sciencegeek
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Could you tell me how to determine how much weight is needed to cause a person to sink? Is it a mathmatical equation that is used or does it just depend on the person? Thanks for your help!
Determining Weight
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The amount of weight you need depends on a few things:
1. Your gear. Some gear is more negatively buoyant; therefore, you don't need as much on your belt.
2. Your physical shape. Muscle sinks, fat floats.
3. Your natural characteristics. Some people are corks, others are rocks.
4. Your experience level. Newbies do little things that actually generate lift. More experienced people do these only when they want to rise.
For the most part there are a couple "rules of thumb" for determining a starting point for weight (instead of a random guess), but in the end nothing beats a proper weight check.
1. Your gear. Some gear is more negatively buoyant; therefore, you don't need as much on your belt.
2. Your physical shape. Muscle sinks, fat floats.
3. Your natural characteristics. Some people are corks, others are rocks.
4. Your experience level. Newbies do little things that actually generate lift. More experienced people do these only when they want to rise.
For the most part there are a couple "rules of thumb" for determining a starting point for weight (instead of a random guess), but in the end nothing beats a proper weight check.
Ontario Diver
Guest
No - there is no mathematical equation.
There are factors such as body weight, salt or fresh water, ratio of light tissues (like fat) to heavy tissues (like bone), exposure suits, gear, and most importantly your comfort in the water.
You should have been given some basic guidelines in your open water course and spent some time in the pool and in the open water getting it set up right.
Your weighting will change as you dive more and more, getting lighter as you become more comforable in the water.
There are rules of thumb but at the end it will turn into trial and error.
There are factors such as body weight, salt or fresh water, ratio of light tissues (like fat) to heavy tissues (like bone), exposure suits, gear, and most importantly your comfort in the water.
You should have been given some basic guidelines in your open water course and spent some time in the pool and in the open water getting it set up right.
Your weighting will change as you dive more and more, getting lighter as you become more comforable in the water.
There are rules of thumb but at the end it will turn into trial and error.
What DBailey said is correct.
Now about formulas, in general terms as a place to start from, weigh your wet suit. If it is a 7mm take 3 lbs lead x weight of wet suit. Then figure your fat, usally done by deducting your weight in High School From today and add 10% of that difference pluse 4 lbs if diving an AL80 tank. If you are diving a 3 mil wetsuit, the calculations are the same except you use 1 lbs lead x weight of wet suit.
The above you get you into the neighborhood and most likely a tad heavy. But once in the water you need to do a weight check which is the only true way to get your weights right.
Now about formulas, in general terms as a place to start from, weigh your wet suit. If it is a 7mm take 3 lbs lead x weight of wet suit. Then figure your fat, usally done by deducting your weight in High School From today and add 10% of that difference pluse 4 lbs if diving an AL80 tank. If you are diving a 3 mil wetsuit, the calculations are the same except you use 1 lbs lead x weight of wet suit.
The above you get you into the neighborhood and most likely a tad heavy. But once in the water you need to do a weight check which is the only true way to get your weights right.
mccabejc
Contributor
Here's my shot a a formula.
Formula good. Me like formula.
In general, a men's neoprene jumpsuit has two to three pounds of buoyancy at the surface for each millimeter of thickness. Therefore, a 7mm wetsuit has about +14 to +21 lbs of buoyancy.
Regulators and the instruments are generally -1 to -2 lbs.
Your BC is nearly neutral.
The buoyancy of a standard aluminum 80-cubic-foot cylinder, with 3000 psi in salt water is -2.5 pounds. Breathe it down from 3,000 psi to 500 psi, and it's about +2.5 pounds. Now you are five pounds more buoyant. Here's the link to a chart showing buoyancy of various cylinders at various psi's in salt/fresh water.
http://www.deep-six.com/page66.htm
Ipso facto, the net gear buoyancy with a full AL80 tank in salt water is about this:
Suit: +14 to +21
Reg: -1 to -2
Tank: -2.5
So your gear is somewhere between 10 and 18 lbs buoyant in salt water with a full tank. With a tank at 500psi, you are now between 15 and 23 lbs buoyant.
Formula good. Me like formula.
In general, a men's neoprene jumpsuit has two to three pounds of buoyancy at the surface for each millimeter of thickness. Therefore, a 7mm wetsuit has about +14 to +21 lbs of buoyancy.
Regulators and the instruments are generally -1 to -2 lbs.
Your BC is nearly neutral.
The buoyancy of a standard aluminum 80-cubic-foot cylinder, with 3000 psi in salt water is -2.5 pounds. Breathe it down from 3,000 psi to 500 psi, and it's about +2.5 pounds. Now you are five pounds more buoyant. Here's the link to a chart showing buoyancy of various cylinders at various psi's in salt/fresh water.
http://www.deep-six.com/page66.htm
Ipso facto, the net gear buoyancy with a full AL80 tank in salt water is about this:
Suit: +14 to +21
Reg: -1 to -2
Tank: -2.5
So your gear is somewhere between 10 and 18 lbs buoyant in salt water with a full tank. With a tank at 500psi, you are now between 15 and 23 lbs buoyant.
donacheson
Contributor
sciencegeek:
If you're scuba diving, you want just enough weight so you can be neutral just below the surface with an empty BC and a near-empty tank and breathing normally. Then you'll always be able to be neutral at any point during the dive and fully control your ascent at the end of a dive.
Naked??? Not very much. Humans are close to being neutral, with some more and some less. Most need a pound and a few need a bit more to sink in their bathing suits. This does not take into account any hyperventilation which will increase the amount of weight needed to sink.
The real problem lies in what we are wearing. Fat people wear far more neoprene for warmth and that is very, very bouyant.
The real problem lies in what we are wearing. Fat people wear far more neoprene for warmth and that is very, very bouyant.
sciencegeek:
It depends on a couple of factors. Body composition is one with adipose tissue being more bouyant than denser bone and muscle tissue.
Also how much air is in the persons lungs makes a difference. We had a slender teenage boy get hit by a jet ski and sink very quickly as the impact essentially deflated his lungs.
mccabejc
Contributor
But considering a person alone (no gear), it seems to me that what NetDoc said is right on the mark: most people are pretty much neutral, since we are mostly water, no? So I'm thinking that the buoyancy of a person, nekkid as a jaybird, is pretty much neutral, and the inflation of your lungs can vary that by 4-6 pounds (I think I read that somewhere). So with lungs totally deflated you'd be pretty neutral.
Tell you what, it's almost 90 outside right now, and I'm sweating, and my swimming pool is lookin pretty good. I feel the need to perform a series of experiments !!!
Be right back.....
Tell you what, it's almost 90 outside right now, and I'm sweating, and my swimming pool is lookin pretty good. I feel the need to perform a series of experiments !!!
Be right back.....
donacheson
Contributor
mccabejc:
About twice that much - 8 to 12 pounds - isn't unusual. Hospitals and some doctors use a simple device, called a spirometer, to measure lung capacity, usually in liters. Roughly speaking, a liter is two pints and a pint of air displaces about a pound of water.
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