We were given a single photograph and some words to help us identify this item. While it appears that the poster is holding it with only one finger, the text tells us that it is four or five pounds in weight. Not what a typical float would weigh. Many of the modern floats are made from a hard syrofoam material and weigh practically nothing.

If we called something a 'bouey' that means it has boyancy and will float. Using the word 'float' would also indicate that it can float.

The fact that a thing/item can be somewhat buoyant, meaning that while it may not float on the surface by also will not sink to the bottom of the ocean makes sense that this unknown item can be a weight to control the net under the water.

Looks like @RickCorey got it right back in post #920046 when he said... "a rope could thread through those holes". But it wouldn't float, so it isn't to hold a net up. Maybe weights for the bottom of a net, to hold it down?

Good to know that the unknown item has now been identified.

Perhaps someone could weigh it?

http://www.tidalropes.com/traw... Please note these are for middle & high depths

http://www.nichimo-marine.jp/p... Note the chart lists depth, weight & bouyancy figures

Never the less, these are "termed" floats by the trawler industry. They are floats because the DO float at SOME depth. Not all nets have floats on the top line that FLOAT ABOVE the water. It depends on what level the fish are. One might want the net to begin at 30' depth and end at 60' depth. I would suspect that the "ears" are for very quick connect attachment rigs to the net so they can be easily changed to change the depths the net is to drag.

FYI, one of the definitions of trawl
a large wide-mouthed fishing net dragged by a vessel along the bottom or in the midwater of the sea or a lake. NOTE it states bottom or midwater

There are a number of similar looking metal objects on a Google search using the keywords metal mooring net fishing float:

https://www.google.ca/search?q...

or buoy

https://www.google.ca/search?q...

I agree that this thing is a fishing net float of some sort, but none of the ones pictured have the cavity. This one is special. What is it for?

Wow wow wow

I don't have access to a pool but will next week
I have to say, I have been going through some pretty tough stuff the last two weeks and this is very entertaining
And I appreciate it

I sent an email to one of the companies that sell floats/weights, etc. I hope they give us an answer. I provided a link so they can read the thread, see the photos and read our many answers.

Still searching...
A long time ago, in addition to rocks/stones, the Conch shell was used to weigh down the nets. If you think of the shape of the Conch shell, which is hollow-ish, yes it would certain keep a net from floating. I saw some references to fish net weights called 'Dog Conch' but my patience wore thin looking at results with actual dogs and dog toys, not fishing-related responses. Maybe someone else will have more luck looking for the man-made version of the Dog Conch fish net weight.

Here is a quote from this link:
http://datab.us/i/Fishing%20ne...
"Despite their ornamental value, dog conches are traditionally used by local fishermen as sinkers for their fishing nets."

Jolana said:Wow wow wow

I don't have access to a pool but will next week
I have to say, I have been going through some pretty tough stuff the last two weeks and this is very entertaining
And I appreciate it

Now I'm going to rescind my statement about the pool. Reason being that these floats are designed to float at a certain depth. We don't know what depth yours is designed to float at so tossing it in a pool will not tell us anything UNLESS it floats on top of the water. Then we know it floats on top of the water. But if it sinks, it does not mean it doesn't float at a certain depth in the ocean -- 30, 40, 50 or 80 feet deep which a pool does not achieve. Furthermore salinity of the water has a great deal to do with the degree to which things float and a pool is not salt unless you're going to a salt water pool of course. So throwing it in a pool will only test if it floats on top period.

I was trying to imagine how a float could "select" a certain depth and pull part of a net down or up to that depth.

Since water is almost completely incompressible (*), I couldn't think of ways an object could have different buoyancy at different depths, other than these two, so I thought "trawler floats can't be depth-specific!"

1. the float compresses under pressure (same mass, smaller displacement volume). That would cause it to have less buoyant force at greater depths.

However, if a net dragged such a float down a little, the buoyant force would become less and the net would tend even more strongly to fall.

To be depth-specific, a float would have to become MORE buoyant as it went deeper, so that the weight pulling it down would eventually reach an equilibrium.

2. the float's density is exactly equal to seawater, so there is a TINY lifting or sinking force moving it to find the precise salinity and temperature to match the density of the float.

But the force is tiny: only the float's volume times the difference in density between seawater at different depths, and water is almost totally incompressible, so the density change is TINY.

Then I found a book that seemed to agree with me.

https://books.google.com/books...

