New Ship Will Remain Stable By Creating Its Own Inner Waves

Zothecula writes "When offshore oil drilling rigs are being installed, serviced or dismantled, the workers typically stay in cabins located on adjacent floating platforms. These semi-submersible platforms are towed into place (or travel under their own power) and then their hulls are partially filled with water, allowing them to remain somewhat stable in the pitching seas. Now, a ship is being built to serve the same purpose, but that will be a much more mobile alternative. It will keep from rolling with the waves by generating its own waves, inside its hull."

It's about time

[Anonymous Coward]

I used to do that in my bathtub. It's nice to see someone finally upscaled it like this.

Re:

[K. S. Kyosuke]

It's nice to see someone finally upscaled it like this.

I'm trying to imagine an ocean-going ship stabilized by upscaled ACs rolling in tubs and the first thing that comes to my mind is "it's 1912 all over again!"

Re:

[davester666]

Are you sure the AC wasn't talking about something bubble-related?

Need that for my water bed

[JoeyRox]

To helps me gets my grooves on without losing my babe inside the folds of my water bed.

Re:Need that for my water bed

[gsgriffin]

I'm glad you clarified 'folds' as being a part of your bed and not you.

Power requirements?

[danceswithtrees]

The system pushes water from side to side using compressed air to counteract rolling from ocean waves. Granted this is for use in drilling rigs (read big money), but I wonder how much power is required to run the air compressors. The compressors have to be high flow to rapidly move a lot of water, albeit at relatively low pressures-- only 4.4 psi required to generate 10ft difference in seawater (this does not take into account viscosity and inertia).

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[Anonymous Coward]

The system pushes water from side to side using compressed air to counteract rolling from ocean waves.

The two articles linked above both say the waves move the water and air valves are used to control that movement. I read that as this is a passive system fine tuned by controlling the rate air can escape and reenter at the ends of the U shaped tubes. I don't see any links to more details.

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[Charliemopps]

It doesn't take a lot of power. Aquarium guys do it all the time.
http://www.youtube.com/watch?v=QHfDh4eqYPs [youtube.com]

I doubt the system can make quick changes though so a violent storm or rouge wave couldn't be compensated for. But steady constant waves would be easy.

Re:Power requirements?

[danceswithtrees]

That is a different problem and not a fair comparison. The wave in an aquarium is being stimulated at the natural resonant frequency. If you slosh the water in a tank without the wave device, it will go back and forth at its natural frequency losing a little bit of energy with each slosh. In much the same way that you can maintain the swinging of a heavy pendulum with very little energy, the wave thingy you reference is energizing the wave at the natural frequency of the tank. If you were to try to make waves at 70% or 124% of the natural frequency, I think it would take MUCH more energy.

You can't reasonably expect the ocean to rock the boat at the resonant frequency of the internal water tanks. Therefore the ship's internal wave system is going be expending a considerable amount of energy. Ships weigh tons. To counteract the rolling motion of a several ton ship, you are going to have to move several tons of water several times per minute.

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[jbengt]

You can't reasonably expect the ocean to rock the boat at the resonant frequency of the internal water tanks. Therefore the ship's internal wave system is going be expending a considerable amount of energy.

You can if you tune the resonant frequency of the tanks to the general frequency of the waves and use the air valves TFA talks about to fine tune the resonance. I know, for example that tuned water tanks are sometimes used to dampen swaying of high-rise buildings.

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[jbengt]

Thus the ability to tune the resonant frequency against the waves using the air valves.

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[SirCowMan]

The volume of water will be on order of 2% of the vessels overall weight, so yes it will be a massive amount of weight. Most of the roll-dampening is provided by the hull's natural resistance to roll and the center of mass of the vessel typically being low. This system itself works not by moving the water per-se, but by controlling the natural roll of the water within the U-shaped tank to counteract that motion. By adjusting the air valves, the natural frequency of the tank can be modified (the response cur

SWATH doesn't require power

[CanadianRealist]

Small Waterplane Area Twin Hull (SWATH) [wikipedia.org] is a design that minimizes the effect of the waves. Most of the volume that supports the ship is below the level of the waves, making it very stable. The stability comes from the hull design, so it doesn't require any power and the stabilization isn't prone to failure like an active system.

