Hi and looking for tech expert to help wit a new product development

[OceanDesigner]

Hi,
I am not a diver but a designer of underwater apparatus. I'm looking for the right place to post a question regarding what it would take to raise a small, hollow object (like a plastic ball) from 1,000 ft. Any help would be greatly appreciated!

 

[tursiops]

Hi,
I am not a diver but a designer of underwater apparatus. I'm looking for the right place to post a question regarding what it would take to raise a small, hollow object (like a plastic ball) from 1,000 ft. Any help would be greatly appreciated!

I suspect "a small, hollow object (like a plastic ball)" at 1000 ft would be crushed, with no residual buoyancy. So bringing it to the surface means adding a small amount of buoyancy to offset its in-water weight.

Are you really asking the question to which you want the answer?

 

[boulderjohn]

You can ask it in Basic Scuba if you like, or maybe this is enough. Let me give you the basics right now. I am going to assume that your object at 1,000 feet is inflexible, like a hollow bowling ball. If it is flexible, like a balloon, it will be thoroughly crushed.

It comes down to two things: weight and volume. It does not matter if it is hollow, except for the degree to which its being hollow affects its weight. If it is inflexible, the depth does not matter, either. If it is flexible, the object will expand as it rises, so it makes a big difference.

You measure the volume, and you measure the weight. Then you compare those figures to the weight of that volume of water. If the object weighs less than that volume of water, it will rise to the surface. If it is more than that volume of water, it will sink.

In order to raise an object that is heavier than water, you attach something to it that is lighter than water, so that their combined weight and volume are less than water. This is typically done with a lift bag, which is essentially a balloon that you inflate until it has enough air volume to raise the object to the surface. The technique used depends upon whether you want it to rise in a controlled fashion or rocket out of control to the surface. If you put just enough air in a lift bag at 1,000 feet to get the object rising, the air in that bag will expand to about 31 times its size by the time it reaches the surface or else be so full it will be bursting as it ascends, so you will want to have a way to vent that expanding air.

 

[Andyoak]

Hi,
what it would take to raise a small, hollow object (like a plastic ball) from 1,000 ft. Any help would be greatly appreciated!

Positive buoyancy > negative buoyancy of the object.

Am I missing something?

 

[boulderjohn]

OK, I see from something you wrote elsewhere that you are looking for information on Boyle's Law. I therefore assume that your hollow object is flexible, and you want to be able to predict the degree to which it will expand as it rises.

The formula you are looking for is V1 X P1 = V2 X P2

That means that the volume you are starting with (V1) multiplied by the pressure it is under (P1) will equal its new volume (V2) multiplied by its new pressure (P2). The pressure is in atmospheres. Using basic algebra to solve the equation, you see that you find the new volume by dividing the left side of the equation by the new pressure.

To find the amount of atmospheres at a given depth of sea water, you divide by 33 and add 1 for the atmospheric pressure. To find the amount of atmospheres of fresh water, dive by 34 and add 1. (It is slightly more complicated at altitude.) At 1,000 feet in the ocean, the atmospheres of pressure are 1,000/33 + 1 = 31.3.

If you have a 1 liter balloon at 1,000 feet and will bring it to the surface (1 atmosphere) the equation is 1 X 31.3 = V2 X 1. That means your balloon will increase in volume 31.3 times when it gets to the surface.

 

[descent]

Welcome to ScubaBoard!

Don't worry about posting in the correct sub-forum. A thread starts out assigned to one particular category or another, but that can be changed by a moderator, if necessary. More than one "Ouch! Why does this hurt?" thread started in Basic-Scuba and was moved to Dive-Medicine after the diagnosis came back.

Different instrument payloads may require different strategies to get them back.

One common strategy is constant-volume: usually syntactic foam plus concrete or cast iron weights that can be released. Really heavy weights are difficult to deal with. They require deckhands in steel-toed boots to load, vast faith in your mathematical ability (electromagnetic or galvanic release) and cranes for launching.

Another is variable-volume. I personally do not like working around systems that include compressed gas and a flexible bladder because they sometimes inflate at the surface before launch. This is usually hilarious or startling, but the possibility always exists that someone could get hurt, as with an automobile airbag injury. The greater your target operating depth, the more dangerous your system becomes at the surface. Some gliders and motorized AUVs have rigid buoyancy tanks like a naval submarine that can be flooded and purged.

If you know a less-expensive way to drop and recover instruments reliably, your product will get a lot of attention. Ocean scientists are always budget-constrained.

Please do keep us updated, and best of luck!