Preferred redundant buoyancy when diving wet?

[Max Speed]

The optimal choice is that you would be diving a balanced rig in the first place. Meaning, in a single tank, there is absolutely no reason you cannot swim up your rig to a depth where your wetsuit has regained some buoyancy if you are properly weighted.<snip>Lets say that you are at the tail end of the dive (~1000psi in your al80) and you are starting to work your way up. Then the wing fails catastrophically (for example, you pull the corrugated hose off the elbow that is attached to the wing) and now the wing is venting all of the gas you have in there. Is there enough time to deploy a lift bag to use as redundant buoyancy? Or is it more likely that you will find yourself at 100ft before any corrective action can be taken?

Yes, there is plenty of time. I carry a pony when the floor is that far down as well as normally abiding by thirds. I can deploy the bag while heading down. I can normally fin hard enough to hold myself in place in the water column. I have practiced all those scenarios. And to go back to your first point; I estimate that wet suit compression causes a loss of about 20 lbs pf buoyancy by 100'. Do you dive cold water in a wetsuit? This buoyancy change is common for everyone I dive with. How are you gonna "balance" that and still descend in the first place?

 

[Adobo]

Yes, there is plenty of time. I carry a pony when the floor is that far down as well as normally abiding by thirds. I can deploy the bag while heading down. I can normally fin hard enough to hold myself in place in the water column. I have practiced all those scenarios. And to go back to your first point; I estimate that wet suit compression causes a loss of about 20 lbs pf buoyancy by 100'. Do you dive cold water in a wetsuit? This buoyancy change is common for everyone I dive with. How are you gonna "balance" that and still descend in the first place?

1) How do you go about figuring that you lose 20lbs of lift? And if this is true, why not use a drysuit? It is cold enough to wear a 7 mil but not cold enough for a drysuit?

2) For comparison, I need ~13lbs of lead when diving my drysuit, 400gram undergarment, 13mil hood, steel backplate and a neutrally buoyant tank like a PST HP100. That would mean that I would need about 17 or so lbs. of lead if diving an al80. So what you are saying is that you need about 5 lbs more lead to sink your wetsuit than what I need for my drysuit + the thickest undergament that is available in most dive shops. Does that sound right to you?

(Incidentally, the last time I dove a 7 mil farmer john, I used about 20lbs of lead. At the beginning of the dive, I could barely keep my head above water even with my wing fully inflated.)

3) Presumably a wetsuit will have lost 33% of it's lift at 15ft. You are saying that you are neutral at the safety stop with no air in your wing but you cannot swim a rig up when that same wetsuit has lost 75% of its lift at 100ft. Is that right?

 

[Max Speed]

1) How do you go about figuring that you lose 20lbs of lift? And if this is true, why not use a drysuit? It is cold enough to wear a 7 mil but not cold enough for a drysuit?

Now you're making me work! That was a "seat of the neoprene" number based on how much air I had to shove into a 27lb lift wing I used to use. A quick search of the internet reveals the following from Scuba board and Rodales:

Wetsuit buoyancy loss - how much? [Archive] - ScubaBoard
"Most divers know that neoprene compresses with depth, losing buoyancy the deeper you go. But you might be surprised by how much it compresses. Most lose half their buoyancy in the first 33 feet, two-thirds by 66 feet and nearly all of it by 100 feet. At that point, 7mm neoprene foam has become solid neoprene less than 2mm thick. In this case, the buoyancy shift between the surface and 100 feet can be more than 20 pounds from the wetsuit alone."

Or this from DAN:

DAN Divers Alert Network : The Ups and Downs of Buoyancy Control

It looks like you lose at least 4/5 of your buoyancy at 130'. It takes about 26 lbs to sink me with the suit on (includes an allowance for the backplate) and no weight to sink me in the pool with a jacket BCD and shorts on. So doing the math that works out to about 21 lbs lost buoyancy which is pretty close to my estimate.

I use the same 22 lbs weight on the belt when using a Trilaminate dry suit with fuzzy underwear. I use about 45 lbs when diving a non-compressed neoprene dry suit with the same fuzzy undies.

No, I can't swim it up. Maybe if I was breathing my last 200 psi I would find the strength...

 

[danvolker]

Now you're making me work! That was a "seat of the neoprene" number based on how much air I had to shove into a 27lb lift wing I used to use. A quick search of the internet reveals the following from Scuba board and Rodales:

Wetsuit buoyancy loss - how much? [Archive] - ScubaBoard
"Most divers know that neoprene compresses with depth, losing buoyancy the deeper you go. But you might be surprised by how much it compresses. Most lose half their buoyancy in the first 33 feet, two-thirds by 66 feet and nearly all of it by 100 feet. At that point, 7mm neoprene foam has become solid neoprene less than 2mm thick. In this case, the buoyancy shift between the surface and 100 feet can be more than 20 pounds from the wetsuit alone."