Here's a short video [youtube.com] of a SWATH ship in rough seas, with a regular hull ship for comparison. I'm pretty sure this is the one that I saw in a documentary about the design. They showed a glass of water sitting on a table in the SWATH ship, not spilling. I'm pretty sure that the glass would go flying in the other ship.

Re:

[DerekLyons]

OTOH, SWATH hulls are more expensive than conventional hulls and offer less volume per displacement ton.

Re:

[SirCowMan]

SWATH's make nice boats. The tradeoff is in the narrow hulls down to the pontoons - it's limiting not only from a tankage perspective, but also in terms of arranging the driveline and providing sufficient access. They require a wide footprint to provide adequate stability, and like an oil rig, must be very carefully considered for safety when damaged.

Mercury Pots

[Lev13than]

Reminds me of the chapter in Neal Stephenson's The Confusion (part of The Baroque Cycle [wikipedia.org]). Japanese mercury vendors try to disable the Minerva (an armed merchant vessel) by filling its cargo hold with half-filled pots of mercury, rather than filling them to the brim. The idea is that the sloshing in the hull would resonate with the waves at the entrance to the harbour and slow the ship enough to be captured (or something to that effect). There's a discussion of whether Stephenson got the science correct here [blogspot.ca].

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[SirCowMan]

Rather than weights, gyroscopes are sometimes used.. the ship will be mostly still, there will still be a small bit of motion and if not done right the non-linear response of the dampened vessel can lead to sea-sickness. Also, it will still heave.

Those foolish fools!

[93 Escort Wagon]

Haven't they learned that the best way to survive is NOT to make waves?

Wow! Just like ...

[PPH]

... lots of high end yachts.

This has been done for a few years now. Fuel and potable water tanks in the ships sides connected via pipes with computer controlled valves. Some sailboats include pumps to actively move liquid to the windward side tanks to decrease heeling.

It's much older than that...

[DerekLyons]

More than just a few years now... try a few decades. (More like a century in fact.) They're called anti-roll tanks [wikipedia.org], and were first used around the turn of the 20th century.

(Naval architecture geek FTW!)

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[SirCowMan]

They certainly are used used today and practical, though the are also somewhat dangerous if not operated with due regard to their ability to increase a ships chance of capsize. In addition to the anti-roll tanks in the Wikipedia article, there are also 'heeling tanks' - large ballast tanks with oversized bilge pumps used primarily in icebreakers to rock them as they transit through ice, though they are not intended to offset a rolling motion. For a vessel where motion control is imperative, such as a resea

Re:

[SirCowMan]

In the old days, yes, fuel tanks would be afterwards filled with water and used as ballast, with obvious environmental consequence. There will be a bit of water in ships which use residual fuel, it goes through a seperator before use. Some modern vesssels still mix use fuel and ballast in the same tank to maintain a constant displacement, i.e., naval vessels, though where still done they are seperated by a rubber bladder inside the tank.

How to sink a ship.

[Anonymous Coward]

They had better get it right. When I use to drive a tractor/tanker, if you didn't get your 1st an 2nd gear shifting just right, the chemicals in the tank would shift with such extreme force, that it would almost knock your head off. You can easily hurt your back driving a tanker. I can just see a ship getting the wave out of sink and bursting a hold in the hull.

Not inner waves. Two actions at work.

[advid.net]

This isn't inner waves, but water moving back and forth in a U shaped tank (water is pushed by compressed air on the tops of the U shape, alternatively).
So there's no wave at all in the tank.

I just wonder:

Is the counter-reaction mainly cause by the counter-weight of the water which fills only one side of the U tank, or by the momentum (acceleration) given to the water rolling in the tank ?
In either case, it could be more easily done with some solid weight on rails, with less energy lost (air compression and fluid displacement).