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back to article Hot bodies get super-slippery when wet

An Australian boffin says he has come up with a novel method for making things such as ship's hulls or torpedoes slip through water more easily. Professor Derek Chan of Melbourne uni suggests that it would be practical for ships to exploit the "Leidenfrost effect", named after its discoverer in 1756. This refers to the behaviour …

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WTF?

Haha.

Heat up the hull of a container ship to "significantly more" then 100 degrees Celsius whilst it's submerged in ocean water.

They thinking of including Nuclear reactors on them now? I'm pretty certain that they're the only things that could even come close to the necessary power output.

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Anonymous Coward

Maybe not the whole hull

How about if it was coated with a film which could be heated quickly but was itself a good insulator? I'm sure trickier materials problems have been solved getting vessels into space in the past.

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Joke

Think green

Scratch the nuke and make it tide-powered.

Anyway, I'm off to get a bucket of nitrogen and a lawyer...

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FAIL

^This

I'll take some convincing that this idea (which only applies in open seas where thrust is worth more than manoeuvrability, I suspect) can actually reduce overall emissions.

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Alert

Boiling the ocean

Literally too

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Anonymous Coward

If only nanotubes weren't prohibitively expensive...

see title

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G2

firefly

Burn the land and boil the sea,

you can’t take the sky from me...

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Heating the boat's hulk.

We do not need any other heating system,. These boatscarry coal to Japan. All what they have to do set fire to it. The Ship will go so fast that there will be at least 10% left for Japan.

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Paris Hilton

Hot Slippery Bodies

Why do we need a professor to tell us hot bodies get slippery and wet? It's common knowledge.

Paris, because she also gets slippery and wet easily.

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mmm

May be this is news for the professor?

R

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torpedo

I'm sure there are some naval ordnance techno boffins out there who can put me right on this, but I would have thought the cavitation from all the escaping vapour would make for a hell of a noisy torpedo, which I would expect to cancel out at least some of the speed advantage.

Also how would the necessary temperature be maintained? Onboard equipment would take up space and fuel, which would presumably limit range and warhead size.

Over to the people who claim to know what they're talking about.

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Black Helicopters

@ torpedo

As a former junior naval ordnance techno boffin, I can assure you that the intended victim of a torpedo generally - and in the case of a submarine, certainly - knows it's coming the moment it's launched and immediately takes evasive action. No amount of additional noise makes a difference to the target once the fish is on the way, but a few seconds less time to evade or distract it certainly does. The noise may affect the torpedo's ability to identify a target by its acoustic signature, but that feature is most important for devices that sit quietly and spring into action when they spot a target - self propelled mines, in other words - and there are clear practical problems with keeping a loitering torpedo hot.

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Anonymous Coward

Oh,

and of course I was talking about "normal" supercavitating torpedo, which doesn't need all that heating.

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Boffin

It can go

at 250 mph, and there are (classified, but in principle workable with some degree-level physics) some ways to reduce the noise.

But do you seriously think that at this speed, the noise matters?

Typical range over which you want to use torpedo is at most 5 miles - do you really think a big ship can do much in around 2 minutes it takes supercavitating torpedo to reach it? Especially if it's got some sort of guiding system?

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Stealth torpedo

Afaik torpedoes generally swap stealth for high speed.

Stealth torpedoes are normally called mines and are fairly stationary.

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Speed is life

The Russian rocket powered torpedo thing basically goes in a straight line very fast, the idea is it's so fast that the target vessel would be unable to alter its velocity enough to avoid a collision. The videos I've seen of them (they're on youtube) show a massive wake on the surface so it's by no means a stealth weapon however you look at it . I don't think the range isn't that great either and they're designed to be launched by surface vessels rather than submarines who'd just end up with a trail of bubbles pointing to them.

Of course the other problem they have is there's no real way of guiding them as they generate too much self noise for sonar to work, although wire guidance might be an option, in which case the counter measure is to take out the launch platform.

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Anonymous Coward

Not on submarines?

Remember the "Kursk affair" a few years ago?

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Just don't use...

...heat-sensitive payload or fuzing on your torpedoes!

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Pint

A La Cartman

It's my hot body. I do what I won't.

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Mushroom

He's been watching Mythbusters

http://www.youtube.com/watch?v=UZio0f7fP04

Skip ahead to 6 minutes in.

