Too heavy after a certain depth ?

[xyrandomyx]

I want to see a wetsuit explode!

Isn't that what happens when you put one in the microwave?

 

[Foxfish]

Maybe not that hard to imagine. I've seen people diving with two piece suits 7 + 7, so lets say an average of 10mm over 2 m2 of body area.
That's 20kg of water displacement.
Let's just suppose that the suit is well used and the neoprene is soft and they go deep enough for the 10mm to become 4mm, they just lost 12kg of lift. The average medium sized BC only lifts 12 or at the most 14 kg depending on the model/brand.
If they started overweight by a few kg, not hard when you're trying to sink a 7 + 7 suit, they can easily end up negative at depth even with the BC generating full lift.
But then there are a lot of divers out there that don't always pull the right dump valve and let a lot of water into their BC during the dive. So that theoretical 12 or 14 kg of BC lift is now 10 or 12 kg.

The numbers look realistic to me. The important number is the difference between the buoyancy force and the gravity force while on the surface.

---------- Post added February 11th, 2014 at 07:50 AM ----------

I want to see a wetsuit explode!

As your volume approaches zero at a depth approaching infinity your descent speed will approach the speed of light. It is hypothesized that at this mathematical singularity there will be a large explosion - and you will need to buy a new wetsuit.

If you don't believe me try it some time.

 

[kwinter]

You do not need to continue accelerating for the original problem to be true. You only need to be prevented from decelerating. Depending on the depth when you reach terminal velocity and the rate of flow from your power inflator, you could easily lose the ability to reverse the fall. As long as the rate of compression of the air cell equals or exceeds the rate of expansion, you would continue to fall. Of course the air supply to the wing would quickly be exhausted. The original hypothesis had nothing to do with dropping weights.


Please pardon any typos. Sent from my iPhone using Tapatalk

 

[Subcooled]

If properly weighted, dump all gas to become buoyant :reaper:

It can be a long way up...

 

[DCBC]

...they were saying that after a certain depth you can become so heavy that even your BCD cannot provide you with positive buoyancy. ...If anyone can clarify how this can happen, I would really appreciate it.

Before the B.C. can into existence (the early 70's) diver training was less focused on the technology (there wasn't that much) and more on in-water ability. Divers who found themselves with too much lead, quickly realized that this problem was compounded with depth.

I did my OW checkout in 1965 when I was 12 years old. At the time I didn't have hips and had a problem having to prevent my weight belt from slipping off my feet LOL. A dive to 100 FSW necessitated the diver to kick like hell to the surface. My first 130 foot dive caused me great anxiety, as I didn't think I had enough power in my legs to reach the surface. I saw many divers at that time drop their weight belt and pay the penalty for a rapid ascent.

The diving public became enamored with the advent of the B.C. Training courses in the early 70's incorporated buoyancy control as an import skill-set that was required for certification. Over the years, much of this has been lost, with the B.C./BPW being used as an elevator when someone wants to leave the bottom. Today N.B. is becoming more of a factor once again (although it's anything but a new skill-set).

So to answer your question, can depth cause you to sink even though your B.C. is fully inflated? Absolutely. A diver must keep in mind many factors when determining how much weight s/he should wear on any dive (part of the dive planning process). All equipment (not just the weight belt) may provide negative (or positive) buoyancy. Some of these are variable with depth and others do not.

Different B.C.'s / BPWs have different lift capabilities. In the event of failure, most of these unit can only provide negative buoyancy (with the exception of those with two bladders). Many divers carry redundant floatation (dry-suit, SMB or lift bag).

 

[agesilaus]

Around that same time period Sheck Exley mentioned in his book that he would carry a clorox bottle and blow air in or dribble air out to adjust his buoyancy.

 

[gcarter]

For the context we're talking about, up to say 100 m depth, what would be the variation in water density?

Water density changes with temperature. Viscosity changes with both temperature and pressure. Both affect the drag component of the equation. Point being, you are not dealing with a single variable model.

 

[Foxfish]

Water density changes with temperature. Viscosity changes with both temperature and pressure. Both affect the drag component of the equation. Point being, you are not dealing with a single variable model.

Feel free to demonstrate how this is likely to be a significant factor here. You could start by demonstrating you understand the formulations typically used to calculate drag and then quantifying how this is affected by the parameters you've nominated. And no I'm not talking about another cut and paste from Wikipedia.

 

[gcarter]

Feel free to demonstrate how this is likely to be a significant factor here. You could start by demonstrating you understand the formulations typically used to calculate drag and then quantifying how this is affected by the parameters you've nominated. And no I'm not talking about another cut and paste from Wikipedia.

It is as significant a factor as the nonsense you are spouting. It is as significant as buoyancy loss due to compression as it approaches zero.

As to Wikipedia? A ready source for an online cut and paste, no more. Would I be able to claim superior knowledge if I took a few textbooks off the shelf, typed a few quotes and their references? Given the stakes here it is not worth the effort. Nice red herring / implied slur though.

I decline your game.

 

[Foxfish]

You made some claims. I asked you to substantiate them. It's not a game. It's part of the discussion and exchange of ideas that is supposed to happen on a forum like this. You are obviously unable to substantiate even the most basic facts relevant to the claims you are making. You may be able to bluff a few ignorant people. The rest of us recognise you simply don't know what you are talking about. Thanks for sparing us another irritating and futile discussion.