It said in part:


I was content with that answer until I started to think about it.
But I came back to thinking the same thing, so you can skip this following digression with no loss!

Maybe the "hollow" would make the floats select a certain depth and float or sink with significant force to reach that depth, if the air can't escape from the hollow.

Hmmm.

Imagine a bucket held carefully upside-down so air can't escape. It floats at the surface since a lot of air and a little sheet metal are much lighter than an equal volume of water.

Now add bricks until the bucket just starts to sink.

It will sink until water pressure compresses the air and lets some water into the hollow space. You can say this either way:

1. the mass of the bucket-shaped-volume increased a lot, by the mass of the water entering it. The volume "stayed the same" because we are counting the entire volume of the bucket-shaped cubic, whether it is filled with water or air.

2. the volume of the AIR-FILLED part of the bucket just dropped greatly while the mass stayed the same. (In #2, we no longer count the volume filled with water as p[art of the "bucket").

The volume is less, so the bucket displaces less water, so the buoyant force is less.

However, this case (no matter which way you look at it) is just like the case where "the float compresses under pressure". As soon as you give it enough weight that it starts to sink, its buoyancy decreases with depth and it sinks faster and deeper.

If I'm right, you could add bricks and pebbles until the bucket JUST had neutral buoyancy as it floated JUST below the surface of the water. Now add one small grain of sand. Now it's heavier and sinks an inch. That compresses the air a little, buoyancy decreases a little, and the bucket is heavier and sinks faster. More compression, less buoyancy, faster sinking.

Promptly the bucket falls to the bottom of the pool and hits with a CLUNK.
That would not have held any part of a net at any specific depth.

As a check, imagine a very strong plastic bag, sealed tight and unburstable, floating at the surface. Add bricks until it just starts to sink. It will sink faster and faster as it compresses.

Now I'm back to thinking that I don't understand any way a float could be depth-specific.

Increased pressure compressing air "goes the wrong way": it creates positive feedback which makes a bucket go "clunk" to the bottom or float stubbornly on the surface.

If water were highly compressible (like gasses are), any rigid object would float to the depth where pressure compressed the fluid to the exact density of the rigid object. But, the force the object could exert on the net (sinking or buoyant force) is only the object's volume times the difference in density between the object and whatever level the net dragged it to (away from its neutral-buoyancy-depth)

Anyway, that's the way it looks to me right now. I could be wrong: I changed my mind twice while trying to figure this out.

(*)
Allegedly, at one mile of depth in seawater, the pressure is around 150 times atmospheric, but water only compresses 1%!

If that's linear, at 530 feet water only compresses 0.1%.
At 53 feet, 0.01%. (0.01% is like a factor of 0.0001)

A gallon of water weighs 8.34 pounds ("a pint's a pound the world 'round").

So the density difference from the surface to 53 feet of depth would make one gallon weigh 0.00834 pounds = 0.13 ounces = 4 grams more.

I don't think 4 grams per gallon of float volume (translated into force) would drag a very big net up or down very far.

OMG, Rick -- I believe you have outdone yourself this time!

(I pretty much have no idea what you said there... )

Physics is NOT my expertise, so I'm hoping someone will agree or disagree.

But if you have a small bucket and a swimming pool, you might be able to demonstrate what happens in the confusing case.

I think that as soon as it STARTS to sink, it will sink faster and faster.
It won't seek out a depth at which something balances something else (I think).

But how many deep-sea fishermen who use nets hang out in ATP?

Any recent phyzzies majors?

RickCorey said:I was trying to imagine how a float could "select" a certain depth and pull part of a net down or up to that depth.

Since water is almost completely incompressible (*), I couldn't think of ways an object could have different buoyancy at different depths, other than these two, so I thought "trawler floats can't be depth-specific!"

1. the float compresses under pressure (same mass, smaller displacement volume). That would cause it to have less buoyant force at greater depths.

However, if a net dragged such a float down a little, the buoyant force would become less and the net would tend even more strongly to fall.

To be depth-specific, a float would have to become MORE buoyant as it went deeper, so that the weight pulling it down would eventually reach an equilibrium.

2. the float's density is exactly equal to seawater, so there is a TINY lifting or sinking force moving it to find the precise salinity and temperature to match the density of the float.

But the force is tiny: only the float's volume times the difference in density between seawater at different depths, and water is almost totally incompressible, so the density change is TINY.