(Explosion because... well.... Mythbusters!)

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Anonymous Coward

You are kidding.

"The same effect can also allow a person to put their hand into a bucket of liquid nitrogen without harm."

You go first and then maybe I'll believe you.

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PT

Yes he's kidding

I was sitting on the floor half under a machine once, when someone knocked over a liter beaker of liquid nitrogen. I can confirm that the "Leidenfrost effect" works very well for LN on a tiled floor, causing it to speed about and rapidly cover the entire room, but fails utterly when the LN encounters the seat of a person's pants.

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Boffin

LMGTFY

http://www.youtube.com/watch?v=gjsMV1MglA4

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Anonymous Coward

I didn't believe it

Until i saw it done, it's the same effect that enables someone to gargle liquid nitrogen.

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Headmaster

In Which I Fully Submerge My Hand in Liquid Nitrogen

Popular Science did a cool (get it?) article about this some time back, complete with video, heres the link: http://www.popsci.com/diy/article/2010-08/cool-hand-theo

he wussed out on the molten lead experiment that Mythbusters did though.

Naturaly it ends with "ACHTUNG! Do not try this. If liquid nitrogen soaks into your clothes, you will not be protected by the Leidenfrost effect, and you can get frostbite very quickly."

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Boffin

A bit wide of the mark

I'm reasonably sure I saw a professor pour it over his hand, and briefly cup some in his palm, giving the same explanation. I suspect that he'd have stuck his hand into it if it had been safe to do so. This was ~20 years ago when 'safe' had a slightly different meaning.

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WRONG

I have spent a lot of time playing with liquid nitrogen in the lab, and I can tell you the one thing you DO NOT want to do is "dip your hand" into it. You will lose it, quickly, because the pressure of the liquid rapidly displaces that thin boundary layer.

What you can do quite safely is pour it all over you - as long as it has a path to run. You can take a Dewar flask of it and pour it all over your hands, arms and legs...as long as you are not wearing gloves or shoes that will trap it, and thus allow it to burn-through the vapour barrier.

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Alert

hand into a bucket of liquid nitrogen without harm(!)

like AC above I have serious dobts about this also!

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Coat

Pants

Your pants ruined the effect. Had you been naked, it would probably have worked fine. Cloth is just about the worst thing in this situation, since it actually soaks up the LN2 and holds it close to your body.

Icon: Liquid Nitrogen Work Area - Undress For Safety

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Joke

Title too long...

"The same effect can also allow a person to put their hand into a bucket of liquid nitrogen without harm."

You first :)

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A typo, I suspect

It allows a person to leave their hand in the bucket without arm.

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Boffin

Mythbusters went first so I don't have to

Actually, they dipped their fingers and hand in molten lead - perhaps an even more frightening prospect (though they didn't keep it in long). Skip forward to about the 2 minute mark.

http://www.youtube.com/watch?v=UZio0f7fP04

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Happy

ultrasonics

I thought that correct frequency vibrations would create the same effect at a much lower energy cost than the 400+C required.

I like the idea of the russian gas injection design.

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FAIL

Fish'n'Chips

This is a great idea. We should start removing salt from the ocean immediately so it stops clogging up the Leidenfrost effect on ship hulls.

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Anonymous Coward

Corrosion unlikely to be a problem

in torpedoes at least, given their hoped-for lifetime once activated.

On the other hand it would possibly provide a solution to any that fail to hit their intended target, rather than just bobbing around they could neatly degrade so that no passing children (kids snorkelling) will pick them up and think "shiny toy!" and find they've entered a sudden weight loss program.

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Facepalm

Mwahahahaha

"The ship's hot body could substantially minimise the amount of drag as it passes through water, therefore potentially reducing transportation costs and greenhouse gas emissions."

Is that supposed to be a joke? If not I have another great idea: to reduce costs and greenhouse gas emission, Australia could ship it's ore and grain using Endeavour instead.

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Why?

Coal doesn't go off and the life of wheat stored under proper conditions is months or even years. Why do these freighters need to go faster?

I think he's also forgetting the realities of the shipping market which is to reduce costs as far as possible by only ever using very old, single hulled bulkers manned by third world crews sailing under flags of convenience. Only a few years ago, one of these monsters was sinking every month and no one in power gave a toss until the MV Derbyshire vanished, but since then, nothing's changed.

