Buoyancy problem

[TSandM]

Sandie, in your class, you've learned about pressure changes and their effects on air spaces, like your middle ear. You know that going from the surface to 33 feet will compress an air space to half its original volume. On the other hand, going from 33 to 66 feet just reduces the volume by a third. What this illustrates is that the PROPORTIONAL pressure changes are greatest in shallower water -- and the shallowest water anywhere is in the pool. When you are practicing buoyancy exercises in confined water, you are rarely terribly stable and often quite unaware of the depth changes you are undergoing. Even sinking a couple of feet can really tweak your ears, especially at the end of a class, when you have been doing multiple ascents and descents and your ears may not be clearing as easily as they were at the beginning.

When you try to Buddha hover, and fall over on your back, your head is undergoing a descent, even if your center of gravity isn't. Therefore, the pressure in your ears is changing, and you need to equalize. If you are anything like I was in my class, as you are falling over, you are thinking about just about anything and everything other than your ears, and it isn't until you have regained some kind of stability that you realize your ears hurt.

 

[Sandie7]

Sandie, in your class, you've learned about pressure changes and their effects on air spaces, like your middle ear. You know that going from the surface to 33 feet will compress an air space to half its original volume. On the other hand, going from 33 to 66 feet just reduces the volume by a third. What this illustrates is that the PROPORTIONAL pressure changes are greatest in shallower water -- and the shallowest water anywhere is in the pool. When you are practicing buoyancy exercises in confined water, you are rarely terribly stable and often quite unaware of the depth changes you are undergoing. Even sinking a couple of feet can really tweak your ears, especially at the end of a class, when you have been doing multiple ascents and descents and your ears may not be clearing as easily as they were at the beginning.

When you try to Buddha hover, and fall over on your back, your head is undergoing a descent, even if your center of gravity isn't. Therefore, the pressure in your ears is changing, and you need to equalize. If you are anything like I was in my class, as you are falling over, you are thinking about just about anything and everything other than your ears, and it isn't until you have regained some kind of stability that you realize your ears hurt.

Yes, absolutely, makes quite a lot of sense !

Ok, I've been reading your " Dive Journal" and now I know why I felt you understood me so well !

---------- Post added November 24th, 2014 at 10:48 PM ----------

Especially with someone new in the water. And as an instructor I would suggest you think twice about advising a student to "not bother" working on a skill the way their instructor teaches them unless they are being asked to do something dangerous. Far better to help them understand how to do it the way their instructor is teaching it... and then advise them that there are other ways as well. It's challenging enough for many students. They don't really need an anonymous stranger 10,000mi away - as well-intentioned as that stranger may be - undermining their instructor.

There's more than one way to demonstrate virtually any skill. As an instructor you can take advantage of the "teaching freedom" to use any/all of the fun, effective ways at your disposal if needed. It's as important - or more so - for the student to actually imprint the knowledge BEHIND the skill as it is the mechanics of the skill itself. A monkey can be taught to mime any one version of a skill. I'd much rather produce a student who can hover in any of handful of positions because they UNDERSTAND the skill... than a student who only knows one "by the book" way of doing it.

RPJ, wise words … and thank you, however I could never think bad of my (new) instructor. He has done so much for me already. I started with him in a “panic mode”, and much of his work has been directed to giving me confidence. And yes, much of that confidence is coming from his explaining “why” and from finding new (most of the time challenging and fun) ways of teaching …

Sandie-

What size steel tank...how high..and are you using trim weights?

Just a thought...

Bubs

It’s a 12 liter tank (don’t know how high). No trim weights. I didn’t use weights at all (wearing a shorty), except yesterday when we put on full wetsuits.
However, I heard that in the future I will be diving preferably with a 10 liters tank, as it seems I don’t use much gas …

I have some short video clips on my website that will show what others are talking about regarding more useful diving buoyancy and body position on this page: Coaching

Very good videos, thank you very much

Sandie from the first post i was wondering about what tank you are using. Now you have confirmed it is a steel tank. I and my other half have both had this problem. Let me describe it and see if it is familiar. As long as you are horizontal you are ok but when you stop and get out of trim you roll to your back. to fix this we had to put on more weight to force the use of more air in the wing. so long as you have air in the wing you stay belly down. with out air in the wing you are top heavy and it will naturally seek to be on the bottom. I suspect that you are not neutral at 4-500 psi at safety stop. Another factor is too buoyant of a wet suit. (your lift is under the tank and the weight is over the lift.) Another factor is how snug your rig is on your body. If it is too loose the tank moves from one side of your back to the other and combined with being top heavy you end on your back.

