Old divers go without BC's,
freedivers go without tanks
nude divers go without wetsuits (nuda right?)
what next?
freedivers go without tanks
nude divers go without wetsuits (nuda right?)
what next?
Anyone dive without a BC?
- Thread starter ScottB
- Start date
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*Floater*
Contributor
ScottB:
This is your estimate right? Maybe you should test it out by taking a full breath of air and then blowing it into an SMB or a bag of some sort. Then see how much lead you need to sink the bag. I'd like to do the test myself, but don't have weights at home.
OP
ScottB
Contributor
Yes, it is an estimate, which I will explain below.. I have not measured my own vital lung capacity...
What I did is searched the web for average lung vital capacity.. came up with 4.2 Liters, Used a conversion chart to find out how many liters per cubic foot (28.317), and then worked out displacement based on 62.4 pounds per cubic foot of fresh water and 64 pounds per cubic foot for salt water..
(4.2l)/(28.317l/cuft)*62.4lb/cuft= +9.255 lbs buoyancy full inhale freshwater
(4.2l)/(28.317l/cuft)*64lb/cuft= +9.493 lbs buoyancy full inhale saltwater
Breathing using only the top half of vital capacity would average to 3/4 of the full buoyancy for +6.94 lbs freshwater, +7.12 lbs saltwater.
Breathing using only the bottom half of vital capacity would average to 1/4 of the full buoyancy for +2.313 lbs freshwater, +2.373 lbs saltwater.
If a person has comfort using these half ranges of tidal volume, then the difference between these average values values would constitute the the change in buoyancy of a tank that one *should* in theory be able to compensate for.
6.94-2.313~4.627 lbs change in freshwater buoyancy
7.12-2.373~4.747 lbs change in saltwater buoyancy
using 1.3 grams per liter as weight for air at STP, air is approximately .08116 lbs/cuft, so a change of 57.9 cuft results in a change of 4.7 pounds. So using a AL 63 and finishing with a reserve capacity of 5 cuft (238 psi) or using a Faber FX 72 (3442 psi) with an intial pressure of 3000 psi (overall less weight, and larger safety factor for filling =) results in an intial capacity of 62.8 cubic feet.. so finish with 5 cuft, 239 psi, and you have the same change in weight .. from a lighter, smaller cylinder with a larger safety margin on pressure when filling.. so you can get a hot fill and let it cool without violating the DOT maximum.. (though I know quite a few people often surpass this magic number
What I did is searched the web for average lung vital capacity.. came up with 4.2 Liters, Used a conversion chart to find out how many liters per cubic foot (28.317), and then worked out displacement based on 62.4 pounds per cubic foot of fresh water and 64 pounds per cubic foot for salt water..
(4.2l)/(28.317l/cuft)*62.4lb/cuft= +9.255 lbs buoyancy full inhale freshwater
(4.2l)/(28.317l/cuft)*64lb/cuft= +9.493 lbs buoyancy full inhale saltwater
Breathing using only the top half of vital capacity would average to 3/4 of the full buoyancy for +6.94 lbs freshwater, +7.12 lbs saltwater.
Breathing using only the bottom half of vital capacity would average to 1/4 of the full buoyancy for +2.313 lbs freshwater, +2.373 lbs saltwater.
If a person has comfort using these half ranges of tidal volume, then the difference between these average values values would constitute the the change in buoyancy of a tank that one *should* in theory be able to compensate for.
6.94-2.313~4.627 lbs change in freshwater buoyancy
7.12-2.373~4.747 lbs change in saltwater buoyancy
using 1.3 grams per liter as weight for air at STP, air is approximately .08116 lbs/cuft, so a change of 57.9 cuft results in a change of 4.7 pounds. So using a AL 63 and finishing with a reserve capacity of 5 cuft (238 psi) or using a Faber FX 72 (3442 psi) with an intial pressure of 3000 psi (overall less weight, and larger safety factor for filling =) results in an intial capacity of 62.8 cubic feet.. so finish with 5 cuft, 239 psi, and you have the same change in weight .. from a lighter, smaller cylinder with a larger safety margin on pressure when filling.. so you can get a hot fill and let it cool without violating the DOT maximum.. (though I know quite a few people often surpass this magic number
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yea, I have used a backpack before and I like it. Also, I prefer diving with my inflator disconected. This way, I can inflate my SMB more easiliy. Sometimes I wish I had it in downdrafts when my hands are busy with the camera. Inflating orally and using your lungs is much more precise.
OP
ScottB
Contributor
Oh.. and using a spring scale to pull the bag under water would probably be more accurate... no factoring in density of weights.. no having to make sure each weight weighs what it is stamped..
ChrisA
Contributor
I know someone who dives exactly as you describe. He started diving in the 1970's before there were BCs. Back then no one used BCs. He just never bought one. Yes he dives small tanks, like 72 cu ft but some one with 30+ years experiance can get good bottom times with little air.
The advantage of having no BC is that you are VERY streamlined so you use less effort to swim. With just a steel 72 and a reg you're not pushing much through the water.
You need to be a good swimmer to do this. On the surface with no BC you are only neutral, not 35 lbs positive like with a full blown up wing.
The advantage of having no BC is that you are VERY streamlined so you use less effort to swim. With just a steel 72 and a reg you're not pushing much through the water.
You need to be a good swimmer to do this. On the surface with no BC you are only neutral, not 35 lbs positive like with a full blown up wing.
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Dude... you're makin' this WAY more complicated than it needs to be. Strap your bp onto the tank, leave your wing in your bag and go diving.
OP
ScottB
Contributor
Taking Wikipedia.org with a grain of salt, but they say for an average 70kg (154lb) adult male:
Total lung capacity (TLC) = 6 L. The volume of gas contained in the lung at the end of maximal inspiration.
Vital capacity (VC) = 4.8 L. The amount of air that can be forced out of the lungs after a maximal inspiration.
Tidal volume (TV) = 500 mL. The amount of air breathed in or out during normal respiration.
So, if one is comfortable in adjusting within what portion of their Vital Capacity that they are utilizing for Tidal Volume, then the swing could actually be even more than the 4.7 pounds...... Rough math based on 4.2 l vital capacity and 1/2 l tidal volume has a change in buoyancy capability of just over 8 pounds..
Total lung capacity (TLC) = 6 L. The volume of gas contained in the lung at the end of maximal inspiration.
Vital capacity (VC) = 4.8 L. The amount of air that can be forced out of the lungs after a maximal inspiration.
Tidal volume (TV) = 500 mL. The amount of air breathed in or out during normal respiration.
So, if one is comfortable in adjusting within what portion of their Vital Capacity that they are utilizing for Tidal Volume, then the swing could actually be even more than the 4.7 pounds...... Rough math based on 4.2 l vital capacity and 1/2 l tidal volume has a change in buoyancy capability of just over 8 pounds..
OP
ScottB
Contributor
Stephen, I've already decided to do it.. Just waiting for my new toys to arrive and a roadtrip to warm waters to do it in
Mark Meadows low profile back plate, DSS Hogarthian harness, and the reg ive been saving up for.. Poseidon Xstream =)
Mark Meadows low profile back plate, DSS Hogarthian harness, and the reg ive been saving up for.. Poseidon Xstream =)
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Dang... you were too fast!
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