Why there are no "curved" stealth ships?

[X-39]

Forgive me if this question sounds dumb, but does basically every "stealthy" and LO vessel in service these days uses faceted designs? The first stealth ship, the IX-529 Sea Shadow,was born around the same time as the F-117 Nighthawk, so it's understandable that limitations in computational power were a reason they looked similar. But decades later current and future planned warships still retain that angular appearance instead of adopting the design philosophy of modern stealth aircraft. What's stopping the USN (or any other) from building a "B-2 Spirit of the Seas"? Some of my thoughts on why this might be unviable:

1-Less space and other limitations: Boxy designs give the most amount of space available, a sinusoidal profile would restrict even more volume available to the ship's internals.
2- Signature reduction on ships is not that worthy compared to aircraft, so using a careted simpler design might be more convenient if it works well enough. plus any kind of sensors bolted on the exterior will ruin your precious RCS like what happened to the Zumwalt.
3- A ship, unlike aircraft, can't remain in radio silence for too long, even less if it's part of a CSG.
4-Speed, ships are low and can be tracked by satellites, if you incease your sped, you also make the wake bigger, so that's a disadvantage, plus additional noise.


So far, the only concept I've seen of a curved stealth ship is the Ghost Fleet MUSV:

 

[stealthflanker]

Or that it can afford a large flat surface to make the lobes from the strongest specular smaller. The reason curving was done in the first place is to break down possible strong lobes where large, flat and angled surface cannot really be used.

Another additional reason is manufacturing as curving a large plates as one in ship might not as easy or economical as one in aircraft.

This is an example on Flat plating's work in reducing ship signatures into fractions of conventional ship. back in the day i model myself my own stealth attack craft. This was done in X-band (8 GHz). I call her Lanceria class. It may look curved in the image but it's because the 3D software's rendering (smooth shading made her so)



The RCS modeling

As one might see notice the strongest lobes are directed to upward of the ship. Also the size of the lobe, which are small. Comparison with conventional missile boat yield considerable differences both numerical and in terms of where the lobes are going. Where conventional missile boat have about Median of 740 sqm, while the treated stealthy missile boat can have as low as 14 sqm.

The lower image depicts the lobes between stealth treated vs conventional.

Will such reduction works ? Yes considering that maritime surveillance radar have to also contend with sea clutter which can have much larger RCS. Paired with the fact that there is a function between Improvement factors resulted from MTI or other form of processing vs speed. The ship can be at least in theory be moving in the "window" where enemy radar's improvement factor are the lowest. Thus making the ship being passed/filtered out as waves.



Above is example on Improvement factor of processing Vs target velocity. Notice that slow target and target at certain velocities are in the "window" where the improvement factor are the smallest. That would present difficulty in filtering the clutter away.

 

[Hobbes]

- ease of manufacturing.
- in an aircraft, curved shapes can give an aerodynamic advantage. In ships, that doesn't matter.

 

[starviking]

- ease of manufacturing.
- in an aircraft, curved shapes can give an aerodynamic advantage. In ships, that doesn't matter.

Possibly hull-strength issues too.

 

[Hobbes]

Generally, curved plates are stronger than flat plates. But it'd be a huge pain in the ass to have to run each plate through a rolling mill before assembly.

 

[TomS]

Generally, curved plates are stronger than flat plates. But it'd be a huge pain in the ass to have to run each plate through a rolling mill before assembly.

Plus, stealth shapes cannot be simple constant radius curves. So fabrication is even more difficult. Not to mention building the framing under the curve...

 

[Silencer1]

Generally, curved plates are stronger than flat plates. But it'd be a huge pain in the ass to have to run each plate through a rolling mill before assembly.

Then ships could be cast from light alloys in single piece!
P.S. Submarine should be cast from crud iron, for withstand deep pressure

 

[Bounce]

Now I wanna see someone 3D model an F-117 but round off all the angular edges.

 

[martinbayer]

Now I wanna see someone 3D model an F-117 but round off all the angular edges.

Assemble a model kit and do just that with a file and sandpaper .

 

[Nicknick]

According to my knowledge, the plates are very thick and partially hardend (on the outside, while beeing elastic on the inside). It might be very difficult to be bend them, weld them and harden the outer surface when they are curved.

What is the advantage of curved plates for ships?

 

[martinbayer]

Hydrodynamics comes to mind.

 

[Nicknick]

Yes, but the resitance is almost comletly dependant on the hull, not on the upper part which only causes some air resistance. Water is 1000 times denser than air.

 

[martinbayer]

Yes, but the resitance is almost comletly dependant on the hull, not on the upper part which only causes some air resistance. Water is 1000 times denser than air.

I understood the "curved plates" comment to apply to the ship as a whole, since a lot of vessels such as freighters and tankers already have boxy/(rect)angular superstructures anyway.

 

[TomS]

According to my knowledge, the plates are very thick and partially hardend (on the outside, while beeing elastic on the inside). It might be very difficult to be bend them, weld them and harden the outer surface when they are curved.

What is the advantage of curved plates for ships?

You're thinking about armor plate. Hull plating and modern superstructure skins are not generally (ever?) face hardened.

Curved shapes are used where required for hydrodynamics, but they are much more expensive than flat plates. And complex curves are more expensive than simple ones. So designers try to minimize the use of complex curves in shipbuilding wherever possible.

Aircraft want to use curved surfaces for better aerodynamics compared to flat plates and sharp edges. As you suggest, surface ships don't need that minor aerodynamic advantage, so there's no great incentive to use curved stealthy shapes.

 

[Nicknick]

basically, the same as I said...

 

[edwest4]

There can be curved ships. Difficult construction features don't mean anything if a weak or zero radar return is the result. See the book From Rainbow to Gusto by Paul Suhler to get a perspective regarding RCS.

 

[X-39]

@Hobbes @TomS I thought that differences in appearance between the F-117 and later aircraft can't be solely attributed to the need of better aerodynamics, the shaping also plays a role in how radar interact? Flat faces deflect incoming emissions into specific directions, while the B-2 case and UCAVs with similar construction achieve a different solution by making them ride over the smooth, unbroken bodies like a wave?

 

[X-39]

Now I wanna see someone 3D model an F-117 but round off all the angular edges.

I wouldn't be surprised if the result was something like this: