Buoyancy help

[Xanthro]

A lot of beginners treat the BCD like an elevator. That's wrong. Treat the buttons on the BCD like brakes on a car.
At the surface, fully inflated, is like being parked on a hill with the parking brake set. Dumping air to submerge is like releasing the parking brake. Now, the inflator button becomes your brake on the way down, but treat it like you're on glare ice - little tiny taps to slow your descent and stop before hitting the bottom. When you want to ascend DO NOT add air. Use body position and fins to start upward. If you're neutral, any upward motion will make you postitive. Now the deflate button is your brake. Neither button should ever be like the gas pedal.No.

Very good description!! Explains it really well.

Xanthro

 

[H2Andy]

if you're using your deflate/inflate button like a brake you've waited too long.

an anology i like is the phrase "stay ahead of the plane" in flight training.

things happen so fast when you are going fast, that if you get behind the plane
(i.e. you are reacting to what's happening rather than making it happen) you are in danger.

in diving, it can be just as dire if you're faced with a run-away ascent. it can get nasty too if you sink like a ton
of bricks in the wrong place.

the key is to ANTICIPATE what the gas in your BC is going to do. on the way down,
you know you're going to sink like a rock, so start letting in a bit of air as you descend.

on the way up, you know you're going to shoot up like a rocket, so start letting
air out before it starts to happen.

also, the less weight you have, the less air you need, so bouyancy control will
be a lot easier if you use minimum weight and a LOT harder if you're over-weighted.

the smallest the corrections, the better. easy does it.

 

[The Kraken]

Beachdivequeenbelam wrote:

"1) get down about 15 feet on a platform(rock quarries are good for this) overweight yourself"

DON'T ADD MORE WEIGHT
You've already stated that you're "on the bottom". Being on the bottom makes it evident that you have enough, if not too much, weight to submerge.

If it's possible, on your next dive, break the weight that you are currently carrying into small increments, ie 1#, 2#, 3# weights. When your are on the bottom start removing weight a wee bit at a time until you reach the point that, with BC empty, you will start to slowly rise when you inhale and slowly descend when you exhale. Keep in mind that you need to give yourself a few seconds for the buoyancy change to take effect.

In another post someone recommended taking a weight belt with your current weight broken down into small weights. Hold the weight belt and slowly remove a weight until you reach the point which I described above.

Once you've reached this point, then you should work on your buoyancy at your safety stop depth with your tank at approximately 500 psi.

You will generally read on this board that you should be neutrally buoyant at 15' with empty BC and and Aluminum 80 at approx. 500 psi.

 

[Xanthro]

if you're using your deflate/inflate button like a brake you've waited too long.

an anology i like is the phrase "stay ahead of the plane" in flight training.

things happen so fast when you are going fast, that if you get behind the plane
(i.e. you are reacting to what's happening rather than making it happen) you are in danger.

in diving, it can be just as dire if you're faced with a run-away ascent. it can get nasty too if you sink like a ton
of bricks in the wrong place.

the key is to ANTICIPATE what the gas in your BC is going to do. on the way down,
you know you're going to sink like a rock, so start letting in a bit of air as you descend.

on the way up, you know you're going to shoot up like a rocket, so start letting
air out before it starts to happen.

also, the less weight you have, the less air you need, so bouyancy control will
be a lot easier if you use minimum weight and a LOT harder if you're over-weighted.

the smallest the corrections, the better. easy does it.

I think you and Dweeb has a history from reading other threads. He posted, treat it as if your were on ice. This is small little taps to slow you down. As on driving on ice, you can't start to slow down AFTER you've gained speed, you have to slow down in small increments BEFORE you normally would.

Both of your analogies work. The key is to slow down BEFORE you gain speed, whether descending or ascending. You know you are going to gain speed, you know that it takes time for the air to take affect in your BC, so you need to add/subtract air before your gain momentum.

Xanthro

 

[alemaozinho]

My husband and I have both logged in about 13 dives. We have begun our AOW because we were told that it would help our buoyancy. I can't seem to get it undercontrol. I seem to be on the bottom (20' down) or on the top. I've tried adding a bit more weight. I've been told to just keep practicing. My questions are:
What are some secrets that will help me get this under control? It's frustrating to both of us.
Am I ready to try deeper dives if I don't have this under control?

you,re propably weighted wrong and need to adjust your weights,then try in the pool until you get the hang of it.Read the portion(chapter) in you ow manual again to mentally rehearse again what you,ve learned in your ow class and finally dive dive a lot.Peace

 

[SueMermaid]

My contribution to the already excellent suggestions is simply to give any adjustment a longer time than you think is required. That is, when you tap air into your BCD, Wait. Wait some more. Take several breaths before you move to put more air into it.
The key is to relax, quit kicking and flailing your arms, and let every muscle go limp, like you are falling asleep. Feel the force. :japanese: Breathe in, rise, breathe out, fall. Do that again. And again.
Relax every muscle. Then your buoyancy and your weighting and trim will be more obvious to you.
This does, of course, take some practice. So the true key to it is to keep diving!

