Water as weight rather than lead?

[DA Aquamaster]

I believe very small rocks also float.

K

Monty Python movies aside, rocks are about 3.0 to 3.5 times as dense as water but very small rocks will still remain on the surface due to surface tension. So Monty is, after all is said and done, right.

What really confuses things is that submarines take on water in order to become less bouyant and therefore "dive". You could always wear doubles but keep one tank full of water instead of air. Really, if water caused negative bouyancy, we would all have light weight collapsible plastic weight bags we would add water to once we reached a dive destination or they would be built into our BC's.

BC's (or wings for the technically inclined diver) function just like ballast tanks where air is used to displace water and create bouyancy.

Now, some ROV's are also being designed with an electrically actuated piston to add or reduce space for water in a ballast tank to enable bouyancy changes to be made without having to rely on limited air supplies.

So you could cut the bottom out of your old AL 80 when it develops fatigue cracks, insert a suitable piston and actuator and develop an entirely new airless ballast system for scuba divers.

 

[Firefyter]

the question:

can you use water as weight, instead of lead weight?

For example, say that you take containers of water instead of lead. Yes, water weights six pounds per gallon, so you would have to take two gallons of water to equal 12 pounds, but...

Say you tie two milk gallons full of water to your waist...

Wouldn’t it be the same as wearing lead weights?

We were having this discussion, and someone was saying that wouldn’t work, because the water would “float on water."

is this correct?

Actually, fresh water weighs 8.338 lbs. per gallon, instead of six, and the reference in one of the earlier posts is right. Assuming you're in fresh water, and using fresh water in the jugs, the specific gravity of the water surrounding you and the water in the jugs is the same, which is 1. The only thing that would make it more or less bouyant is the container that you are using.

 

[H2Andy]

ok... sounds like our mystery diver was right...

thank you all; it's been very educational

 

[Afraid_of_Fish]

I love the sarcasm in here. You guys are hilarious.

 

[TwoTanks]

Monty Python movies aside, rocks are about 3.0 to 3.5 times as dense as water but very small rocks will still remain on the surface due to surface tension. So Monty is, after all is said and done, right.

If Monty Python is right, and witches float, then how many jugs of salt water does it take for two witches and a duck to dive in fresh water. Assuming the jugs are neutral, the duck has an aluminium 63 and its not a full moon.

 

[Diver0001]

the question:

can you use water as weight, instead of lead weight?

For example, say that you take containers of water instead of lead. Yes, water weights six pounds per gallon, so you would have to take two gallons of water to equal 12 pounds, but...

Say you tie two milk gallons full of water to your waist...

Wouldn’t it be the same as wearing lead weights?

We were having this discussion, and someone was saying that wouldn’t work, because the water would “float on water."

is this correct?

There are two ways of creating buoyancy (positive or negative). You can change the volume of a flexible object (which is how a BCD works) or you can change the mass of a fixed sized object (which is how a submarine works).

In the case that you wanted to make a diver work like a submarine then you would need to create a rigid trim-vest with in itself enough negative buoyancy to sink the diver (approximating a sub) when flooded. Adding air and/or water to the trim-vest would then change the diver's mass and he would sink or float.

In theory.

It would also be interesting to see if such a thing would be more stable than conventional BCD because of the weight distribution.....

R..

 

[Diver0001]

If Monty Python is right, and witches float, then how many jugs of salt water does it take for two witches and a duck to dive in fresh water. Assuming the jugs are neutral, the duck has an aluminium 63 and its not a full moon.

We need more information:

- Is the witch blonde or brunette?
- Is the duck diving Nitrox or air?
- Is it spring or fall...?

R..

 

[Charlie99]

In the case that you wanted to make a diver work like a submarine then you would need to create a rigid trim-vest with in itself enough negative buoyancy to sink the diver (approximating a sub) when flooded. Adding air and/or water to the trim-vest would then change the diver's mass and he would sink or float.

It would also be interesting to see if such a thing would be more stable than conventional BCD because of the weight distribution.....

It would have the advantage of not changing buoyancy with depth, as does the air bubble in a flexible BCD bladder.

When partially filled with water, it would tend to hold you in your current attitude, since the water would run to the low side, air bubble to the high side. Of course, normal BCs and wings do this too when partially inflated as the air bubble shifts to the high end (pitch trim) and to the high side (roll trim).

 

[Seabear70]

We need more information:

- Is the witch blonde or brunette?
- Is the duck diving Nitrox or air?
- Is it spring or fall...?

R..

RedHead

Tri-Mix

Summer

 

[yknot]

Yes. They switch between air to become pos to water to become neg.

Just like a divers bc. We fill the space with air or remove the air causing the same space to be occupied with water.

Not exactly-subs never really change their bouyancy, just their weight. Divers alter their bouyancy by changing their volume or displacement but not their weight, except for the decreasing weight of their air supply. Almost opposite actions to acheive the same results.