buoyancy test..... HUH ?

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good recommendation spectrum about the the long inhale with slow exhale when you have to get over something not too high. Gonna start sessions this week and would rather use good breathing skills over having to throttle the bcd controls for minimal up and down movement when these situations arise.
 
herman:
You should float eye level with a normal breath AND ALL the air out of your BC. When you exhale you should start to slowly sink, no drop like a rock. Buoyancy control is a slow and deliberate process. Proper weighting is important but your understanding of the physics of buoyancy are much more important than being dead on with your weights. If you understand buoyancy you can dive with any BC or amount of weight, with in reason of course.
There are 2 basic problems I would suggest you consider.
Many divers tend to unconsciously fin when they are trying to descend feet first, they are finning up while trying to descend. To compensate for the finning divers will add more weight and dump the air in his BC, once the effects of the finning is overcome the diver starts to drop like a rock. To stop the decent a lot of air is added to the BC, in almost every case way too much air. About this time is when problem 2 comes into play. The simple fix is to stop finning and be properly weighted.
Problem 2 is more difficult to deal with. One of the most difficult concepts of buoyancy to learn is it's delayed response to changes. This is most likely one of the major problems you are experiencing. We are all use to things happening almost instantly, you press on the car's brakes and it immediately starts to slow down. This is not the case with buoyancy. When you add or remove air form your BC or take/let out a deep breath, it takes several seconds for the full effect of what you have done to take effect. New divers are way to impatient, they add air, nothing happens immediately so more air is added and maybe even a 3rd time. To make matters worse, each addition is bigger than before because "nothing is happening". Then the effects start to take hold and the diver starts to ascend. The accent starts to speed up, so the diver dumps some air, nothing happens, more air is dumped. About this time the delayed effects of dumping air starts to kick in and the diver is heading to the bottom fast. The result is yo-yoing up and down and having to constantly add and dump air. The solution is to be properly weighted and when you make a buoyancy adjustment, SLOW DOWN AND WAIT A FEW SECONDS to allow time for the effects of your change to take place. The art of buoyancy control is to know how much air to add/dump and when to do it to get the result you want.

Hi Herman :)
You described my problem perfectly :)
The continous yo-yo effect that causes all the frustration and confusion.

I will definately take you advise and apply it in a few pool sessions before heading out to sea again.
 
Aside from the correct weight, it is important to have the weight placed in the correct location(trim). This enables you to float horizontal. That way you are not swimming up or down all the time.
 
Yazrick:
Inflatting my BC to much made it difficult to stay in one place, and when I deflate my BC i sink like a rock.

That sounds like all-or-nothing inflation. Make small adjustments. Just a short pop on the inflator knob, then wait. If that's not enough, do it again. Practice fin pivots. That's where you learn basic buoyancy control.
 
Fin pivots are an ok place to start but move quickly to hovering. Learn to hold one spot in the water then add in some SLOW decents and accents using only breath control, 2 or 3 feet moves are fine. Hover in seveal different positions. Nothing teaches buoyancy better than dead still hovering. It's a skill I still practice every chance I get.
 
The root problem of over weighting is not often well explained, but I will try.

Many instructors will overweight divers so they can go down and learn skills and swim around enough to get certified. If you are lucky you will have been taught how to check your weighting and left with the blessing that "over time you will need less". This is true as your breathing relaxes and all that brand new neoprene begins to age with compression.

The problem with being over weighted is that you need to have more air in your BC at any given depth to be neutral. As you recall as you rise in the water the surrounding pressure will decrease and this will cause the air in your BC to increase in volume. The increased volume displaces more water and makes you even more buoyant. This causes you to rise and this cycle will repeat and rocket you to the surface if left unchecked. By having no more air than needed in your BC the air in your BC is less of a dynamic factor.

While I described the scenario the same holds true on decending. A heavy diver will begin to drop after swimming down just a foot or two. A well weighted diver may easily wander in a 10 foot range while remaining comfortably neutral.

You need to wear the weight you need (post 10) the trick is limiting tho just what you need.