 

[lairdb]

This may help: the whole reduce-weight thing never really clicked for me (I understood the statement, but not the reason) unit I turned it around: the goal isn't to reduce weight. The goal is to reduce BC air; the tool for doing so is to reduce weight.

The BC/wetsuit/weight/water-column system is, in engineering terms, an inherently unstable system with positive feedback; a change in any direction (going higher or lower in the water column) will tend to accelerate.

The speed of the acceleration is set by the amount of air in your BC and in your wetsuit. If you have very litle air in your BC and no wetsuit at all, then you will accelerate very slowly and find it very easy to control, to regain a neutral state.

If you have a lot of air in your BC, you will accelerate quickly and have to make gross changes (dump lots of air) to reverse; this is the origin of the beginning diver yoyo.

The easiest-to-stay-neutral diver has the least possible air in his dive system. The diver carrying lots of lead must add lots of air -- which makes for a more unstable system.

 

[IowaDiver]

Each of these posts have been absolutely great help. (I started to write uplifting but I think that's a poor choice of words). First of all, it gave me hope that I can lick this. Secondly, I know that there in these suggestions are the answer for me. I plan to print these out and take them with me this weekend. We have planned dives on Saturday and Sunday in 25 feet of water. Not enough depth to get me in trouble but enough to work on my buoyancy. I also have a pool available to continue working on my buoyancy. This is a great community to belong to. You take care of even those of those who are still taking baby steps.
Thanks again.

 

[donacheson]

You don't need help with your buoyancy... you need help with your buoyancy control. This is an important distinction.

First there is a difference between static neutral buoyancy and dynamic buoyancy control. You can achieve perfect neutral buoyancy only to have it *disappear* the moment you start moving. Since most divers are constantly moving they never really know if they are neutrally bouyant or not because of the dynamic forces effecting them as they move through the water.

Secondly trim (body position in the water) plays a critical role in dynamic buoyancy control. At the base level understand that when you move forward through the water at the typical heads up body inclined up trim a lifting force is being generated. Your body is like an airplane wing moving through the water. To counter this upward lifting force most divers will be carrying extra weight. When they stop moving forward the lift is lost and they sink. They have the choice of adding air to their BC to stay off of the bottom, resume moving to generate lift or to just go ahead and settle to the bottom. Moving on from this level of experience the typical yo-yo diver will probably move into the rototiller level where they have given up on controlling buoyancy and are content to till along the bottom with their fins while their head is up by two or three feet. This is often the level at which divemaster has been achieved and it is not uncommon to see an accomplished rototiller *leading* a pod of yo-yos. Of course the only time the yo-yos can see anything is at the top of their swing when they can finally looking over the cloud of turbidity coming from the fins of the divemaster/rototiller.

Now I personally would suggest that you skip those levels of diivng expertise and move in a different direction. To achieve buoyancy control you will need to be properly weighted. Properly weighted you should be able to remain stationary in <10' water with minimal air in your tank (200~500 psi.) To ascertain your correct weighting you will need to go on a shore dive with an empty tank (200~500psi) and drop weights. Weight bags in a mesh belt are nice for this but you can also use hard weights in a bucket. Start ditching weight in 2# increments until you find that you can no longer stay down. Add back one 2# weight and you are now properly weighted.

Next you should practice swimming through the water in horizontal trim so that you are not adding positive or negative lift while moving. This will come easier than you might imagine if you dedicate your dive to geting the correct trim rather than just doing your normal dive agenda and *tacking* on trim practice.

And added benefit to correct weighting and trim is that you will move through the water much easier with much less drag and therefore your air consumption will improve dramatically. Also your CO2 retention will be much less.

That's generally good advice, Uncle Pug. I'd add (1) that proper weighting should be determined with an empty BC while breathing normally and (2) it can be achieved in a swimming pool with a full or near-full tank if the appropriate adjustments are made for sea/fresh water and the weight of air in the tank.

 

[beachdivequeenbelam]

Beachdivequeenbelam wrote:

"1) get down about 15 feet on a platform(rock quarries are good for this) overweight yourself"

DON'T ADD MORE WEIGHT
You've already stated that you're "on the bottom". Being on the bottom makes it evident that you have enough, if not too much, weight to submerge.

If it's possible, on your next dive, break the weight that you are currently carrying into small increments, ie 1#, 2#, 3# weights. When your are on the bottom start removing weight a wee bit at a time until you reach the point that, with BC empty, you will start to slowly rise when you inhale and slowly descend when you exhale. Keep in mind that you need to give yourself a few seconds for the buoyancy change to take effect.

In another post someone recommended taking a weight belt with your current weight broken down into small weights. Hold the weight belt and slowly remove a weight until you reach the point which I described above.

Once you've reached this point, then you should work on your buoyancy at your safety stop depth with your tank at approximately 500 psi.

You will generally read on this board that you should be neutrally buoyant at 15' with empty BC and and Aluminum 80 at approx. 500 psi.

yes he is correct about the weight and use the belt definetly!!!