Water Pressure vs. Floatation

Any better?

What would be the name of this type of net?

Looks like less lift with the open mesh to me. They are acting essentially like a wing.

Running at the same speed, the closed mesh will rise more toward the horizontal plane, the open mesh will bow/curve more.

Somebody may come along with a formula, but, that isn't me.

The one thing that hits me immediately is the width (dimension in the direction of flow) of the ballast. As the angle of the net rises from the vertical, the current hits the top of the ballast in the net with the mesh but less so in the other because it is more shielded by the net. It could be significant if the net moves significantly off the vertical. The weight per unit of area is significant, too.

This, of course, is going much further than you asked. If you consider the current places a linear force along each of the horizontal strands, there must be more total horizontal fore on the net with most horizontal strands so that one will drag more than the one with the bottom of the net replaced by the grid.

One for and one against.

Hmm?

Lets wait and see who else chimes in.

My premise all these yeasr was still that the larger mesh allowed some water to pass through easier, thus allowing more of the fine mesh to lay over at a more controlled curve or belly.

The larger mesh lays more parrallel to the ballast?

where as the piece with the entire fine mesh, just bellies over quicker and forces the floatation down deeper in the water.

Thank you all so far for the input.

Here is a mini-version of it with a Border Rope sewn in and upside down.

Seems like there would be a lot more crap from the bottom in the net design without the high flow wide mesh at the bottom.

More muck, plants, shoes, rocks from the bottom would have to slow the rate the net could be pulled through the water and slow the rate with which the net could be cycled (having to remove all the non-fish items from the net). It also seems like having the wide mesh section could increase the longevity of the nets for similar reasons.

There's enough tech talk in here to spin anybody's head, the software programs mentioned could possibly provide the proof you need, or possibly even tweak your design.....

http://cdn.intechopen.com/pdfs/5395/InTech-Simulation_of_net_structures_hydrodynamic_fields.pdf

Thank you for the information. I may not be able to understand it but a look-n-see can not hurt my cause.

thank you.

My GUESS is that the one with the open weave section will produce less drag etc based on the following interpretation.

Both nets have the same free standing area, but 1/17th of the cross section is the open weave. This not only reduces the friction of the total net surface area but also provides a third "edge" for the water in the pressure zone in front of the more dense netting to escape to the rear of the net. I even suspect that this configuration would also develop a concave shape lower in the water (closer to the bottom weave) than the uniform net where the concave would expect to be dead centre. (Assumed the net is being drawn through the water.)

If the nets are free hanging and not being trawled, then the relative flexibility of the open weave would allow the upper portion of the net to "flop about" with lower direct connection to the bottom. (Assumed net weave is diamond style without direct vertical grid as shown in the schematic.) The diamond shapes are able to stretch and sag in the vertical axis more easily.

If it were me I'd tell whoever asked you to qualify your premise to %^&* off.
It's called experience and experimentation. The actual technical analysis would prob be glorified guess work based on a load of assumptions and fiddle factors adjusted to suit the real world results.

For pities sake when will these idiots realise that maths is an attempt to describe the real world not the other way round.

I'm sure many of us could create convincing sounding bull arguments for either configuration being 'better'

Grrrr ftzzzz hiss.
I can imagine stone age man having made the first bow and arrow being confronted by some idiot in a Mammoth skin suit asking for a technical justification.

Del

If you want to smack 'em in the mouth, you can say Del told you to do it

All you should need to be qualifying is how well it catches fish! Isn't that the idea.

Anytime lower the mesh size you decrease the surface area of the weave. A decrease in surface area a decrease in friction in this case to the water passing thru. So your design will lessen the pull on the float under the same conditions. Still the question should be how well it catches fish!

Is it possible that leaving 10% remaining in the water isn't such a bad thing? Could it be that only taking a portion of each population so there are some left to repopulate ....is more sustainable and good long term planning (ecologically and business wise)?

.

If there is no risk of capturing an entire distinct population (I am really just brainstorming, so forgive me if I was off base), perhaps you could create a modified design, either for demonstration purposes or to sell....

By replacing the wider mesh section with the very widest practical mesh (so that the form is maintained) and then attaching long socks of finer mesh across the wide mesh opening (such that there is enough mesh surface area as to create little restriction to flow), perhaps you can quantify how many fish typically pass through the wider mesh sections?

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This still won't demonstrate any problems the competing all fine mesh design has with losing fish as the float is pulled under.

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If placing a long sock over a section supported by very wide mesh is not entirely impractical, maybe this could free your design to place the high flow sock other places that might be advantageous.

Perhaps having a high flow section at the very top, just behind the float would allow an improved net position AND the ability to see when schools are being forced into the high flow sock...

Thank you for the synopsis.

the wider mesh is called Guard Mesh and actually lies parallel to the bottom sediment.

Fish pass over this in .25 of a second, and never even know there is a 3/4" gap there.

These are sampling nets and used solely for the purpose of sampling fishes both native, exotic and endangered. Most of what is caught is measured, photographed and returned unharmed to their natural environ.

Losing 10% is a wide estimate and hard to determine sometimes. Certain conditions make it impossible to catch even 75% of what is there. However, my aim is furnish as best of a gear possible so that when reports are made, the scientists can say without concern, that they captured as much of the target species as was possible in THAT locale.

Usually these "V" seines are deployed and pulled for 25 meters or less.

I make about 55 different gears for capturing Young of the Year fish (Y.o.Y.)

This gear is about 12-15 years old and few have ever questioned its catch-a-bility until now.

I just wanted to get some 'educated' discussion on the use of the guard mesh as opposed to the solid fine mesh nets, which suck so much water they are hard to pull and produce such a belly ( Drag Quotient) that the lead line comes UP and the float line goes DOWN. When dealing with folks with limited knowledge, its always best to overwhelm them quickly with facts before they start assuming....and you know what that can lead to.

thank you and all the others.

Put it in a CR4 "Newsletter Challenge", and when you get an answer sufficiently convoluted to bamboozle satisfy your troll, name that person the winner!