USS Zumwalt DDG-1000 Launched

[Borgholio]

Therefore, if you try to arbitrarily decide what shape the ship will have, then ignorantly insist that all the needed systems be shoehorned into that shape somehow, you're going to get a poorly performing ship.

That's a good point, but it was the exact same way with the F-117. It's radical design made it so unstable, that it was very dangerous to fly without the help of the fly by wire system.

I expect future stealth ships to be a more conventional (stable) design.

[Simon_Jester]

The real problem is that the sea is a less... simple environment than the sky.

To a good first approximation, air exerts only two forces on an aircraft: lift that acts only on a pair of 'wings,' and drag. As long as you can come up with an acceptably curved and streamlined shape, the plane will fly reasonably well. Optimization takes effort, but it will work.

The sea exerts many more forces on a ship: wave action in all three dimensions, drag, buoyancy which has to be fully integrated over the volume of the ship rather than acting chiefly on a pair of 'wings,' plus weirdness caused by the way that moving parts of the ship create wakes in the water and have to exert great force to shove many tons of water out of the way as the ship moves.

Moreover, a ship has nothing like the range and flexibility of control surfaces enjoyed by an aircraft. An aircraft can be designed to "fly by wire" in such a way that the computer autocorrects any undesired motion in any direction, so that an inherently unstable plane rights itself before the pilot even notices the problem. Doing this on a ship is much harder and may even be impossible. Not because we don't know how to actively control the balance and orientation of a ship at sea, but because doing so for an object as large as DDX-1000 requires doing it fast, by shifting very large weights very considerable distances, not just twitching flight control surfaces.

Well behaved ship hulls all have to look more or less the same, whereas there are a LOT of different viable hullforms for an aircraft.

[Borgholio]

hmm...well we DO know that the Zumwalt class has ballast tanks that are used to stabilize the ship so it can get improved accuracy off of it's deck guns, I wonder if the same system is intended for use while the ship is underway to counteract rough seas?

[TimothyC]

hmm...well we DO know that the Zumwalt class has ballast tanks that are used to stabilize the ship so it can get improved accuracy off of it's deck guns, I wonder if the same system is intended for use while the ship is underway to counteract rough seas?

It is. It's also a platinum plated system that is needed because of the tumblehome hull and the wave-piercing bow. The problem is that this system is stable, without being steady - basically the ship is going to have a very short, very violent rolling motion (this is good in that it means she's not likely to turn turtle right away, but bad in that when she does roll, she's going to be throwing people and things around very hard - I wouldn't be surprised if they get a lot of bruised elbows on the ship.

[Simon_Jester]

This is a more precise way of explaining what I was getting at earlier.

On an airplane, a fly-by-wire system can easily deliver very small control inputs. The computer detects a 0.1 degree shift in the plane's orientation, it twitches the tail rudder a bit, and the plane is back on course. The pilot doesn't even notice, because small changes in the plane's motion can be triggered by slow, gentle motions.

On a ship, a sail-by-wire system will need to shift large masses of ballast very quickly to counteract wave action. So the ship gets hit by a wave- but there are tons and tons of ballast to move; you can't just gently twitch something and counteract the motion of a huge wave slamming into the side of your ship. So you get one short violent motion, followed a fraction of a second later by another short violent motion, as the ship's sail-by-wire system catches up to what's going on and moves the ballast.

It's a harder order of problem than fly-by-wire.

[Sea Skimmer]

That's a good point, but it was the exact same way with the F-117. It's radical design made it so unstable, that it was very dangerous to fly without the help of the fly by wire system.

I expect future stealth ships to be a more conventional (stable) design.

The F-117 is physically impossible to fly without the computer, to an almost comical degree. If the system fails you have IIRC either 20 or 30 seconds to eject before it will enter such a violent spin that a survivable ejection is no longer possible.Interestingly though as long as the computer does work, the very nature of its 3 axis instability means it has a wide margin to keep itself under control even if say, one of the tail fins falls off as happened on a test flight.

The stability issues with an aircraft vs a ship are not really comparable though, and adapting a more conventional hull inherently creates a corner reflector where the hull hits the waterline. You can't get around this. The Arleigh Burke and La Fayette classes pretty much represent the limit of what naval stealth can do without going to radical hullforms like Sea Shadow or DDG-1000.

As an aside, it remains interesting that the USN did not adapt active active stabilization for the class. This doesn't really help with stability in safety terms, but it ought to have improved stealth. The USN has never really liked the technology though, and might have been an issue with acoustical stealth, which is an underrated part of the DDG-1000 design. The whole ship has a pretty strong ASW focus.

