Speed of Descent

I get 2.5 - 5 hrs...I would take it out and mark 100' of line and use a stopwatch to see how long it takes to play out the 100' of line....then multiply by 170...

https://www.quora.com/How-fast-does-an-object-drop-in-water

At optimum free-falling rate... 47 - 57 minutes...

But the tether is made of reinforced spider silk with an unobtanium core.

As I consider this valid point I wonder:

Might the tether line overtake the payload? If yes, could it become snarled in the tether line if allowed to freespool?

PW Slack mentions spool resistance as an undefined variable.

So will you be dredging the ocean floor now?

1. This is the updated information I have on the use of my gear.

2. I was told that the net I built will have 1250 lb. of Bollard Pull ( at 2 knots of speed in a Test Tank).

3. Once again, any idea of how long it would take this rig to hit bottom? I realize there are numerous unknown factors. If possible a reasonable guess....anything is better than nothing.

* Yes, the cable alone will weigh a ridiculous amount*

It seems to me, if deployed as pictured, that the net will act as a parachute slowing the descent considerably....This seems like the boat would move quite slowly allowing the net to sink behind but with enough movement to keep everything in alignment, so the gear would drift slightly forward and downward as the line is played out behind...Is the line played out from a drum at a certain speed, or is it allowed to free fall....? ...and the measurement, is it straight down, or is this the amount of line dragging behind the boat?

OK I just saw the 50,000 ft of line....Wow the scope of this is blowing my mind..what is the type and size of line being used?

The net assembly could be encased in a streamlined missile shaped enclosure to speed descent, possibly with a water soluble attachment that dissolved and freed the net after x amount of time.....The enclosure itself could be water soluble plastic perhaps, or it could be tied with water soluble bands every ft...just spitballin'

3/4" cable I believe. I am trying to move them into UHDPE line of same diameter.

It says 25mm on the drawing: that's 1"

Netmaker, is it desired to get the rig down as fast as possible, or will you live with whatever the number of hours ends up being?

The drag from the trawl will be an enormous impediment if the rig is simply dropped into the water as drawn. Can some sacrificial mass with a release be fitted to the cone end?

No... they asked me what I thought. I have no real clue. My preference is a steel beam with sleds ( Misago Beam net). one solid unit, 1600 lbs. ...the customer wants to use a trawl net.

This was very successful .....but the customer would like a Trawl system

Wow, what a simple idea! Nice.

I wonder if there is benefit to taking this idea one step further. If the spooler is not the limiting factor then consider having the overall net assembly shaped/coupled to produce a downward force when pulled forward. This configuration could keep a taut tether (won't snap when slack taken up) and increase deployment speed. For recovery stop the boat and the down force is gone.

The customer has very specific gear on board and I can not suggest too much variance. they just wont be able to do much else.

YES! That makes more sense as there are soooo many variables here.

This link ( gigacalculator.com/calculators/terminal-velocity-calculator.php ) will allow you to calculate the terminal velocity. At that depth you need to use a density for water of about 1.06 but increment this value for each calculation as the depth increases. 0.3 looks reasonable for the drag coefficient but repeating for 0.2 & 0.4 will give you a range to work within. I would do a calculation for every 1000ft increasing the weight at each depth to allow for the tether, then average the speed between adjacent depths to work out a time for that 1000ft and sum all the times. For the first 1000 ft assume that terminal velocity has not been reached and double (total guess) the calculated terminal velocity time.

Bear in mind what would be a sensible maximum rotation speed for the tether spool. It may be that you will have to limit the speed of decent to prevent bearing overheating or for health and safety considerations.

I'd suggest that for a first estimate you go with 2 knots.

Looking at your picture the average slope of the whole apparatus is about 20^o; so that's 50,000 feet at 12,000 feet per second: just over four hours.

The time for it to hit the bottom will be directly proportional to the cost to replace the device when the tether fails or snags or if the tether is extra strong then the rapidity with which the trawler will pull itself under the water and pass the net on the way down,

Maybe insure it against water damage?

There is a 7-% chance4 the net will snag up and never see the surface again.

Wow, what do you catch with a net at 17,000 feet?

That is quite possibly the purpose of the mission.

Aliens.

The unknown...

My guess is that whatever you catch might not fare too well at a pressure that is 0.2% of what it is used to...

Not much...but what you do catch is very interesting.

Here are some answers..

Daily one of a kind seafood specials ant NetMakers roadside cafe!

That middle top picture looks a lot like Kenny, mmkay...

Kenny's on the menu!?

Oh my god! They killed Kenny!

How would one know when the <...device...> had arrived at <...the bottom...>?

The politicians will call and let him know.

The most accurate, simple method would be a pressure sensor on the payload and telemetry cabling back to the boat.

...which adds to the weight of the <...tether...>, and influences the fall rate...

A sensor on the net.

Simple as it sounds in concept, it still does not seem totally legal in its consequences, to me...

It is bonafide research work. No big pay loads. No,lengthy on bottom time. yes, quite legal according to all national and international research work.

What interesting work netmaker gets to do. I always try to offer a little engineering advice to him because he generally spits a little back to us of what he sees. What he does is not always in the books, it's sometimes on edge, and kinda cool. These are real world problems that mostly don't have answers. Only on CR4. Thanks netmaker....oh and thanks CR4.