Drysuit Buoyancy ????????????????????

[elan]

I do not think PADI is totally wrong when you use the dry suit "for buoyancy" with the trilam/crashed neoprene. At least in recreational department. Buoyancy compensation is required for the 1. air lose 2. suit buoyancy lose. the second is not existent with the thin dry suits as you adjust the volume of the suit with the depth. the first one depends upon how much air you consume. If you consume something in a range of 3-4lb of air which equals to 50-60 cuf some can compensate it easily with lungs. So you are 2 lb overweight with in the start of the dive and underweight 2lb at the end. So technically in this case you do not even have to touch the BCD button. So if you are properly weighted you should have no bubble to manage. So what they teach is correct with the above mentioned suits.

Thicker suits like 4 and 7 mill will lose buoyancy themselves so compensation for that would form a bubble in the suit and is better managed with BC imho.

"Eliminating the squeeze" is not technically correct. If you dive cold water the undergarments will stop to work properly long before you feel any squeeze, at least mine do.

Diving double tanks with stages is a different animal and if I read it right PADI mentioned that

 

[TSandM]

I don't weight myself or plan my dive for the gas I EXPECT to use. I weight myself for the gas that's AVAILABLE for me to use, so that, in the event that something delays me and I use more than I expect to, I will not also find myself having trouble controlling my ascent. Therefore, when I dive an HP130, I'm going down about 9 pounds negative at the beginning of the dive, and that's more than the gas required to loft my undergarment by quite a bit.

 

[elan]

I don't weight myself or plan my dive for the gas I EXPECT to use. I weight myself for the gas that's AVAILABLE for me to use, so that, in the event that something delays me and I use more than I expect to, I will not also find myself having trouble controlling my ascent. Therefore, when I dive an HP130, I'm going down about 9 pounds negative at the beginning of the dive, and that's more than the gas required to loft my undergarment by quite a bit.

Well if you dive that big tank then yes you have to put those lbs into the BC.

 

[pjones]

Thicker suits like 4 and 7 mill will lose buoyancy themselves so compensation for that would form a bubble in the suit and is better managed with BC imho.

My (Albeit limited) experience seems to be different than what you mention. If I understand you correctly than what your saying is: if the air in your suit is adjusted correctly than you will not experience a bubble as you rotate in the water.
What I notice is even with minimal air in my suit I aways notice the air rise to the shoulders if I invert to a standing position. My undergarments simply are not strong enough to withstand the crushing force that the water puts on the legs in that position and it flattens out under the force. This creates a bubble at the shoulders that I need to get back to my feet otherwise they get cold. I've never been able to completely eliminate the bubble without experiencing squeeze to some extent. Is there some way I don't know of to eliminate the bubble?

BTW TSandM: I like the new picture. I almost didn't recognize you at first until I read your signature ;-)

 

[W8less]

Again different gear, different techniques.

As a starting point suit/comfort, BC/buoyancy is sound advice but it is not dogma. You will find that the best skill to learn over time is to be adaptive.

Diving 3 different suits vulcanized (Viking) neo (Apollo) lam (Diving Concepts) all 3 suits have different capabilities and characteristics. I am partial to the neo dry on less than 100' dives and use it for primary buoyancy control. I like the fact that I can set/adjust the auto dump and be just fine on ascent. The lam suit I like on deeper dives and fill for comfort and use BC for buoyancy. The neo requires me to wear additional weight (12lb belt) and on hefty compression requires too much air to compensate. With the lam suit, I do not need a belt and feel that adjustments are more subtle. The dump valve on the vulcanized, even at full open will not dump fast enough to stay out of trouble, so I would never use it for primary buoyancy control.

If history is a valid indicator, than it is certain that you will have to learn new techniques to stay on top of evolving gear. What you are taught today with the exception of physiology and gas laws will be "old school" tomorrow.

 

[elan]

My (Albeit limited) experience seems to be different than what you mention. If I understand you correctly than what your saying is: if the air in your suit is adjusted correctly than you will not experience a bubble as you rotate in the water.
What I notice is even with minimal air in my suit I aways notice the air rise to the shoulders if I invert to a standing position. My undergarments simply are not strong enough to withstand the crushing force that the water puts on the legs in that position and it flattens out under the force. This creates a bubble at the shoulders that I need to get back to my feet otherwise they get cold. I've never been able to completely eliminate the bubble without experiencing squeeze to some extent. Is there some way I don't know of to eliminate the bubble?

