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TomP:
:shakehead
That is just crazy.
Misconceptions and Fallacies
- Thread starter Charlie99
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:shakehead
That is just crazy.
OP
Charlie99
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Or maybe that's just what TomP heard when people were really telling him that his rig was too negatively buoyant, and that he should change gear (such as tank) so that he needed a bit of ditchable weight to be properly weighted.DivingCRNA::shakehead
That is just crazy.
Big difference.
TomP
Contributor
Charlie99:
Nope, the former. I chose my words fairly carefully in failed attempt to avoid this dialog. While you are technically correct, I am not too negative unless you think an unweighted diver should be a buoy. The observations i mentioned were made pre-dive on the boats and not as a post mortem on my trim or anything else.
Blackwood
Contributor
TomP:
Odd. "Add weight so that you can get rid of weight." That makes no sense. Adding weight when you are neutral means you have to add buoyancy. An emergency that requires you to ditch likely involves a loss of buoyancy, so you're back at square one.
Temple of Doom
Contributor
From what I gather, dumping a few pounds really only speeds your time to the surface slightly (while introducing many issues with speed of ascent, however I'm talking about cases where drowning is the less favourable outcome).
I imagine that in cases where dumping a few pounds would make a measurable difference on the outcome of the mishap (not drowning versus drowning), that a few gulps of air from another air source (spare-air or other such device) would also make that difference.
Having a secondary air source would probably have a measurable difference in cases where dropping a few pounds wouldn't.
I'd think that you're probably better off not thinking of a couple extra blocks of lead as a safety device.
Craig
I imagine that in cases where dumping a few pounds would make a measurable difference on the outcome of the mishap (not drowning versus drowning), that a few gulps of air from another air source (spare-air or other such device) would also make that difference.
Having a secondary air source would probably have a measurable difference in cases where dropping a few pounds wouldn't.
I'd think that you're probably better off not thinking of a couple extra blocks of lead as a safety device.
Craig
OP
Charlie99
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The advantage of having some ditchable weight isn't to speed up an ascent. IT has to do with staying on the surface with full tanks and buoyancy failure.
If a diver has no ditchable weight and is properly weighted, then if he has buoyancy failure at the beginning of a dive he will be negatively buoyant by the weight of the gas he is carrying. Having a gear config such that you have a few pounds of ditchable weight when properly weighted makes it possible to dump weight and be neutral or positive on the surface, even with full tanks.
If a diver has no ditchable weight and is properly weighted, then if he has buoyancy failure at the beginning of a dive he will be negatively buoyant by the weight of the gas he is carrying. Having a gear config such that you have a few pounds of ditchable weight when properly weighted makes it possible to dump weight and be neutral or positive on the surface, even with full tanks.
Tigerman
Contributor
Mass and weight
1. Mass is measured in kg and your mass is constant, regardless of wether youre on the moon, jupiter or earth.
2. Weight is measured in Newton and is a force, calculated by w = m*g where m is mass and g is gravitational pull.
My mass is ~80kg, which would make my weight 784 newton.
3. The scale show your weight because it is the negative force that keep you from freefalling and it measures the ammount of force it use to keep you from falling.
4. Weightlessness is a state of being in free fall with no percieved support (such as the floor). Which means you are weightless if youre in the elevator and the cable breaks, the rollercoaster goes over the top of the hill and so on..
The question is only if the lift from your gear would be considered "support".
1. Mass is measured in kg and your mass is constant, regardless of wether youre on the moon, jupiter or earth.
2. Weight is measured in Newton and is a force, calculated by w = m*g where m is mass and g is gravitational pull.
My mass is ~80kg, which would make my weight 784 newton.
3. The scale show your weight because it is the negative force that keep you from freefalling and it measures the ammount of force it use to keep you from falling.
4. Weightlessness is a state of being in free fall with no percieved support (such as the floor). Which means you are weightless if youre in the elevator and the cable breaks, the rollercoaster goes over the top of the hill and so on..
The question is only if the lift from your gear would be considered "support".
TomP
Contributor
Charlie99:
As does a redundant buoyancy capability.
I can't believe that after reading through 23 pages of this, no-one has mentioned the number one diving myth...
Once you've bought all you own kit, you don't need to buy anything else and diving is cheap!
Dom
Once you've bought all you own kit, you don't need to buy anything else and diving is cheap!
Dom
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