What I am describing is in terms of a cold water diver in 7mm. Divers wearing lesser neoprene will experieince the same physics but the sensitivity will be less and the ranges of easy motion will grow.

Pete
 
ScubaStarwatcher:
<snip> If you have a full tank of air when doing this test, add a further 5kg of weight to make up for the fact that your tank will be lighter after the dive.
<snip>

(As a newbie to diving, I hope any experienced divers will correct any mistakes I've made in here :)

Just a small typo, but it may make a difference :wink:

You need to add about 5 lbs (not kg), or two kg to compensate for a mostly empty tank. This will make it easier to maintain your 15 ft/5 m safety stop depth.
 
For whatever it&#8217;s worth, I disagree that being over weighted makes a significant impact on bouyancy control. However it will increase your air consumption.

There are several tendencies of new divers that dramatically affect their bouyancy control or lack there of. The biggest one being the attitude, or angle, with which you move through the water. With a very few exceptions we move on land with a head up orientation. In the water we want to move with a horizontal orientation, but this seems very unnatural as first.

The tendency of new divers it to move through the water with a slightly heads up attitude. This creates lift and causes you to go up. To stop from going up you dump air to get enough negatively buoyant to overcome the lift. What happens if you stop moving forward? The lift is gone and you sink. So if you swim through the water this way, and almost all new divers (and some old ones) swim this way, every time you change speed, you sink or rise as the amount of lift changes.

If when moving forward you stop, do you sink? When you start moving from a stopped position do you go up? If so that is at least one and probably your biggest issue with bouyancy.

Another big factor is &#8220;I have to move my hands and feet syndrome.&#8221; If you are in a head up orientation and move your feet with fins on what is going to happen? It is going to created lift so unless you dump enough air to compensate you will rise. If you do when you stop moving your feet, you sink.

Proper weighting is important but it&#8217;s not the magic bullet to improve your bouyancy control. A much better way to improve you bouyancy control is to practice. A great drill is to adjust your bouyancy while moving forward then stop. Do you sink? If so you are swimming with a head up orientation and getting negatively buoyant to compensate. Another good thing to do is to get in the habit of stopping every time you change depth and adjusting your buoyancy before moving forward.

One last thing you can do is swim above the bottom and look behind you. If you are stirring up muck off the bottom, you are swimming with a head up orientation.

Hope this helps,
Mike
 
MikeS:
For whatever it&#8217;s worth, I disagree that being over weighted makes a significant impact on bouyancy control. However it will increase your air consumption.

<SNIP>
Proper weighting is important but it&#8217;s not the magic bullet to improve your bouyancy control.
<SNIP>

It's not the end all of diving to be sure. A few weeks ago my wife was trying something so I carried 4 extra pounds that dive in case she needed them and I didn't even know it was there. It was a shore dive that probably never got past 25-30 feet without checking my log. Physics says there is an effect but I suppose I was just compensating using what I learned in the prior 120 or so dives.

Now I have seen new divers that were able to shed 10 pounds of lead. To a new diver managing the bubble that offsets 10 pounds of needless weight in shore dive depths where a few feet is a big percent change of depth/pressure/volume/lift can do wonders in stabilizing them while they figure out the rest of their technique.

When knowledge, configuration and skill come together you can begin to dive.

Pete
 
MikeS:
For whatever it’s worth, I disagree that being over weighted makes a significant impact on bouyancy control. However it will increase your air consumption.........

Mike

For an experienced diver I totally agree but it's a lot more of a problem for an inexperienced diver. Having your BC inflated a lot (as a direct result of being way overweighed) means there is a lot of air to expand and contract. Move even a foot in either direction and you get quite a bit of buoyancy swing. This is esp true in shallow water where most new divers are. For us old timers, no big deal, we have a feel for the amount of air to add/remove and know instinctively how our buoyancy is going to react. We also know, understand and use varied breathing rhythms to help us deal with the issue, new divers have yet to learn some of these finer points of buoyancy control. Being close to correctly weighted helps the new diver gain the experience faster and helps prevent run away accents/descents.
 
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