Testing Buoyancy At Depth

[StringJunky]

This is a question related to fishing with baits that are buoyant and anchored down by a weight off the bottom of a lakebed like in the image below:

 

 

When the water pressure gets too high the hook and popup lie flat on the deck. I'd like to see what happens to my popups in 15ft of water and see if they are still popped up and if not I will have to research popup media that work at that depth. One idea I had was to get a 16ft length of 6inch or so wide pipe with a clear container sealed on the bottom of it. This apparatus would be supported upright and then filled with water. I would then lower the rig to the bottom of this and see in the clear container if it still stayed popped up. My question is: Would the pressure at the bottom be directly equivalent to that of the same depth in a lake or would it be different?

 

Any other ideas for doing this test would be appreciated as well.

 

 

 

 

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Edited September 10, 2013 by StringJunky

[Externet]

Yes, the pressure at the bottom of a 16 ft. filled pipe will be the same as at 16 ft under the lake surface.

 

But the 'float' will not change its floating force if it is not compressible, as a ping pong ball. If it is a piece of meat that floats at the surface, it will stop floating and sink from a certain depth down.

[doG]

You can get a 1 foot piece of pipe with caps for both ends and use air pressure to simulate the depth of any size water column. For 16 feet use about 6.5 psi of air pressure.

[StringJunky]

You can get a 1 foot piece of pipe with caps for both ends and use air pressure to simulate the depth of any size water column. For 16 feet use about 6.5 psi of air pressure.

Will the popup rig stand upright under pressure equivalent to say 1 foot depth? This is a new one for me. Or do you mean there still needs to be some water in the lower half, assuming the pipe is upright?

[doG]

Will the popup rig stand upright under pressure equivalent to say 1 foot depth? This is a new one for me. Or do you mean there still needs to be some water in the lower half, assuming the pipe is upright?

You don't have to actually use a 16 foot column of water to simulate the equivalent pressure you would have at the bottom of the column. One foot of water with 6.5 pounds of additional air pressure (the weight of a 15 foot column of water) on top of it would simulate a pressure at the bottom the same as a 16 foot column of water.

[StringJunky]

You don't have to actually use a 16 foot column of water to simulate the equivalent pressure you would have at the bottom of the column. One foot of water with 6.5 pounds of additional air pressure (the weight of a 15 foot column of water) on top of it would simulate a pressure at the bottom the same as a 16 foot column of water.

Yes, my original apparatus was somewhat cumbersome but I was thinking economics and keeping it down. I'm thinking on the lines of a foot pump with a pressure gauge attached to something like you mention that has a car-type tyre valve fixed to it. I have access to a compressor as well.

[Enthalpy]

Adding some extra weight the buoy will sink. You could go with a boat to a place as deep as your target location, sink there the buoy+weight with a line, and measure the weight-minus-buoyancy with a dynamometer as the composite sinks. This will tell you by how much the buoyancy drops, and thus if the buoy is good enough to keep the hook as desired.