View Full Version : Mariana Trench and a fishing line.

6th May 2013, 00:35
Myself and Mrs NMC were talking about the Mariana Trench this morning and I said that I'd love to be on a boat and drop a line in to see if I could get it to the bottom of the Mariana Trench.

Now, she said that you would need a very heavy sinker thinking that at great water depth the density of the water would prevent the sinker going past a certain depth.

Any truth to this notion?

I was wondering how would you know know if you actually hit the bottom.

6th May 2013, 00:48
Now, she said that you would need a very heavy sinker thinking that at great water depth the density of the water would prevent the sinker going past a certain depth

Your wife's thoughts, understandable as they are, are somewhat whimsical...

Seven miles under the sea | walsh, regret, miles - Features - Victorville Daily Press (http://www.vvdailypress.com/articles/walsh-18116-regret-miles.html)


6th May 2013, 00:49
From what little I remember from my college days, the density of the sea doesn't increase too much irrespective of the depth.
It will change slightly due to the temperature drop and the salinity change, but I can't see that it would have any noticeable effect on something like a fishing weight.

What would probably have far more effect would be the currents dragging your fishing line which may make it almost impossible to know when your sinker was on the seabed.

What might also be a problem would be the weight of about 6 miles of fishing line. Even though it would have a lot of boyancy, there would still be a lot of strain being put on line at the reel/winch.

6th May 2013, 00:55
That came from an old mariner's tale that a boat would only sink
to a certain depth and remain suspended when the water density
reached a certain point.

You'll need a good 36000 foot fishing line to reach the bottom of
the Mariana, so I'd get the strongest line on the market!

6th May 2013, 01:45
And should you find the gear needed to plumb the Trench, you might come up with a 500 lb. squid on the end of your 10 lb hook. What're you gonna do?

6th May 2013, 01:46
So lets think about this:

At 1 ATA, sea water has a density of 1.02 and lead has a specific gravity of 11.35.
For all intents and purposes, liquids and solids are not particularly compressible, and to what little extent they are, it's probably safe to assume some proportionality.

So: at 2 ATA, (32 ft of sea water, (more or less 10 meters), there is twice the pressure as at the surface. At 100 meters, there is about 10 atmospheres of pressure, acting on everything, and at 36,000 ft (1, 125 ATA), there is just as much pressure on the water as on the lead sinker. Both of them weigh just as much relative to each other as they did at the surface. (just about).

So things should keep sinking just fine.

I'd advise using monofilament nylon, as it's more or less isodense with water.
Flourocarbon or braid is a lot denser, and seven miles of anything weighs a bit.

Oh, by the way.. at th the surface, we're living under 14.7 pounds per square inch of pressure. at th the bottom of the Challenger Deep, it's around 16000 pounds per square inch..

(check out google images with deep submersibles and see the styrofoam cups and trinkets they take down for fun)

6th May 2013, 01:47
Yeh but the 500lb squid will emerge from the sea with its guts inside out.

6th May 2013, 02:13
(check out google images with deep submersibles and see the styrofoam cups and trinkets they take down for fun)

Take it from me that some of these tricks do get out of hand at those pressures.

I had a coffee cup that turned into a thimble and would sink when placed in a glass of water. We to used write little missives on the sides in ball point and when they came back up you needed a magnifying glass to read them

Buster Hyman
6th May 2013, 02:18
Beware of Russian subs with Scottish Commanders! :ooh:

6th May 2013, 02:52
NMC - Mrs NMC's argument is a typical example of utilising female logic. You can beat this argument by stating that only men know about important stuff like weights, gravity, fishing, what makes a car or plane go, and reading and understanding maps. :)

tony draper
6th May 2013, 07:14
Think I posed a question here once as to how long it would take a cannon ball flung over the side at that locale to reach the bottom,one misremembers if I got a answer now.

Lon More
6th May 2013, 07:24
Tie it to the tail of an Air France Airbus and wait.

edited to add- I think it's named after an ex-girlfriend. I never reached the bottom there either.

tony draper
6th May 2013, 07:40
Well they do have plenty cannon balls, mostly ours.:rolleyes:

6th May 2013, 11:57
To increase the density of seawater it would have to be compressed.
That's not easy to do with liquids, otherwise hydraulic systems wouldn't work.

