Is buoyancy control more difficult with a thicker wetsuit?

[RonFrank]

Remember that your buoyancy changes the most in the first 33' of water.

You will also get heavy quickly wearing a lot more lead. So with 5lbs of lead you get about 5-lbs heavier at say 66ft, so a squirt of air in the BC. When you ascend to 10' you need to dump only 5 lbs of buoyant air on the way up. With 25lbs of lead you get about 25(-) lbs heaver at depth and that is what you will have to offset. When ascending you will constantly mess with the BC to dump that air. New divers can trap air and have uncontrolled ascents. If that happens then collect your thoughts and head back down to complete your dive.

A bunch of weight is a PITA but you get used to it. One of my favorite dive spots is S CA even if I dive dry there. Watching the sea lions play, diving in the kelp forests or checking out the Nudi's is quite magical even if the water is 49F.

 

[beanojones]

I still feel a frisson of annoyance when I am reminded of the fin pivot. In all three (!) of the classes I took wherein this maneuver was taught, I had a problem with it. The thing is, I tend to be a bit "foot light," if anything. So whenever I would try to do the fin pivot, I would end up hovering horizontal and going up and down with each breath, instead of angled with my fins touching the bottom, like they were supposed to be. It was so frustrating.

But, did they ever mention that horizontal was actually better (for real diving), and that the whole goal of the exercise was just to see that we could use breath control for buoyancy adjustment? (Which I was able to do.) NooOOOoooo. They just kept emphasizing that it was The Fin Pivot and that my fins needed to be resting on the bottom so that I could do a proper one. At that early stage, I simply understood what they said to be true (that I couldn't do a proper fin pivot), but missed that they were adhering to the "letter of the law" and not the spirit of it. Had I only known that it would be fine not to dive at a foot-down angle, and have my fins touching the bottom, I could have saved some frustration.

(Now that I'm past the rank beginner stage, I think I probably could get myself into the fin pivot position, but I haven't tried.)

Blue Sparkle

If it makes you feel better, they have made sure and eliminated the emphasis on "fin" pivot in the materials, and made it a general check/set neutral buoyancy skill.

It is an excellent transition exercise for understanding breathing control and buoyancy in confined water, but it seems best to get past it in the Confined water practice, because contact with the bottom in the open water is usually bad for a number reasons.

 

[FPDocMatt]

With 25lbs of lead you get about 25(-) lbs heaver at depth and that is what you will have to offset. When ascending you will constantly mess with the BC to dump that air.

I presume it's not the weight of the weights themselves which changes at depth, but the amount of air trapped in the wetsuit, which you're having to wear so much weight to offset. When you descend, the increased water pressure compresses the wetsuit, causing the air to get squeezed out of the suit...?

 

[Bob DBF]

I presume it's not the weight of the weights themselves which changes at depth, but the amount of air trapped in the wetsuit, which you're having to wear so much weight to offset. When you descend, the increased water pressure compresses the wetsuit, causing the air to get squeezed out of the suit...?

You got it.

The problem is the larger air bubble you have to start with, which gets bigger as you submerge and compensate. The larger the air bubble, the harder it is to control on the way back up, one missed air dump and you are off to the races, especially in the last 33'.



Bob
-----------------------------------------
I may be old, but I’m not dead yet.

 

[fisheater]

Sort of.

It's not squeezing the air out of the suit. It's squeezing the air (usually nitrogen) that's in the suit. I.e. making the nitrogen bubbles in the neoprene foam smaller.

These same bubbles "bounce back" on ascent. Seemingly all at the same moment, along with air you've added to the BCD at depth.


Sent from my iPhone using Tapatalk

 

[windapp]

My 7mm two piece is so bad at expanding in the last 20 feet. I have to look at my depth guage, and exactly 20 feet, dump my BCD or I shoot to the surface.

On the either hand, because I am used to the 7mm 2 piece, I find a 5mm one piece to be really easy for buoyancy control.

 

[soltari675]

It just takes a little practice. The water here is always 55 or below at the thermoclines so we regularly dive 5mm or dry suits. Once you get use to it, buoyancy becomes much easier. I actually went in just a swim suit in the pool once and had a hard time for the first few minutes because I wasn't use to it.

 

[FPDocMatt]

It's not squeezing the air out of the suit. It's squeezing the air (usually nitrogen) that's in the suit. I.e. making the nitrogen bubbles in the neoprene foam smaller. These same bubbles "bounce back" on ascent.

Yes, I worked it out after my post. I had forgotten that buoyancy is a matter of volume, not a matter of air. The extra air in your suit and in your BCD gives buoyancy by increasing your volume. The higher water pressure at depth shrinks this volume, decreasing volume and therefore buoyancy as your descend. As you ascend, it works in reverse; the decreasing pressure allows the air to expand, increasing your volume and therefore buoyancy as you ascend.

Why do you say that the air in the suit is usually nitrogen? Wouldn't it just be 78% nitrogen, 21% oxygen, like normal atmosphere?

 

[Lemna]

Why do you say that the air in the suit is usually nitrogen? Wouldn't it just be 78% nitrogen, 21% oxygen, like normal atmosphere?

Nitrogen gas instead of air is used to foam neoprene (Neoprene - Wikipedia, the free encyclopedia).