[Sea Skimmer]

On a ship, a sail-by-wire system will need to shift large masses of ballast very quickly to counteract wave action. So the ship gets hit by a wave- but there are tons and tons of ballast to move; you can't just gently twitch something and counteract the motion of a huge wave slamming into the side of your ship. So you get one short violent motion, followed a fraction of a second later by another short violent motion, as the ship's sail-by-wire system catches up to what's going on and moves the ballast.

It's a harder order of problem than fly-by-wire.

Heavier, not harder. Anti rolling tanks are rather old technology and work fairly well without any active intervention by the ship other then to adjust the amount of water in the tanks if the ship changes displacement. Active stabilizer fins are fairly old too, though not century plus like rolling tanks.They can and have been made to work with purely electro mechanical controls, since all you need is a roll sensor. IIRC DDG-1000 has some kind of anti rolling tanks, but the question is how big are they vs sea state.

The situation is much simpler because the ships desired movement is purely two dimensional, and your stabilizing the ship in a different axis then the ones the crew want to control. The anti rolling system thus operates totally independently of the helm. Also water is more or less a static thing, since it doesn't meaningfully compress. So while an anti rolling system can exploit a wind or sea current sensor, it doesn't really need them to do its job properly.

On a plane meanwhile, most 'unstable' aircaft are actually only partly longitudinally unstable, but since pitch is a desired direction of control for the pilot it needs a constant interaction to work right. You could make that work mechanically, I think it was tried once or twice, but fundamentally it will never work well without a computer because air conditions vary so much and so many inputs need to be integrated in real time. Meanwhile on an F-117 you had all three axis highly unstable, which is nightmarish.

Anyway on DDG-1000 the model trials suggest the helicopter deck will almost be underwater in a high speed turn, apparently that was just accepted for the victory of freedom; but the killer concern if is the ship takes serious flooding damage. To a point this should not matter stability wise, because the ship has no longitudinal bulkheads, but the tumblehome does mean the lower the ship sinks, the faster it sinks. If the hull flares out your sinking rate (for a fixed intake of water) goes down as you sink because the hull is wider and needs more water to flood. No way exists to get around that without changing hull form, or adapting some batshit insane idea I might dream up, like a giant lifejacket for the ship that inflates on demand with 300ft long kevlar balloons.

Oh also the ship will take water over the bow like crazy, but that was the entire point of a 'wave piercing bow' which did indeed work very well in model trials for its desired reduction of the ships wake. It remains to be seen if this is going to scale up, but model trials are decently accurate for that sort of thing.

It is. It's also a platinum plated system that is needed because of the tumblehome hull and the wave-piercing bow. The problem is that this system is stable, without being steady - basically the ship is going to have a very short, very violent rolling motion (this is good in that it means she's not likely to turn turtle right away, but bad in that when she does roll, she's going to be throwing people and things around very hard - I wouldn't be surprised if they get a lot of bruised elbows on the ship.

Hockey pads for every man and women onboard; just think how much money the low manning design will save us on issuing these!

[Simon_Jester]

I simultaneously hope there will, and will not, be humorous anecdotes about how ten tons of seawater get into the interior spaces because someone forgot to close a hatch properly before the ship started moving at speeds where it practically turns into a submarine.

As to the difficulty of roll control- I guess what I'm getting at is that it seems harder to control the roll of the ship in a way that is "consequence-free" for the end user. Once your fly-by-wire system works, even if your aircraft is unstable it still flies properly. Here, the sail-by-wire system more or less works, but it has real consequences (a very rapid, abrupt roll with high accelerations and high jerk).

[Patroklos]

The Burkes can take blue water over the flight deck at high speeds too.

[LaCroix]

The Burkes can take blue water over the flight deck at high speeds too.

Theres a slight difference between "will take occasional blue water over the deck at high speeds and rought sea" and "blue water over the deck expected whenever it moves faster than a rowboat"...

[Patroklos]

Thats not what is expected, but rather at high speeds and turns. There is nothing wrong with this as long as its known and designed around it. You don't land helos in high seas anyway so as long as its water tight and corrosion control is addressed its no big deal just like its not with the bow.

[Crayz9000]

Pretty much all ships run on unix based operating systems, along with almost all servers and industrial, research and defence supercomputers.

