Future Ships Could Float On Bubbles

MattSparkes writes, "Creating a layer of bubbles underneath a ship's hull could improve fuel efficiency by 20%. When you consider that 90% of the world's goods are transported by sea, the importance of this discovery is obvious. 'Conjured up from thin air at the flick of a switch, this slippery blanket will help transport a fully laden tanker or container ship across the ocean at higher speed, and using far less fuel, than ever before... There is currently no other technique in naval architecture that can promise such savings.'" The article looks in some detail at the engineering problems that will need to be overcome before this technique is practical.

But how will it affect buoyancy?

[with_him]

Since methane hydrates releases are still suspected in the sinking of ships, how do the researchers account for the loss of buoyancy? Since this research calls for redesign of current ship building know-how, how are they planning on addressing the buoyancy part of the equation? To read more check out this http://www.newscientist.com/article.ns?id=dn1350 [newscientist.com] and http://jbj.wordherders.net/archives/000992.html [wordherders.net] someone trying to weaponize the buoyancy concept. http://www.nexusresearchgroup.com/fun_science/buoy ant1.htm [nexusresearchgroup.com] A fun science experiment for the kiddies, or others that want to understand it better.

Re:But how will it affect buoyancy?

[DilbertLand]

With methan hydrate releases the theory is that the entire volume of water surrounding the ship is "full of bubbles" and has an effectively lower density. What they are talking about here us just surrounding the hull with a thin layer of bubbles.....maybe the ship sits a couple inches (to pull a guess out of my rear) lower in the water....but there's not going to be any danger of sinking a ship...

In case anyone is interested

[noewun]

In what

The idea of air cavities has much in common with supercavitation, in which a submerged object such as a torpedo creates a single large bubble around itself. This slashes skin friction, bringing remarkable speeds within reach (New Scientist, 22 July 2000, p 26). Perhaps not surprisingly, Russian engineers who first developed supercavitating torpedoes have not only done plenty of research on air-cavity lubrication for ships, but have also put their ideas to work.

refers to: Shkval [fas.org]. Scared the bejesus out of the U.S. Navy.

This works best at slow speeds

[nels_tomlinson]

I haven't yet read the fine article. I do know just a bit about naval architecture. This should help with skin friction, which is the big deal at low speeds. For higher speeds, the resistance which comes from making the wake is the big deal, since the wave-making resistance increases roughly as the square of the speed.

So, what's ``low speed?'' That's probably going to be any speed much below sqrt(waterline length in feet), with units of knots. So, for a 400-foot long ship, anything less than 20 knots is in the speed range where this is likely to matter. For a 900 footer, anything less than 30 knots. Most ships travel in that low speed range, so this could be practical.

Yes and it has been in use for a while

[LWATCDR]

http://www.fas.org/man/dod-101/navy/docs/swos/stu2 /NEWIS9_7.html [fas.org]
Some people will confuse the idea of bubbles with cavitation. Cavitation is loud and is avoided but it is caused when a screw manages to cause a phase change. The water turns to vapor and the the bubble collapses making a lot of sound and can even erode the metal on the screw.
The bubble of air that the navy uses don't collapse so no noise instead it acts like an insulator.

I wonder if you could use the exhaust gases of the ship for the bubbles for shipping application? You would have to cool the gas first but it might be a bit if a free lunch.

Not really the same.

[Poromenos1]

The supercavitational bubble is vacuum, not air. This is also the reason why the torpedo cannot be manoeuvred with traditional means once fired (since there is no water anywhere around it).

Re:Not really the same.

[PWNT]

The supercavitation bubble negates the need for torpedoes that can steer.

Ships move slower than traditional torpedoes, however the relative difference is not huge, so a ship can attempt to evade the torpedo.

These new torpedoes travel so fast, that any amount of evasion is useless! IIRC the new torps are travelling at 200 knots, like 400 km/hr or something. This is a huge difference compared to older slow torpedoes travelling at 50 knots.

These very fast torpedoes would be used to sink the larger fleet carriers from submarines. Get under or anywhere near the carrier, shoot 3 at the carrier and go on a silent run to creep away.

Vikings already did it

[TeknoHog]

TFA says the most promising method of getting the air cushion is to build cavities on the underside of the ship. It takes some energy to maintain the cavities full of air, but it's a lot less than the energy required for the other methods.

