Solo with no BCD?

[John C. Ratliff]

The BCD also helps with the buoyancy shift as a full cylinder empties. Some experienced divers can manage the ~5# shift that occurs when an old-school PST 72 goes from 2,475 psig to 300 psig (say), just with proper weighting and his/her lungs.

However, managing the buoyancy shift as an OMS/Faber LP121/125 goes from 3,500 [sic] psig to 300 psig would not be possible for many divers, I think. (See what I did there!!??)

rx7diver

rx7diver,

Wouldn't that mean that the diver properly weighted needs that buoyancy at the start of the dive, not at the end?

SeaRat

 

[Subcooled]

In the mean time, would anyone here with more experience than me consider diving with just their drysuit and frame and no BCD?

Only if I had a way to drop weights before hitting 150 feet.
Hitting the bottom at 75ft and solving the issue there would be unpleasant but not deadly.

I have done it. I have been diving relying only on a drysuit for buoyancy. Lots of limitations. Lots of caveats. I always have a backup plan for how to resurface.

If your drysuit floods (and it really has happened to people) then you will need to reach the surface somehow - and stay afloat.
It's up to you to choose how to achieve that.
Crawling up a gentle slope is one option.
It takes time, so please carry enough air.
If there are walls, you'll need a plan.

I mean I know of some people that use the BCD as their buoyancy device anyway and leave they jacket empty.

That does not make any sense.
BCD stands for Buoyancy Compensator Device.
A jacket BCD is one option. A "wing" type bladder attached to a backplate is another option. A drysuit is a third option. Your fourth option would be a submarine.

If I stick to my self imposed limit of 10m what are your thoughts on this?

If you fail to maintain neutral or positive buoyancy then it does not matter how deep you are. You will end up at 3000 feet, and it's a one-way journey.

Depth is more relevant if you run out of air.

 

[MaxBottomtime]

Gallery of California Backpack Divers : 1999-2001

 

[rx7diver]

Wouldn't that mean that the diver properly weighted needs that buoyancy at the start of the dive, not at the end?

An OMS/Faber LP121/125 is rated at 125 cu ft @ 2,630 psig (= 2,400 + 10%) and is neutral in salt water when empty.
This cylinder cave-filled to 3,500 psig would hold ~165 cu ft. of free air/nitrox.
And at 300 psig, this cylinder would hold ~14 cu ft.
So, going from 3,500 psig to 300 psig is a buoyancy swing of ~12#--which is quite a large buoyancy swing to manage with only one's lungs. I am almost certain that this senior citizen can't.

rx7diver

 

[John C. Ratliff]

An OMS/Faber LP121/125 is rated at 125 cu ft @ 2,630 psig (= 2,400 + 10%) and is neutral in salt water when empty.
This cylinder cave-filled to 3,500 psig would hold ~165 cu ft. of free air/nitrox.
And at 300 psig, this cylinder would hold ~14 cu ft.
So, going from 3,500 psig to 300 psig is a buoyancy swing of ~12#--which is quite a large buoyancy swing to manage with only one's lungs. I am almost certain that this senior citizen can't.

rx7diver

I think you misread what I said; I was saying that the diver would need extra buoyancy, from a BCD, but that would be at the beginning of the dive, and not at the end. If the diver were still heavily negatively buoyant at the end of the dive, wouldn’t that mean that the diver was overweighted? In other words, he/she would need the BCD mostly at the beginning of the dive, when that 12 pounds of air was in the tank. At the end of the dive, not so much if correctly weighted.

SeaRat

 

[PBcatfish]

...
When I went through my NAUI ITC, we did not have any BCDs. Instead, we all work CO2 vests; now I cannot even buy a CO2 vest, as the manufacturers won‘t make them because some idiot tried to breathe off one and died, and they got sued. So that option no longer exist; you can only buy a snorkeling vest with an oral inflator now.
...

Those same CO2 gizmos still exist. They are used on inflatable life jackets now. If you can find a shop that does BC repairs (or inflatable PFD repairs) you can usually get a custom mod done to a BC & have the CO2 option added.

That CO2 cylinder is must useful when you jump off of a boat a little heavy, then find out that the nitwit, who double checked you air valve, turned it off rather than on.

 

[rx7diver]

I think you misread what I said; I was saying that the diver would need extra buoyancy, from a BCD, but that would be at the beginning of the dive, and not at the end. If the diver were still heavily negatively buoyant at the end of the dive, wouldn’t that mean that the diver was overweighted? In other words, he/she would need the BCD mostly at the beginning of the dive, when that 12 pounds of air was in the tank. At the end of the dive, not so much if correctly weighted.

SeaRat

Yes, @John C. Ratliff, I did misread what you wrote. Sorry. I provided an example (non/thin-wetsuitted diver using a very large capacity, neutral-when-empty cylinder) meant to illustrate when a BCD likely would be required by many (most?) divers. And, yes, I agree that the buoyancy provided by the BCD would be needed at depth at the beginning of the dive.

I am not terribly experienced diving sans BC--only a few years now, and only a couple dozen dives--but I can use my U.S. Divers/PST 72 and my OMS LP66, from full to "empty", just fine sans BCD. Each of these cylinders has a relatively small capacity. I haven't tried anything larger. In particular, I haven't tried--probably won't try--my Sherwood Genesis/PST HP120 or my OMS/Faber LP121/125 in fresh water.

rx7diver

 

[Celt]

I'd be happy enough to swim up my 8mm poseidon uni suit, but it's easier said than done. I dropped feet first into a large heat exchanger on a wreck in 50 metres, to cut out the copper worm. I caught the leg of my trilaminate bag suit on a piece of steel plate and put a large cut in it. By the time I shut the dump, dumped the air from my wing and pumped the suit I was flooded up past my waist. You won't swim up a flooded bag suit with a lot of underwear. I walked out a flooded northern diver 8mm neoprene when the shoulder zip went, working in a dock. You need to think carefully how you'll manage a flooded drysuit. It doesn't become a wetsuit.