Explain this

[sbl212]

Thanks for the replies!
I thought that while going deeper you had to add air to compensate. And I guess since he uses so little air that he doesn't need to add air to the BCD to compensate for the tank.
And yes,herman, he does wear a full wetsuit that is very old.

 

[DivemasterDennis]

Local DM's living on marginal incomes don't have the best gear and I agree with earlier comments that the bcd was likely not working properly so the DM used oral inflation, if any. As to use of air, time in the water is a big factor. I looked back at me first dives- I was good for maybe 40 minutes at 40 feet on an al80. Now I can double that, or more. Proper weighting, efficient movement, buoyancy and trim control, and EXPERIENCE together improve aior consumption rates.
DivemasterDennis

 

[Pin83]

It's not uncommon for proficient divers in warmer water to use their BC at the surface, and simply dump all the air from their BC on descent and dive with it this way throughout without needing to adjust. I used to before I was DMing, and I miss it! It's a mark of perfect buoyancy, which is largely a function of perfect weighting and experience. Now I carry extra weight for passing off to customers (inevitable), so I have some air in my BC throughout to offset it. This requires adjusting with depth, but it's not a major problem. I have had an inflator freeflow previously...diving with it disconnected is not a major deal, but not something to practice unnecessarily...

I dive with 15l steelies simply for the reserve volume, which was nice when I started DMing and had a higher SAC. I don't really need them now, but it moves weight onto my back anyway. A few month ago I forgot to top off my tanks before a trip, and discovered I had only 120bar going into the water. After a 45min dive, I came up with just under 80bar. The others in my group had breathed 12l allys down from 200bar to between 50 and 70bar. My air consumption is not normally this good, but it's interesting to see how long you can make air last if you have, once you're relaxed underwater (I'm 6'2" and 100kg, so I had to practically meditate to get my air consumption down that far!).

 

[Damselfish]

None of it is especially odd. Some people do have very low SAC rates, whether due to experience or smaller lungs or whatever. (I often come up with 2000# on a 3000# AL80, after an hour or more when most other people are long done.) His not connecting the inflator is probably due to something being wrong with it. An inflator is handy, but you can always orally inflate, that's what people did before someone came up with the power inflator. My husband was having trouble with his inflator last couple weeks and did most dives with it disconnected. No biggie, especially since he's one of those people who rarely puts air in his BC anyway. Experienced divers will adjust buoyancy a certain amount with their breathing volume, and in warm water without much exposure protection or weight there may not be much to adjust. If the DM didn't use much air, there's not much buoyancy swing from the tank to deal with. Wetsuit compression will cause a swing, but good chance whatever suit he's wearing is well worn and pre-compressed, again not causing much swing.

Fins, who knows. Maybe it's what he had, maybe he lost his and borrowed these, whatever. Maybe they rub his heels otherwise and he likes them on this way.

 

[BRT]

They all do... We did two scooter dives with a DM/Instructor a few years ago. We went into the water with full 3000 psi 80's. He went in with a 63. Mentioned he'd already used it for two dives that morning so he was down to about 1800. Coming out after the 2nd dive I noticed he had 1200 left...we were breathing fumes by then which called the 2nd dive.

It's just not right....

Unfortunately they don't all breath like that, but most do.

 

[fjpatrum]

As a new diver I've never needed air in my BC until I hit about 60 feet. I've done several dives with no BC at all and had no issues controlling my buoyancy as well as I ever do (which may or may not be great, depending upon who you ask). I don't see it as particularly strange that someone with 20 years of experience is diving effectively without a BC. It's not uncomfortable at all, even deeper, but it's harder to manage as you get deeper. (I never wear less than a 4/3 full suit so it can easily be done in less than that even deeper, depending upon your own lung volume and comfort level.)

SAC rates are what they are. Some people have phenomenal rates and others of us have moderately decent and still others have horrible rates. I don't worry about it too much, except for trying to plan my dives. It is what it is and I work within my limitations. I don't bother trying to compare it to others because this isn't a competition.

I wouldn't be comfortable diving with my full-foot fins only partially on, but I could do it, I think. I wouldn't make it a habit though.

 

[TSandM]

A "buoyancy compensator" is used to compensate for two things -- the weight of the air you are going to use up from your tank (generally no more than five pounds), and compression of your wetsuit. If you are diving in very warm water with thin suits, or no suit, you don't end up needing much air to compensate for compression at all.

A big framed person can easily manage a five pound buoyancy shift just by changing how they breathe; it's also possible that your DM put a tiny bit of air in his BC on descent, but then never needed to put in any more, because the dive generally got shallower.

Low SAC rates come with being a relaxed and very efficient diver. I just finished a dive trip where we had to record the ending pressure after each dive -- it was amazing to me to see the wide variation in what people used, doing just about the same dive.

 

[bullfroger]

He.probably was not wearing much of a wet suit, like a thin shortly. therefore not much change of buoyancy with the change in depth. Good lung capacity allowed him to use his lungs as a BC. good trim will really decrease your air consumption.pm

 

[Adventure-Ocean]

I dove over 10 years without a BC in warm tropical water. No weightbelt either. We used steel 72's then. I eventually went to AL80's with a wetsuit and weights but normally only used the BC to float on top. Over years of diving we get much more relaxed in the water and breathe much slower. If you have a reason you can hold your breath as long as you do not ascend. We did this often when a large fish came close. For me, breathing underwater is almost like zen. A controlled breathing rhythm that allows one to hover or cruise along at the same depth. Or trying for stealth in order to approach underwater life. It's about how much air you are pulling into your lungs and how you discharge the air. After years of breathing underwater, we get very good at it. Adventure-Ocean