Or this from DAN:

DAN Divers Alert Network : The Ups and Downs of Buoyancy Control

It looks like you lose at least 4/5 of your buoyancy at 130'. It takes about 26 lbs to sink me with the suit on (includes an allowance for the backplate) and no weight to sink me in the pool with a jacket BCD and shorts on. So doing the math that works out to about 21 lbs lost buoyancy which is pretty close to my estimate.

I use the same 22 lbs weight on the belt when using a Trilaminate dry suit with fuzzy underwear. I use about 45 lbs when diving a non-compressed neoprene dry suit with the same fuzzy undies.

No, I can't swim it up. Maybe if I was breathing my last 200 psi I would find the strength...

And from this people should get that if it is cold enough to need a neoprene wetsuit that is 7 mil thick at the surface, then at 100 feet they might as well be in a lycra skin....so the choice of the thick wetsuit for deeper diving fails in SO MANY areas, that this thread should not last much longer

 

[Adobo]

Now you're making me work! That was a "seat of the neoprene" number based on how much air I had to shove into a 27lb lift wing I used to use. A quick search of the internet reveals the following from Scuba board and Rodales:

Wetsuit buoyancy loss - how much? [Archive] - ScubaBoard
"Most divers know that neoprene compresses with depth, losing buoyancy the deeper you go. But you might be surprised by how much it compresses. Most lose half their buoyancy in the first 33 feet, two-thirds by 66 feet and nearly all of it by 100 feet. At that point, 7mm neoprene foam has become solid neoprene less than 2mm thick. In this case, the buoyancy shift between the surface and 100 feet can be more than 20 pounds from the wetsuit alone."

For a balanced rig, you do not weight yourself at the surface. You weight yourself at 10ft or even 15ft. If you were neutral at 15ft without any air in your wing, you are neutral with your wetsuit having lost about 33% of its inherit lift. At 100ft, your a gas bubble is 1/4 the size of what it would be at the surface. Or put a different way, your wetsuit will have lost 75% of its inherent buoyancy at 100ft. The amount of lift lost by going to 100ft vs. being neutral at 15ft is about 40% of the lift capacity of your wetsuit.

Or this from DAN:

DAN Divers Alert Network : The Ups and Downs of Buoyancy Control

It looks like you lose at least 4/5 of your buoyancy at 130'. It takes about 26 lbs to sink me with the suit on (includes an allowance for the backplate) and no weight to sink me in the pool with a jacket BCD and shorts on. So doing the math that works out to about 21 lbs lost buoyancy which is pretty close to my estimate.

I use the same 22 lbs weight on the belt when using a Trilaminate dry suit with fuzzy underwear. I use about 45 lbs when diving a non-compressed neoprene dry suit with the same fuzzy undies.

No, I can't swim it up. Maybe if I was breathing my last 200 psi I would find the strength...

At 500psi on an al80, your rig is about 5lbs lighter than it was at 3000psi. If you can't swim up a balanced rig with only 500psi on an al80, it might be time to consider getting on a treadmill.

A lot of the information you are including is not pertinent. This is really a simple problem solved with simple solutions. You have a drysuit. For deep dives, use it. Your wetsuit is pretty much useless for thermal protection at 100ft anyway.

If you have to use a wetsuit for whatever reason, its all the more important to go learn how to balance your rig properly. If after balancing your rig properly you still feel like you cannot swim yourself up with a failed wing, put some of that 22lbs of lead on a weight belt.

Done.

 

[dumpsterDiver]

For a balanced rig, you do not weight yourself at the surface. You weight yourself at 10ft or even 15ft. If you were neutral at 15ft without any air in your wing, you are neutral with your wetsuit having lost about 33% of its inherit lift. At 100ft, your a gas bubble is 1/4 the size of what it would be at the surface. Or put a different way, your wetsuit will have lost 75% of its inherent buoyancy at 100ft. The amount of lift lost by going to 100ft vs. being neutral at 15ft is about 40% of the lift capacity of your wetsuit.




At 500psi on an al80, your rig is about 5lbs lighter than it was at 3000psi. If you can't swim up a balanced rig with only 500psi on an al80, it might be time to consider getting on a treadmill.

A lot of the information you are including is not pertinent. This is really a simple problem solved with simple solutions. You have a drysuit. For deep dives, use it. Your wetsuit is pretty much useless for thermal protection at 100ft anyway.