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Boffin

Safety first

I would suggest amending this sentence:

"The same effect can also allow a person to put their hand into a bucket of liquid nitrogen without harm"

True, but only if they dip their hand in and out VERY QUICKLY. I would highly recommend not casually sticking your hand in a bowl of liquid nitrogen and saying to your mates "Look! This won't harm me!"

The same trick can be done with hot oil - IF you wet your hand with water first. Dip it in quick enough and the steam will allow the oil to run off before you get burnt. Still - not to be tried at home - you need to do it VERY QUICKLY, and this is NOT enough time to grab a dropped ring from the bottom of a hot deep fat fryer!

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Corrosion?!?

" the effect of increased heat on corrosion."

I wouldn't worry too much about the effects of faster corrosion on a torpedo since I would think that their expected working life is measured in single digits of minutes

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Meh

Global warming?

Nawwwww..... Lets just heat up the oceans so we can get our cheap Singapore hatchbacks quicker...

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Anonymous Coward

Not so brilliant idea...

Question... What happen when a ship gets on top of air bubbles? The answer, it lose it's buoyancy and sink right away! This is a true fact, and it did occur in the past.

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Boffin

@AC

That only happens if the ship is above an area where the water itself _contains_ a lot of bubbles, the whole point of this piece is that you are only dealing with a boundary layer, so the density of the water is _not_ affected.

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Pint

The SodaStream (tm) Defence

So you could divert the hot torpedo beneath you if you fired something fizzy in it's direction?

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Anonymous Coward

Don't try this at home kids!

"The same effect can also allow a person to put their hand into a bucket of liquid nitrogen without harm."

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Go

It is possible

I have done this many times. Being a PhD chemist I had plenty of access to liquid nitrogen when in the lab and it is useful for lots of capers. I should add that I was never brave enough to hold my hand under for more than a second - but a dip in and out is perfectly fine.

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Childcatcher

It won't work

Pushing a ship either through or over the sea is vastly different to watching a drop of water dance about on a spoon heated over the gas cooker (I done that as a child, fire is great!).

If they're planning to ease the ship through the water, as ships move currently, then surely most of the resistance is due to moving the large bulk of water out of the way of the ship, and putting it back after the ship has passed. This won't change that.

If they're planning to ride the ship over the top of the water, then surely the waves will scupper that one.

Either way, sea salt will be deposited on the ship's hull, which won't help.

Even if the vapour layer does insulate well, warming the ship's hull up in the first place will require insane amounts of power.

This whole thing is just about as stupid as an article I once read in new scientist about supercavitation. The suggestion was to reduce the drag on an underwater passenger craft by going fast enough using rockets to cause deliberate cavitation at the rear of the craft. Not crashing into things like whales and other submarines would be difficult at several hundred mph, even if it did reduce drag.

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Joke

Maybe at launch?

Heat the hull up in dry dock before each voyage?

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Happy

You go first

The Leidenfrost effect is real. I happened to demonstrate it a few months ago while doing some plumbing work. I'd heated a leaky value to a temperature, high enough to melt solder (not the Lead-Tin variety, but the new and improved variety that has to be used on Copper pipes now, which requires even more heat to melt). I removed the value with a pair of pliers, and laid it aside. Then, in a bout of forgetfulness, I reached over and grabbed it with my bare hand. There was an incredible amount of sizzling, as the water on my fingers evaporated, but, quite surprisingly, I didn't get burned (although I did drop it pretty quickly, when the sizzling reminded me that it was probably 200 degrees C!).

As for making torpedoes move through water faster/more easily, why don't they coat them with teflon? Or, maybe they should add a soap dispenser to the front of them to give them a coating of soap? Or, maybe add an air bubbler to the front of them? What other slippery things are there out there that could be used? Those might be cheaper than trying to heat them well above 100C.

Dave

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Boffin

Would it really work for a floating vessel?

Not that this is my area of expertise, but wouldn't creating a gas layer under a floating vessel cause the vessel to fall into that void, eliminating its buoyancy?

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Lets see...

You want the British Navy to fill a metal tube with 650 pounds of Torpex high explosive, then heat that cylinder to 800F. Riiiiiiight...

Please step through this door Sir. Some large lads from the Security Service would like to have a chat with you.

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