What would be a safer weight next dive?

[Karibelle]

@Quero: I think what you've written might confuse some newer divers learning about buoyancy and Boyle's Law.

You think that what Quero said might confuse new divers?

 

[Bubbletrubble]

You think that what Quero said might confuse new divers?

@Karibelle: I'm a big fan of Quero's posts. I just thought that small part of her last post needed a little clarification that's all.

 

[Scuba_chicck]

I'm understanding the depth versus buoyancy better now - so thank you to everyone's posts.
I've sent out email looking for a lesson to beef up my weighting skills.
I think the most important lesson I have learned here is that even though you want to trust your instructors...the final choice of not (trusting them) - has to be made on occasion.
I was hedging on purchasing my own wetsuit but there are more points made here in favour of owning your own - so thank you again.
The dive did leave me questioning things, and it wasn't the best way to end my dive beginnings - but perhaps with the knowledge given here and working on weights before my next actual dive I'll be more confident again. Thx.

 

[Quero]

BT, thank you for that comment. You are right to a certain extent--when explanations get very simplified some details are lost, and this may lead to a less than precise technical understanding of the issues.

Nevertheless, the fact remains that if a diver maintains residual air in his or her lungs at a shallow depth, perhaps due to anxiety preventing the diver from exhaling fully, the attempt to stay neutral may become problematic and lead to an unplanned ascent. If that basic point is understood, it makes little difference, IMO, if the diver knows how much water the air in his or her lungs displaces. The questions of buoyancy and Boyle's law are intertwined when divers under stress fail to exhale fully. Divers who are calm and relaxed may very well achieve the full effect of a 10 pound displacement at depth as they can exhale fully, but if they are anxious and unable to exhale fully, they no longer can effect the entire 10 pound reduction in displacement in order to prevent an ascent.

You have explained things nicely, although in more detail than I would likely present to all but the more data-oriented divers. At any rate, it's good to have it all here as you never know who may be reading! So thanks again.

 

[Charlie99]

@Karibelle: I'm a big fan of Quero's posts. I just thought that small part of her last post needed a little clarification that's all.

I think the confusion is caused by the additional effect of air expansion in the BCD and neoprene rapidly expanding in the shallows. The initial effect of lung volume changes are identical at depth or in the shallows.

What's different at depth vs shallow is that the air in the BCD or the neoprene in the wetsuit change buoyancy more rapidly in the shallows. These changes kind of amplify the buoyancy changes initiated by lung volume, and make it feel like you lungs have larger effect in the shallows, even though the lungs themselves have the same effect independent of depth.

Did I succeed in confusing everyone?

 

[Bubbletrubble]

...if a diver maintains residual air in his or her lungs at a shallow depth, perhaps due to anxiety preventing the diver from exhaling fully, the attempt to stay neutral may become problematic and lead to an unplanned ascent...

I agree with this 100%.

You have explained things nicely, but in more detail than I would present to all but the more data-oriented divers.

In my opinion, I think students in basic OW class should be able to derive Boyle's Law from the ideal gas law. It's basic algebra that most people learn well before high school. But then again, maybe I'm just too nerdy.

 

[Quero]

I agree with this 100%.

In my opinion, I think students in basic OW class should be able to derive Boyle's Law from the ideal gas law. It's basic algebra that most people learn well before high school. But then again, maybe I'm just too nerdy.

It could well be that nerdy instructors have more strategies for explaining it in greater depth (pun intended) than those of us who are more right-brained.:daisy:

 

[Scuba_chicck]

g1138 - as I was rereading the thread I realized I never noticed the edit part of your question. To answer it:
I truly felt I was continually emptying my BCD on ascent, believe me - I was trying everything. I would typically have slowly kicked my way up, but certainly not this time.
I don't want to give the name of the company that certified me because I believe we were both to blame in that deep dive situation and I don't want to create any trouble for them. All I can say is it was in the Mayan in Mexico. The PADI class consisted of 3 or 4 pool dives, 4 ocean dives, the open water diver manual and quizzes and of course the videos. Lectures were not really a part of the lesson plan unless you want to count the various info taught in the pool etc.

 

[jar546]

Scuba_chicck,

Make sure you let us know how you made out with your adjustments and weighting. Thanks

 

[Scuba_chicck]

Okay, thanks I will.