If you have to use a wetsuit for whatever reason, its all the more important to go learn how to balance your rig properly. If after balancing your rig properly you still feel like you cannot swim yourself up with a failed wing, put some of that 22lbs of lead on a weight belt.

Done.

DONE??? WTF... A diver needs to be weighted so they do not float up from 15 feet.

At first you seem to fail to understand how much bouyancy is lost from wetsuit compression, then someone gives you some references, and you say it is irrelevant and then you spout off your own numbers which seemed to be based on the assumption that a wetsuit compresses the same as a bubble of air????

Then to top it off, you say nobody should use a thick wetsuit?


You then go on to say that a thick wetsuit is useless at 100 feet. More BS. A wetsuit is compressed and looses insulation at depth, but it is more than adequate for cool water diving, especially if the water is above maybe 45 or 50 degrees and the duration is moderate. Not everyone has the money for a dry suit and 7 mm suits have worked for divers in the recreational depths (and deeper) for over 40 years.... Give me a break!

 

[Adobo]

DONE??? WTF... A diver needs to be weighted so they do not float up from 15 feet.

At first you seem to fail to understand how much bouyancy is lost from wetsuit compression, then someone gives you some references, and you say it is irrelevant and then you spout off your own numbers which seemed to be based on the assumption that a wetsuit compresses the same as a bubble of air????

Then to top it off, you say nobody should use a thick wetsuit?


You then go on to say that a thick wetsuit is useless at 100 feet. More BS. A wetsuit is compressed and looses insulation at depth, but it is more than adequate for cool water diving, especially if the water is above maybe 45 or 50 degrees and the duration is moderate. Not everyone has the money for a dry suit and 7 mm suits have worked for divers in the recreational depths (and deeper) for over 40 years.... Give me a break!

Reading comprehension is key. Absent that, you will be left feeling like you have no idea what is going on.

 

[Crush]

I estimate that wet suit compression causes a loss of about 20 lbs pf buoyancy by 100'.

My lift wing used to be #24. With a 7 mm two-piece FJ and gloves and hood, I was slightly negative at 90 ft. My weighting was such that, at the surface with an empty wing, I would sink with a deep exhalation.

And from this people should get that if it is cold enough to need a neoprene wetsuit that is 7 mil thick at the surface, then at 100 feet they might as well be in a lycra skin....so the choice of the thick wetsuit for deeper diving fails in SO MANY areas, that this thread should not last much longer

danvolker, you are obviously a better and much more experienced diver than I am. However, I have dived a 7 mil wetsuit in cold water. Perhaps you have as well. In describing the insulative properties of such a wetsuit at 100 ft as "lycra" you are demonstrating some of the negativity, (perceived) superiority, rigid mindset and thought patterns that cause people to despise DIR/GUE divers. For you, a 7 mil wetsuit on a five hour dive would be hypothermic. For the majority of us, that suit for a short dive at 100 ft on a single 100 would be adequate. Forgive me if I misunderstood your post..

It is all about context. We don't all have to be marathon runners to enjoy jogging.

 

[Adobo]

My lift wing used to be #24. With a 7 mm two-piece FJ and gloves and hood, I was slightly negative at 90 ft. My weighting was such that, at the surface with an empty wing, I would sink with a deep exhalation.



danvolker, you are obviously a better and much more experienced diver than I am. However, I have dived a 7 mil wetsuit in cold water. Perhaps you have as well. In describing the insulative properties of such a wetsuit at 100 ft as "lycra" you are demonstrating some of the negativity, (perceived) superiority, rigid mindset and thought patterns that cause people to despise DIR/GUE divers. For you, a 7 mil wetsuit on a five hour dive would be hypothermic. For the majority of us, that suit for a short dive at 100 ft on a single 100 would be adequate. Forgive me if I misunderstood your post..

It is all about context. We don't all have to be marathon runners to enjoy jogging.

Maybe it is I who has some reading comprehension issues. What does this topic have to do with DIR/GUE?

 

[Crush]

Maybe it is I who has some reading comprehension issues. What does this topic have to do with DIR/GUE?

The topic has nothing to do with DIR/GUE. My comment (perhaps misinformed) deals with the long-standing issue of why, despite their excellent and the truly excellent training they deliver, DIR/GUE continue to be maligned by non-practitioners. In a word: condescension. Again, if DV was being wry and I missed his humour, I apologize. But, to cr@p on someone's choice of gear (in this case, a wetsuit) because one is applying the standards of a five-hour deco dive to a 20 minute excursion smacks of wanting so strut one's superiority before the "ignorant" masses.