Then I found a book that seemed to agree with me.

https://books.google.com/books...

It said in part:


I was content with that answer until I started to think about it.
But I came back to thinking the same thing, so you can skip this following digression with no loss!

Maybe the "hollow" would make the floats select a certain depth and float or sink with significant force to reach that depth, if the air can't escape from the hollow.

Hmmm.

Imagine a bucket held carefully upside-down so air can't escape. It floats at the surface since a lot of air and a little sheet metal are much lighter than an equal volume of water.

Now add bricks until the bucket just starts to sink.

It will sink until water pressure compresses the air and lets some water into the hollow space. You can say this either way:

1. the mass of the bucket-shaped-volume increased a lot, by the mass of the water entering it. The volume "stayed the same" because we are counting the entire volume of the bucket-shaped cubic, whether it is filled with water or air.

2. the volume of the AIR-FILLED part of the bucket just dropped greatly while the mass stayed the same. (In #2, we no longer count the volume filled with water as p[art of the "bucket").

The volume is less, so the bucket displaces less water, so the buoyant force is less.

However, this case (no matter which way you look at it) is just like the case where "the float compresses under pressure". As soon as you give it enough weight that it starts to sink, its buoyancy decreases with depth and it sinks faster and deeper.

If I'm right, you could add bricks and pebbles until the bucket JUST had neutral buoyancy as it floated JUST below the surface of the water. Now add one small grain of sand. Now it's heavier and sinks an inch. That compresses the air a little, buoyancy decreases a little, and the bucket is heavier and sinks faster. More compression, less buoyancy, faster sinking.

Promptly the bucket falls to the bottom of the pool and hits with a CLUNK.
That would not have held any part of a net at any specific depth.

As a check, imagine a very strong plastic bag, sealed tight and unburstable, floating at the surface. Add bricks until it just starts to sink. It will sink faster and faster as it compresses.

Now I'm back to thinking that I don't understand any way a float could be depth-specific.

Increased pressure compressing air "goes the wrong way": it creates positive feedback which makes a bucket go "clunk" to the bottom or float stubbornly on the surface.

If water were highly compressible (like gasses are), any rigid object would float to the depth where pressure compressed the fluid to the exact density of the rigid object. But, the force the object could exert on the net (sinking or buoyant force) is only the object's volume times the difference in density between the object and whatever level the net dragged it to (away from its neutral-buoyancy-depth)

Anyway, that's the way it looks to me right now. I could be wrong: I changed my mind twice while trying to figure this out.

(*)
Allegedly, at one mile of depth in seawater, the pressure is around 150 times atmospheric, but water only compresses 1%!

If that's linear, at 530 feet water only compresses 0.1%.
At 53 feet, 0.01%. (0.01% is like a factor of 0.0001)

A gallon of water weighs 8.34 pounds ("a pint's a pound the world 'round").

So the density difference from the surface to 53 feet of depth would make one gallon weigh 0.00834 pounds = 0.13 ounces = 4 grams more.

I don't think 4 grams per gallon of float volume (translated into force) would drag a very big net up or down very far.

But what about the sanity, er um salinity, um or insanity?

Somehow I don't think there is a great deal of physics involved in professional fishing. Around here they can't even figure out how to catch fish without turtles being snared. I doubt there is much concern for specific gravity as related to salinity and depth.

Back to the arboreal witches! No one else has a use for that hollow in the top. (Or bottom, depending on how it decides to float/sink.)

>> But what about the sanity, er um salinity, um or insanity?

I never thought about that, but maybe sanity does find its own level.

I'll try not to drag too many people down with me!

You know I just had to throw that out there Rick. It was too good an opportunity to pass up.

RickCorey said:>> But what about the sanity, er um salinity, um or insanity?

I never thought about that, but maybe sanity does find its own level.

I'll try not to drag too many people down with me!

Too late for me!

Insanity, salinity.
I copied Rick's post plan to read it when we have a rainy day. Good stuff but it will take me hours to read and understand all of it.

Someone mentioned witches. I collect some of the glass floats as seen in this link:
http://www.bonanza.com/items/l...

I like the blue or green ones the best. They are sometimes called 'witches balls'...(golly, somehow that looks wrong, sorry ) but these glass balls can definitely float.

"They are sometimes called 'witches balls'...(golly, somehow that looks wrong, sorry "

It seems that humor along with water seeks its' lowest level...

thank goodness for that