Vintage Tank Buoyancy

[SurfLung]

- Watching Sea Hunt episodes, I see Mike Nelson diving his shorty doubles with no wet suit and even wearing a weight belt. In fact one scene showed an extra weight belt weight attached between his doubles. I would think he'd be sinking like a rock.
- My modern experience diving with no wetsuit buoyancy is that I'm barely neutral with an aluminum 50 on my back and no weight belt. When I put my compact steel 80 cf tank on, with no wetsuit and no weights, I sink. If I put on my 2mm wetsuit, I'm neutral at the surface with this compact steel 80 and no weights BUT, beyond 10-12 feet deep, I sink. My Oxycheq traveler wing is the only way I can dive neutral with no wetsuit for buoyancy.
- So my question is: Were vintage tanks designed for buoyancy closer to neutral?

[Herman]

You need to eat something and build some bioprene, it floats.

My twin 38s (early 60s vintage) with manifold and a tublar steel frame are about 2 lbs negative full and just shy of 2+ when empty - about the same as an al80. I dive either with no wetsuit or extra weights with near spot on weighting. I have to add about 4 to 5 lbs of weight in salt water.
Maybe Mikes weights were also balsa.

[Nemrod]

Frankly, this is a learned skill. There have been numerous threads here and on scubyboard about the how to of diving sans BC but it is a worthy subject. I am not among the aluminum 80 haters, though slightly more range shift than a steel 72 becoming approximately four pounds positive near empty that is just not enough to exclude them from being a useful no BC tank. The aluminum 64 very closely approximates the steel 72 and of course, the ubiquitous steel 72 was nearly perfect.

Depending upon your diving and exposure suit needs, we weighted for 15 to 20 feet neutral and we SWAM down until our suits compressed enough to become actually slightly negative at the beginning of the dive (once past 15 or 20 feet). Towards the end of the dive, yes, one might become slightly positive and that is why God placed stones on the bottom for us to pick up and carry about as auxiliary weight.

Safety stops, well, what is a safety stop, no need to hold at 15 feet because we did not do safety stops, we ascended at 60 fpm direct.

Your lungs are a mini-BC and can be used effectively to fine tune bouyancy.

The neoprene used in suits in the day was Rubatex G231 nitrogen gas blown sheet. It was very resistant to compression at depth providing a more uniform buoyancy at depth after an initial set.

We SWAM around at depth, often slightly negative.

Then we SWAM back up, often still negative at the beginning of the ascent, but not as much so since our tanks were now at 300 psi and the reserve had been deployed. As we ascended the suit would regain buoyancy and assist ascent, however, the neoprene would not fully regain it's normal thickness for several hours and in fact, a suit would go through a break in period and sort of crush down, reducing the initial buoyancy.

These skills were TAUGHT during the often long and arduous courses given in the earlier days and as already mentioned are skills that are still useful today, to bad they are no longer taught.

Of course, the thinner the suit or no suit makes no BC diving easy with aluminum 50s, 64s, 80s, steel 72s etc. Yes, the good old steel 72 as a single tank rig is where you need to start. Perfect neutrality throughout a dive is simply not possible, we SWAM through our dives, a BC now makes it possible for divers (if one can use that word loosely) to descend, hover around and ascend with push button ease and yet, somehow they still manage to crash into every coral head and beautiful sea whip on God's blue earth.

I am not sure that the filmed action in Sea Hunt is accurate. They could have been horribly weighted, they spend a lot of time kicking up the bottom and making mayhem of the bottom. And the arm swimming is a hoot.

Nem

[DaleC]

With a St 72 on a abs backpack and a 3/2 one piece wetsuit I can maintain buoyancy with 2-3 lb's of lead. I can also dive with no lead but fight a bit of pos. buoyancy at the end of the dive. I get the same performance from my twin 40Al's on a flat Al plate. I can hang neutral throughout my dive pretty easy.

I can also dive sans BC with my drysuit and thin undergarments with 12lb's of lead, using just the DS for lift without creating too big a bubble. Near the end of the dive I have almost all the air out of it though. Double 72's are pushing it a bit though I can still do it (bigger bubble).

No exposure protection? The only reference I have is pool diving in which I wind up being slightly negative with a St72 and no weight. I have to keep finning in that situation. I've never done an actual OW warm water dive, vintage or modern - though I did swim in a pool in Anaheim once

[scubasteve59]

No need for lead....I find a steel 72 with neoprene vest or shorty suit perfect for trim with absolutely no weights or BC. Regularly dive to 100+ in this config. It's a beautiful thing to experience.

[SurfLung]

The aluminum 64 very closely approximates the steel 72 and of course, the ubiquitous steel 72 was nearly perfect.

- Interesting about the 64 cf aluminum tanks. I've been diving 53 cf aluminum tanks but on vacation last year I had to take 64's on rental. I was diving with no wet suit in salt water and the 64 was a very comfortable tank... Once I had my weights set up on the first day I had no buoyancy issues the rest of the week. But, I suppose with no wet suit to compress, buoyancy stays pretty simple no matter what the tank.
- Herman, thanks for the vote of confidence but, I've got plenty of "Bioprene"... (Lost 30 lbs of it so far and seek to lose another 30... )

[floatingpi]

With my triples I have to use some weights with my hydroglove. I use both about 4 and 6 lbs of lead, as I get two dives off my triples. Four on my first dive and six on my second. This is of course fresh water as well.