy i find easier on a twinset due to the increased intertia, its harder to change depth or to put it another way, very stable to keep a depth.

 

[PerroneFord]

Buoyancy i find easier on a twinset due to the increased intertia, its harder to change depth or to put it another way, very stable to keep a depth.

By the same token, when you LOSE it, it's MUCH harder to stop the runaway train!

 

[TekDiveGirl]

Kimber, you don't know me and I don't want to hijack this thread but it's so nice to see you back

Thanks!

 

[TSandM]

Joe Talavera gave me a real good concept for breath/BC buoyancy control. He said, "There's only a small window -- maybe plus or minus two feet or so -- where your breath can stop what's happening. Get beyond that, and you should go directly to venting/adding air, because you simply don't have the volume to do the job with your lungs." For me, that window is VERY small, so I have to stay extremely alert to variations in my depth in order to avoid having to correct with my wing. Luckily, with doubles, the deviation starts slowly enough that I can usually detect it within that window, unless I'm distracted by bag shooting or air sharing or something of the sort.