Yes, when I am horizontal I am ok, and with no problems (now). In my first classes (with other instructor) I was swimming unbalanced due to the tank moving. Now that has all been fixed. The suit is not the problem. I have been on a shorty, and only yesterday I wore a full wetsuit, the same thing happened. The problem is the tank … it’s so heavy ! I am sorry, but I don’t understand the concept of “more air in the wing” … too many new words in a foreign language I guess ...

 

[TSandM]

A BC has an air bladder in it, and the tank sits in the middle of the bladder. Depending on the type of BC, it may be that, if you put a lot of gas in the air bladder, it will wrap around the tank, creating a more stable configuration (since for the tank to go to one side, it has to push the air on that side DOWN, which the air doesn't want to do). Some BCs, particularly the jackets frequently used in classes, really don't have this phenomenon, because the fabric of the BC prevents it. "Wings" are air bladders that are sold to go with backplate rigs. They are a kind of back-inflate BC, so there is no continuous fabric going from your back to your front. This allows the side pontoons of the "wing" to wrap up around the tank the way I described.

In addition, if you overweight to do this, you can put the weights down toward your waist, creating a kind of keel to help stabilize you from rolling. But the price you pay is very unstable buoyancy, because all the extra air you have in your BC because of the weight you didn't need, is expanding and contracting as you go up and down, and requires very diligent management. New divers are rarely better off overweighted.

 

[RJP]

however I could never think bad of my (new) instructor. He has done so much for me already.

I wasn't suggesting that YOU were harboring ill thoughts...

[wink]

 

[LowDrag]

Sandie...any chance of seeing a pic of your BC?

 

[Sandie7]

I wasn't suggesting that YOU were harboring ill thoughts...

[wink]

Of course I wasn't ... was I ?

---------- Post added November 25th, 2014 at 02:50 PM ----------

Sandie...any chance of seeing a pic of your BC?

This is the one I have used in my last class:
Tusa

In the other classes, I had one from the school, don't know what it was ...

 

[LowDrag]

Of course I wasn't ... was I ?

---------- Post added November 25th, 2014 at 02:50 PM ----------



This is the one I have used in my last class:
Tusa

In the other classes, I had one from the school, don't know what it was ...

I started with a jacket also but soon went to a BP&W. When I did my skills work shop it was in my wing so I have not felt what good trim and buoyancy is like in a jacket style BC. I don't know what your area is like for diving but for us the BP&W is a good way to go. The stainless steel back plate adds to my weight so I can get it close to my center making it easy to distribute all of my weight around me. One thing to keep in mind is that I dive a dry suit and need extra weight at this point because of that and being a newer diver as well. I have trim weights on my upper tank area, in an integrated set of pockets, and on my upper shoulder D rings as well just to get my balance dialed in. It was a fun process of getting everything set up.

Good luck with your class and enjoy your diving!!!

 

[cooperscuba]

Frankly - while I have never found myself doing a Buddha hover on a "real" dive - it is kind of fun.

You be careful, telling people something diving related is fun! I teach people to Buddha hover, then horizontal, then vertical, then roly-poly (the idea being that the position doesn't matter, it's the lung control which is important). As for Buddha hovering on a "real dive", often do it on drift dives and often assume the position on course dives while observing students performing skills.

 

[RJP]

You be careful, telling people something diving related is fun!

There seems to be no shortage of instructors who think their role is "to put the F.U. in FUN."

 

[TSandM]

A while back, we did a drift dive with the Mike Severns group off Maui. Everybody in our group was experienced (I'm talking thousand or more dive experienced). One of the women did much of her dive in the Buddha position, just sitting and drifting and watching what was around her. It's the only time I've ever seen anybody use this position on a real dive.