However, the Vikings used the same principle centuries ago. Their way of building ships [wikipedia.org] creates longitudinal grooves along the bottom of the hull, which form cushions of air at higher speeds. The overall shape of the hull also contributes to low resistance. I don't have any proper references, as I only saw this in a documentary once, but for example here [imperialoil.ca] is a brief mention of the idea.

Has been at least speculated for a long time

[TheAxeMaster]

There has been a lot of theorizing that this is how some of the viking longships were so fast. Essentially the way the planks were laid out allowed the ship to catch air from in front of it and shove it underneath the boat, guiding it along its length. Look up the Gokstad ship for details.

Re:Nope

[Ungrounded Lightning]

To sink lower, the ship would have to move [the bubbles] aside - which it is already doing - but are limited in their ability to move by the resistance of the surrounding water. Meanwhile they are continuously replaced from the air source.

To make it clearer: If the boat sinks further the layer of air goes with it and stays about the same thickness. What is displaced is water. So the craft remains bouyant, as if the layer of air were part of its own structure, rather than part of the supporting water.

In fact, because the layer of air is "part of its own structure" and displaces its own volume of water, the craft itself will float HIGHER by about the thickness of the layer of air. (The air will be somewhat compressed and thus denser than the atmosphere, so it will raise the ship by a smidgeon less than its own thickness.)

Re:Not really the same.

[Anonymous Coward]

These new torpedoes travel so fast, that any amount of evasion is useless!

They are so fast you can't "see" them coming on sonar. LIDAR doesn't have very good range under water and RADAR doesn't work at all. If it was fired from enough below the surface that the shock wave doesn't hit the surface before you're hit, you'll never know it was coming.

Re:no other technique???

[merreborn]

How large of a sail would it take to provide worthwhile trust to a 100,000 ton container ship, I wonder?

A 170 ton Schooner uses 700 square feet of sail...

Assuming a linear sail:weight relation, that'd mean 400,000 sq feet of sail. Over 600 feet square. I wonder how your average sail material would hold up when scaled that large; additionally, what sort of mast and rigging would be required? How would you adjust the sails, anyway, when the deck is covered in thousands of 40 foot containers? Would all of this merit the additional weight?

Oh, and on top of that, a container ship travels twice as fast as a schooner.

http://en.wikipedia.org/wiki/Shenandoah_Topsail_Sc hooner [wikipedia.org]
http://en.wikipedia.org/wiki/Emma_M%C3%A6rsk [wikipedia.org]

Were sticking a sail on a container ship practical, they'd probably have done it by now.

Flapping Tails

[Garrett Fox]

It's also worth looking at MIT's RoboTuna and RoboPike [mit.edu], robotic fish, and the penguin boat Proteus [mit.edu]. These projects demonstrate that fish-like fins or flippers substantially improve propulsion efficiency vs. propellers, because they generate vortices of water that actually push a vehicle forward. MIT sees these vortices as the answer to Gray's paradox [arstechnica.com], which said that a dolphin would have to be stronger than it is to swim as fast as it does. (That article disagrees.)

A flapping drive would also have the advantage of looking cool.

Re:Not really the same.

[Anonymous Coward]

As strange as this might sound, VA-111 (Shkval) is a defensive weapon. You cannot use this to destroy a mobile target, just force it to move away (hopefully rapidly enough to rupture its links to towed sonar sonar array, torpedoes, etc.)

Re:Vikings already did it

[Norbury]

And Sir John Thornycroft built models to prove it in the 1870s. And every 5-10 years somebody re-invents it and it doesn't work at large scale then either so it just joins an ever longer list of improvement patents like these 1412848 Apr., 1922 Dunajeff 114 / 289. 2005473 Jun., 1935 Sanden 440 / 44. 3261420 Jul., 1966 Schmidt 180 / 122. 3590762 Jul., 1971 Yuan 114 / 275. 3827388 Aug., 1974 Fulton 440 / 44. 3871317 Mar., 1975 Szpytman 114 / 282. 3968762 Jul., 1976 Meyer, Jr. 114 / 278. 4166515 Sep., 1979 Tattersall 180 / 119. 4345538 Aug., 1982 Warner et al. 114 / 274. 4660492 Apr., 1987 Schlichthorst et al. 114 / 67. 5339761 Aug., 1994 Huang 114 / 274. 5626669 May., 1997 Burg 114 / 67. 5860383 Jan., 1999 Whitener 114 / 271.