Edit: This is what happens when hydraulics do fail...


6th May 2013, 12:01
I thought Mariana Trench was a porn star.

6th May 2013, 12:15
From Wiki (http://en.wikipedia.org/wiki/Mariana_Trench):-
The Mariana Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands.The Mariana Islands were claimed by Spain in 1668. Spain established a colony there and gave the islands the official title of Las Marianas in honor of Spanish Queen Mariana of Austria, widow of Philip IV of Spain.
At the bottom of the trench the water column above exerts a pressure of 1,086 bars (15,750 psi), over one thousand times the standard atmospheric pressure at sea level. At this pressure the density of water is increased by 4.96%, making ninety-five litres of water under the pressure of the Challenger Deep contain the same mass as a hundred litres at the surface.
The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is not a perfect sphere: its radius is about 25 kilometres (16 mi) less at the poles than at the equator. As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth's center than the Challenger Deep seafloor.

6th May 2013, 12:30
I guess hopping a lure along the seabed is out of the question then...I mean, how would you know you got a bite?

6th May 2013, 12:43
"I thought Mariana Trench was a porn star. " no, that was Mariana Tench, but she wasn't popular with her co-stars: poor personal hygiene left her a bit fishy

6th May 2013, 13:28
Sallyann1234 - Sorry, the tipper "mishap" is most definitely not a hydraulics failure. It's an out-of-level tipping failure. The tipping trailer was parked on ground that has a slight cross slope on it.
Upon raising the tipper body, the elevation of the C of G of the load reaches a point where the C of G moves outside the wheel track, and the tipper body falls over.
As it goes over, it fractures the tipping hoist - and in this case, the body broke free from its pivot points on the trailer chassis.
Quite often, the body and chassis stay attached, and the body takes the trailer chassis with it, leading to some major chassis twisting.

It's quite a frequent occurrence with semi-trailer tippers, and is caused purely by the truck driver not selecting a perfectly level position to dump his load.
I knew one company that used to lose a tipper a week in this exact manner, because they employed anyone who could hang on to a steering wheel - rather than professional drivers with the appropriate skills.

6th May 2013, 17:32
Thanks for the correction. Very interesting. I'll make a point of keeping well clear of any tipping trucks :)

6th May 2013, 17:36
or shouldn't that be tippling trucks?

Windy Militant
6th May 2013, 19:52
The driver obviously used to work on the railways as tippling trucks was a standard practice
Tippler unloading wagons - YouTube

edited to add steel shot must sink or the Trieste bathyscape would not have reached the bottom.;)

6th May 2013, 20:18
edited to add steel shot must sink or the Trieste bathyscape would not have reached the bottom

It also wears the bejezzuz out of brass marine pumps :)

tony draper
6th May 2013, 20:52
I believe the steel shot was to enable Trieste to get back up again,it was released on the bottom no pumps needed, it just ran out under gravity which still works even at that depth,

Um... lifting...
7th May 2013, 00:38
The floaty bits in Trieste was filled with petrol, which makes no sense when one considers Trieste had no powerplant of any kind, but a mite more sense when one considers the incompressibility of liquids, their specific gravity and whatnot.

The steel shotty bits were held in place in what were basically inverted buckets thru the use of an electrickical magnet pow'rd by batt'ries.

In event of an electrickical failure, the shot tumbled out and up she come.

7th May 2013, 03:16
In event of an electrickical failure, the shot tumbled out and up she come.

When all else fails (entanglement and electric failure) the crew has a guillotine to sever it's attaching cables to the submersible. The sphere has enough buoyancy to float, although how long it takes and where the currents take it is another matter.

I think if you look back in its history you will find the event where a wayward bubble of air in a battery vent tube, trapped by a closed valve, caused the metal battery covers to collapse on the main battery causing a loss of power. This was overcome by a last chance battery. The crew was not happy about the cause. The navy takes a dim view when an ensign flagged vehicle stays on the bottom even if the crew escapes.

One of the problems with the shot system is that to maneuver near the bottom in mountainous terrain they have to constantly give up shot and take on sea water to go up and down until they near a critical mass. At that point they decide to land (on top of the water). Then for subsequent dives the grunts on the mother ship spend about 24 hours reloading a ton of the steel shot by hand (the brass pump idea didn't work longer than a half hour) :)