Preferred redundant buoyancy when diving wet?

[Thalassamania]

Again...the last thing you want to do is to ditch all your weights as others have previously mentionned. Doing so is the best way to transform a mere malfunction into what could become a full blown emergency

I don't see it that way, but then I've done quite literally thousands of buoyant ascents in the classes I've taught. I also would not expect any of my students to have any problem preforming one.

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?

With a hard bottom, who cares? Take your time. Now ... with no bottom, that's a whole 'nother story. Then I'd drop the damned weightbelt.

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?

With good rubber and a 7 mil or 9 mil farmer john suit loosing 20 lbs of lift is fairly easy. Good chart on the subject in the Univ. of Michigan Research Diver Manual, page 132.

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?

For dry suites I wear about 23 lbs with my Viking, a little more with my DUI and 36 with my Polaris (Rubatex 231). A full 7 mil Rubatex 231 farmer john wet suits takes me 32 lbs.

(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 inflated.)

Then perhaps you were wearing too much weight, these new neoprenes are not very warm and don't have as much buoyancy at the old Rubatex.

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?

I can't speak for the new rubbers, my suit is down a third at about 30 feet and at 100 feet is down a little more than half.

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."

My shift at 100 feet is about 15 lbs, which is no biggie, cause I can shift my buoyancy that much just by moving where I center my breathing in my cycle.

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 130 feet I'm only down two or three lbs. from 100 feet.

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

Damn new materials ain't worth crap when it comes to warmth.

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.

I've been under the Arctic ice, down to 150 feet, in a custom 7 mil wetsuit. I was quite comfortable, and water does not get any colder than that. The trick is skin two sides for tight feet and good sealing. Reduced to a lycra skin my suit was not.

 

[DevonDiver]

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

To be fair, I don't see that advice as 'rigid thinking'.... more like 'best practice'.

There's a bunch of worthy reasons why a drysuit would be ideal for the dives/conditions discussed. Not so many reasons to support using a wetsuit.

But.... if a wetsuit is what you have, and you can't justify the cost of upgrade, then that is all the justification you need to dive wet. You'd just need to apply some further thought into the issues that it raises.

 

[Max Speed]

Getting wet while swimming around underwater! I don't know what i was thinking...

 

[danvolker]

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.

Crush,
I used to dive the Hole in the Wall nearly every weekend....this was in a thick wetsuit in winter...this dive would be typically spanning 112 to 145 feet deep, each dive, for about 20 minutes, then slow ascent and short deco stop.....If there was any thermocline at all, I would freeze....the bouyancy of the suit dropped a lot, but that I could deal with using either BC or swimming..the only way I ever got so that this dive would not make me cold on a day with a strong thermocline, was wearing a dry suit....the difference was awesome Warm, comfortable......slower and more drag which I did not relish, but a good trade off to avoid getting cold. When we started doing "much deeper" dives in Palm Beach, it was not really an option. The liklihood of hitting very cold water any day you go out, on any drop below 200 feet was just too high....

I get preferring to use a wet suit...I use my Beuchat 2.5 ml wetsuit as long as I can...it is slick, does not effect bouyancy much more than a no suit at all, and it is not the big prep and everything else of the DS.

But on the deeper stuff, we are going there because we can see incredible sights we don't get on shallow dives....we have plenty of bigger challenges in doing these deeper dives, and to me, it makes sense to minimize those challenges where you can....Even on the 100 to 140 foot stuff, still dives a recreational diver with good skills could be doing, this will come strongly into play

 

[Crush]

DanV,

I agree with drysuits being awesome in cold water, both during a dive and between dives.

Cheers

 

[Crush]

To be fair, I don't see that advice as 'rigid thinking'.... more like 'best practice'.

I may well have mis-read the statement. However, while the intent may have been to put forward "best practices" the product (to my mind) portrayed something different. It may be "best practice" to use a paint roller, but for small jobs a brush is perfectly satisfactory.