Wrong. Wast majority of computers on ship are embedded industrial systems. These run on whatever embedded OS producer orders - things like RISC OS, LynxOS, ThreadX, or (surprise!) Windows CE. None of them are based on Unix, at best some are unix-likes, but with different kernels and architectures. Why would they be? These are not desktops.

In this case, the Combat Information Center's master control setup is running a mix of LynxOS (for the actual control modules) and Linux (for the graphical interface). There's a cluster of Linux servers in a containerized module inside the ship which presumably provides the virtual machines used in the CIC control stations.

[Captain Seafort]

Ah, and here I thought you were sticking up for the Swedes.

Nah, I was making a joke about how it was time for the USA to take one for the archeologists. Every other nation has obliged us....

Doesn't the Monitor count?

[Borgholio]

Doesn't the Monitor count?

The Monitor-class ships were definitely not meant to operate in heavy seas or far away from the cost. But given how they were the very first turreted ships in history and the first ironclads ever built by the US Navy, I'd say that the fact the Monitor was lost in a storm was due to lack of experience with that kind of ship.

I don't think it would count in the same class as the Vasa, which was overconfidence and pushing the limits of what was already known to be stable just to make the King happy.

[Thanas]

Ah, and here I thought you were sticking up for the Swedes.

Nah, I was making a joke about how it was time for the USA to take one for the archeologists. Every other nation has obliged us....

Doesn't the Monitor count?

No as it was not one of the largest ships at the time of the sinking and her loss was insignificant.

[Sea Skimmer]

I simultaneously hope there will, and will not, be humorous anecdotes about how ten tons of seawater get into the interior spaces because someone forgot to close a hatch properly before the ship started moving at speeds where it practically turns into a submarine.

I'd worry more about what happens normally when green water breaks over the gun turrets. Better hope those suckers have one heck of a good seal on the turret ring.

As to the difficulty of roll control- I guess what I'm getting at is that it seems harder to control the roll of the ship in a way that is "consequence-free" for the end user. Once your fly-by-wire system works, even if your aircraft is unstable it still flies properly. Here, the sail-by-wire system more or less works, but it has real consequences (a very rapid, abrupt roll with high accelerations and high jerk).

That need not be the case, both active stabilization and anti rolling tanks can be adjusted if desired, though your options for adjusting the anti rolling tanks are slower and less effective as all you can do is vary the amount of water in them and open or close valves. Most designs didn't really intend for that to be done, but it can be if desired. Active stabilization can make a ship barely roll at all, which is the reason why cruise liners with such massive superstructures are practicable vessels, most of the time. When the stabilizers fail you get those great videos of the passengers and furniture being thrown beam to beam. This is actually a big contrast to a ship relying totally on its innate stability, which is indeed subject to very real consequences you can't really do anything to change other then pumping on more ballast, assuming you have empty fuel tanks to do so in.

Fly by wire does just work, but because its always active the pilot isn't noticing the fact that his plane has increased drag and corresponding loss of speed, acceleration and range. On the F-117 the unusual shape and fly by wire demands worked out to be around a 20% increase in drag compared to a conventional plane of the same size and power.

The Monitor-class ships were definitely not meant to operate in heavy seas or far away from the cost. But given how they were the very first turreted ships in history and the first ironclads ever built by the US Navy, I'd say that the fact the Monitor was lost in a storm was due to lack of experience with that kind of ship.

It was a calculated risk too. The USN was blatantly aware its cheesebox on a raft built in 100 days was not seaworthy, but the Confederates were fast completing not one but two ironclads at Charleston harbor and the blockading squadron was even weaker on average then the frigates Virginia had shot to pieces. Its also not like good weather forecasting existed.

As it worked out, those Confederate ironclads did then sortie and forced one blockade steamer to surrender, heavily damaged another in IIRC Jan 1863, but because the squadron was in open water the remaining ships were able to retreat out of reach of the Confederate and maintain the blockade. However it was much looser as a result and a larger number of blockade runners could then slip past it.

[The_Saint]

So how long until Sea Wraith sees the light of day?

Is there any idea whether Sea Wraith would look the same as Zumwalt below the waterline?

[Sea Skimmer]

Never? Sea Wraith was a 90s company concept updated in the 2000s and then dropped, such concepts are rather numerous. The only serious plan for a new UK surface combattant is the Type 26 Frigate which has an entirely conventional hull and superstructure signature reduction work comparable to that of the Arleigh Burke or La Fayette, not any radical attempt at wave piercing submarine bow stealth.