Water as weight rather than lead?

[LeFlaneur]

Platinum would be more effective, as would osmium.

I use uranium as weight so I don't have to carry a glow stick whilst night diving.

 

[The Kraken]

Yknot,
How does a sub change its weight, throw out some of the sailors.
If my memory serves me correctly, keep in mind I am getting old, the sub has ballast tanks. It is designed so that when the tanks are flooded the intrinsic weight of the submarine causes it to sink. However, when the ballast tanks are "blown" , and I hope that is the correct term, the water in the ballast tanks is forced out by compressed air, the ballast tanks become filled with air and result in a positively buoyant condition.

Weight and buoyancy are indirectly proportional with respect to displacement.

 

[The Kraken]

I guess you are correct, however, in the fact that the water displaced by the compressed air weighs more therefore the submarine weighs less, given that the water displaced is held internally in the ballast tanks.

The difference between the BC and sub is that that water that displaces the compressed air of the BC is external.

 

[TwoTanks]

We need more information:

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

R..

OK here is all the info I have....

1. The witches are red heads (we all know red heads are evil.. or at least misunderstood).
2. Ducks are very suceptable to narcosis so all ducks breath heliox for safety when diving.
3. It is summer time, however the dive takes place in a lake at MACHU PICHU in the southern hemisphere where it is now winter.
4. MACHU PICHU is 9060' above sea level
5. The water temp is 71f
6. The duck is diving comando, the first witch is in a mares semi-dry and the second witch is in a henderson 7/5mm hyperstretch suit.
7. Mercury is in retrograde
8. vis is about 20 feet
9. Witches don't like Salem Mass.
10. water freezes at 32f
11. A ducks quack doesn't echo, the mythbusters guys were wrong.
12. The earth rotates counterclockwise.
13. is an unlucky number
14. The volume of the caspian sea is 88 million cubic meters.
15. The chicken came before the egg
16. There are no left handed birds

If you need additional info, please use an almanac or search on line.

Thanks,

TT

By the way the answer is:

1 jug of indeterminate size each.

 

[Don Burke]

I guess you are correct, however, in the fact that the water displaced by the compressed air weighs more therefore the submarine weighs less, given that the water displaced is held internally in the ballast tanks.

The difference between the BC and sub is that that water that displaces the compressed air of the BC is external.

A modern submarine has internal trim tanks and external main ballast tanks.

When the main ballast tanks are vented, you can look at it as either decreasing displacement or increasing weight. The math ends up in the same place.

The plan is for the MBTs to be completely flooded when submerged so that the Diving Officer of the Watch does not have to chase a negative coefficient of buoyancy. Vents are normally cycled once a day to ensure there is no air in the tanks.

On the surface, the MBTs are pretty much full of air. Low pressure blows are done to try to keep them that way.

The internal trim tanks are either open to ship's atmosphere or slightly pressurized to hold prime on the trim pump. I have worked with both systems.

You still have the problem of free surface area in the internal tanks, but at least you are not fighting a compressing bubble.

 

[Hank49]

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?

To be negatively buoyant an object must displace a volume of water that weighs less than it does. Water will displace the same weight as itself so it will be more or less neutral. good for diving, not for sinking. The lead displaces a much less voume of water than it weighs...so it sinks. Didn't we learn this in our open water course?

 

[CathyI8205]

You guys need a life!

 

[glbirch]

Platinum would be more effective, as would osmium.

Mercury would be more comfortable. Depleted Urananium would be better for density and as an added bonus you won't need a flashlight anymore after you've used it for a while. Overall though, the head of an old politician might work best. Most dense thing I can think of.

 

[The Kraken]

I've often thought of depleted uranium for weights. I've dealt with that stuff and GEEEEZ is it heavy (dense). The problem is cutting the stuff. There really isn't a radioactivity problem, hence "depleted". A couple of pieces about the size of 2 "D" cell batteries would give you about 10 pounds of weight.

Depleted uranium has about twice the density of lead.

 

[beachbum70635]

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..

And what happens if you change the volume of the flexible object with water instead of air?