BTW TSandM: I like the new picture. I almost didn't recognize you at first until I read your signature ;-)

Why do you need to invert to the standing position ? Stay horizontal, in this case the pressure difference will be measured in inches of water instead of feet and your undergarment will be dealing with it more successfully. Horizontal trim in a dry suit is even more important.

Another thing that I have noticed over the course of dry-suit diving is if you feel like adding air to stay warmer and that air forms a bubble it means you do not have enough undergarment or your undergarment is not as warm as you want it to be. Then either add another layer or find a warmer undergarment. It should not be bubbling but should take the space in between the fibers of the undies. Also if you crash your undies by not adding enough air in your dry suit on time as you descend they become colder and recover very slow to the original state.

 

[pjones]

Why do you need to invert to the standing position ?

I guess the short answer to this is because I'm tall, skinny and I rent gear. It seems that the best fitting seals are on suits one size too small. There is one suit that fits me but if I don't let them know soon enough in advance on occasion I'm out of luck. Sometimes I use a leash when I remember to request one and that fixes the problem. When I rent a suit my neck seal is most often too loose so for instance when I try to ascend/decend with my buddy I need to be in an upright position or I'm not able to see them because I can't rotate my neck without the suit leaking. If I'm taking pictures its hard for me to look at the view screen so I move into a horizontal stance for the same reasons. I plan to get a custom suit soon so I just deal with it (I only find it to be a minor inconvenience).

Another thing that I have noticed over the course of dry-suit diving is if you feel like adding air to stay warmer and that air forms a bubble it means you do not have enough undergarment or your undergarment is not as warm as you want it to be. Then either add another layer or find a warmer undergarment. It should not be bubbling but should take the space in between the fibers of the undies. Also if you crash your undies by not adding enough air in your dry suit on time as you descend they become colder and recover very slow to the original state.

Damn! Time for more layers I guess. I'll give that a try and see if it plays beneficial to my cause Thanks!

 

[TSandM]

Another thing that I have noticed over the course of dry-suit diving is if you feel like adding air to stay warmer and that air forms a bubble it means you do not have enough undergarment or your undergarment is not as warm as you want it to be.

I do not understand this statement at all. Whether the air is contained within the layers of fabric of my undergarment or not, it still has the ability to migrate to my feet if they are the highest point in my body, or to my arms if they are the highest point. This is what we are talking about when we talk about the "bubble"; gas can be moved from point to point in the suit, depending on position in the water. "Bubble" does not necessarily mean a bunch of air BETWEEN the undergarment and the suit, although there may be such gas. I'm not entirely sure how I'd know how much of the gas in the suit is actually in the garment and how much is outside of it.

 

[elan]

I do not understand this statement at all. Whether the air is contained within the layers of fabric of my undergarment or not, it still has the ability to migrate to my feet if they are the highest point in my body, or to my arms if they are the highest point. This is what we are talking about when we talk about the "bubble"; gas can be moved from point to point in the suit, depending on position in the water. "Bubble" does not necessarily mean a bunch of air BETWEEN the undergarment and the suit, although there may be such gas. I'm not entirely sure how I'd know how much of the gas in the suit is actually in the garment and how much is outside of it.

At some point when you try to add more air the undergarment does not take any more as the fibers are filled enough with gas so that air just stays in between them or between them and the suit. I can feel that as the free air moves much quicker. Say if you start completely squeezed and then will be adding some air the undergarment will be soaking air, at some point when it's saturated once you add air it will be in a free form and will be traveling to your highest point (say to your feet) much quicker. Depending upon the orientation in the column each particular part is compressed more or less, this is dynamic and changes upon the diver position. I can feel the free gas easily as it moves around very quickly.

 

[Tigerman]

The "correct" answer is simply that if you are weighed properly, you dont need to use either for bouyancy as removing the suit squeeze will put you where you want to be with regards to bouyancy.
The more complex answer is as others has said before.. Personal preference.

This of course changes if you go into tech diving (since youll carry more weight etc).