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.