Air Consumption Curiosity

[Tigerman]

And that would make for a very shallow average depth.. which was boulderjohns point, and mine..


Also just to do 90 minutes at 20ft on half an al80 (which would be 39 cuft, the al80 only is 77 full), let alone any part of the dive deeper, your sac need to be running at .27 cuft/min which Id think would be unusually low (or exaggerated).

 

[bradells]

And that would make for a very shallow average depth.. which was boulderjohns point, and mine..

Also just to do 90 minutes at 20ft on half an al80 (which would be 39 cuft, the al80 only is 77 full), let alone any part of the dive deeper, your sac need to be running at .27 cuft/min which Id think would be unusually low (or exaggerated).

Exactly!

I do well when when looking for seahorses and waiting for mermaids ....

BRad

 

[LeadTurn_SD]

I'm a large male, 6' 4", 260 lbs. I run .7 - .8 on "active" dives, 1.0 if I'm "working" (strongish surge), less if I am just cruising, and my lowest consumption rate is when I am solo... something about diving solo leads to a "zen" kind of experience super relaxed, not worried about leading a dive, just myself.

My wife is 1/2 my weight and 9 inches shorter, far less muscle mass.... her SAC rate seems to be in negative numbers sometimes!

Don't worry about air consumption. We all need what we need. That is why God created larger tanks... .

Best wishes.

 

[Tony387]

And that would make for a very shallow average depth.. which was boulderjohns point, and mine..


Also just to do 90 minutes at 20ft on half an al80 (which would be 39 cuft, the al80 only is 77 full), let alone any part of the dive deeper, your sac need to be running at .27 cuft/min which Id think would be unusually low (or exaggerated).

I was feeling really bad about my SAC, there for a minute.

Sent from my SCH-I545 using Tapatalk

 

[Max Speed]

Diving wet in 39F to 42F dark water, can't find the wreck dive 0.9

Hanging around in Florida Keys warm water 0.45

Dragging myself out of a siphon 2.4 !

 

[Doc Harry]

Dragging myself out of a siphon 2.4 !

That's why I don't dive siphons!!!!!!!!!!!!!!!!

 

[EFX]

Check your trim. You may be swimming horizontally but using more air to keep you there and not realizing it. That was my situation when to my surprise during a buoyancy class I was told to relax and went vertically head down. You said you were able to hover but small movements may be keeping you horizontal. Try being absolutly still and see where you go. A good check for horizontal trim is to put your chin on your chest and look underneath and behind you. If you see the bottom you're not horizontal.

Another issue that can increase gas consumption is unnecessary use of the BC. I've seen some beginning divers go vertical to check their SPG. While reading it they're finning and slowly ascending. When finished reading their SPG they have to let air out of their BC to get down and then add air to go neutral at depth. Be conscious of all movements and strive to eliminate all unnecessary movement and this will help to reduce gas consumption.

 

[boulderjohn]

Another issue that can increase gas consumption is unnecessary use of the BC. I've seen some beginning divers go vertical to check their SPG. While reading it they're finning and slowly ascending. When finished reading their SPG they have to let air out of their BC to get down and then add air to go neutral at depth. Be conscious of all movements and strive to eliminate all unnecessary movement and this will help to reduce gas consumption.

This sort of thing happens more than people might expect, and it can lead to an additional problem.

The diver who does what is described here will keep getting frustrated by this problem and will look for a solution. "I keep floating up to the surface!" they will complain. Too often they will assume that the solution is to add more lead so that they can stay down. That is the exact opposite of what you want to do. If you have enough lead to go down, you have enough lead, at least until your tank gets near empty. As EFX indicated, the problem is the expansion of air in the BCD when you ascended a bit. If you add more lead unnecessarily, then to get neutral you have to add more air to the BCD to compensate for it. For every pound you add, you have to add almost an additional pint of air to compensate. Now you have more air in the BCD to react to changes in depth and pull you to the surface. You have less capability to overcome all that extra air volume changes with your lungs, and you are even more at the mercy of your BCD than you were before. You have made the problem worse.

 

[EFX]

Having more weight than needed can throw your trim off unless you're unconsciously staying horizontal. Why is this? The lead is lower than the BC bladder so when you add air it tends to pivot your chest around the lead and you'll swim diagonally. Resistance of the water increases and you'll need more energy to swim and hence use more air. If your trim is good you'll use more air anyway because the BC has a bigger volume and hence more resistance to swim.

To reduce gas consumption: Get your weight right (no more than +2 lbs[1 kg] heavy). Get your trim right. Streamline equipment. Personal: stay fit, get enough sleep, eat right. Relax: Do proper dive planning. Get a good buddy you can trust. Dive within your training and experience to reduce anxiety. Have I left anything out?

 

[Tigerman]

I forgot I left my camera on the boat once while sitting in the zodiac.. 2kg of lead in a side pocket instead of the camerarig in your hands - now that'll mess with your trim