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Stealthy  Ships
Improving Ship Stealth using Sea Water Curtain
------Main Page---Details, Technology---Links---FAQs---Glossary----
SUMMARY
Proposed is a technology (AWCT) for adding Stealth properties to existing U.S. Fleet surface ships by the use of sprayed sea water.

The Adaptive Water Curtain Technology (AWCT) is intended to deflect and scatter enemy radar waves thus reducing the ship’s radar cross section (RCS). It consists of (highly conductive) sea water sprayed in a fashion that effectively creates an angled radar reflective curtain around the ship.

To reduce the ship’s remaining RCS, the water curtain can be "modulated" such that the returns appear as "Sea Clutter." This could be done by determining the surrounding Sea State--either locally, or from satellite Sea State data, i.e., deriving the Sea Clutter Spectrum; and applying the appropriate coefficients to the modulating process for optimum mimicry.

This approach is suggested as an "Add-On" to existing surface ships, an interim measure until the next generation DD(X) of stealthy surface ships has replaced this class. The Arleigh Burke class Destroyer--which has rudimentary stealth technology, is used as an example of a recipient ship for this technology. Although this class of ship has a reduced RCS over its predecessor, it can still benefit significantly from the proposed technology. 

This technology can reduce a surface ship's vulerability to Radar cross-section (RCS), Infrared signature (IR), and Visual signature.

This is a Work in Progress.
There are fundimental questions yet to be answered.   See List

 -
  FEATURES:

  1)_ Reduced RCS.

  2)_ IR Signature Mitigation of Ship Stacks by the use of "Pre-Cooled" Water Curtain. 

  3)_ Reduced Visual Signature (Camouflage).

  4)_ Possible EMP Protection.     more

  5)_ System able to mimic Sea Clutter.

  6)_ Water streams can be "Modulated" for enhanced concealment. 

  7)_ Uses Fire Fighting Technology.

  8)_ Compensation for finite Water Stream boundaries (gaps), using Spray and Misting.

  9)_ System uses Feedback for accurate positioning of Water Stream "Landing zone."

10)_ Able to (actively) Resist Wind Loading on Water Curtain.

11)_ Can Selectively open Gaps in Water Curtain for Radar, IR, Communications, etc.

12)_ Satellite (or RPV) for Interactive Sensing and Alignment for Stealth Optimization. 

13)_ System Cleaning by Periodic Flushing with brackish or clean water.

 

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-The Sea Shadow, Stealthy Ship Testbed-

-Sea Shadow, sporting 45º angle Faceted, Radar Reflecting/Absorbing, Hull-
 
-USS Zumwalt (DD-21)-

DD(X) Class Stealthy Multimission Destroyer, 
----------construction starting in 2005; comissioning expected ~ 2008--- more info
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-Radar Evasion by Shaped Water Curtain-

----------Full Water Curtain---------------DDG-67-------------Stepped/Folded (Fresnel lens)
The Adaptive Water Curtain Technology (AWCT) is intended to deflect and scatter enemy radar waves thus reducing the ship’s radar cross section (RCS). It consists of highly conductive sea water sprayed in a fashion that effectively creates an angled radar reflective curtain around the ship.
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-Fire Fighting Technology used in AWCT-
Fire Boat projects high pressure water streams hundreds of feet into the air 
using powerful Diesel water pumps feeding steerable nozzles called Monitors.-
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-Active Water Curtain Technology-

Array of Powerful Water Pump outlets creating Water Curtain-
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-Water Curtain Modulation-
Nozzle Control for 'Sea State' Mimicry
To reduce the ship’s remaining RCS, the water curtain can be "modulated" such that the returns appear as "Sea Clutter." This is done by determining the surrounding Sea State--either locally, or from satellite Sea State data, i.e., deriving the Sea Clutter Spectrum and applying the appropriate coefficients to the modulating process for optimum mimicry.
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 -Directable Fire Fighting Water Jet known as a "Monitor"-

Note Hydraulic Actuators for Automated Controls, including 
Azimuth, Elevation, Pressure, Spread, Modulation, etc.-
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-Water Pump-

Water Jet Propulsion Pump.
Powered by Jet Aircraft Engine
One Aegis Class Cruiser would require ~ 20 such 
pumps for approximately 200,000 GPM water flow-
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-Arleigh Burke DDG-51 using some Shaped Water Curtains-

Click image for larger version    188 kB-
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-‘Tweaking’ for Optimum Stealth, using Satellite or UAV-
Optimizing Mimicry, Interactively-
Satellite Sea State Data could either be taken from the NOAA database, or for better accuracy,  certain DoD satellites could be tasked to directly observe the ship’s unique signature in real-time,  while interactively ‘tweaking’ for optimum stealth. There could also be a locally launched UAV to do this same interactive alignment.
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-Idealized Examples: AWCT Hiding All, including Superstructure-

 Water Pressure and Nozzle Angle Shape and Control Coverage, 
Note: this type of coverage also helps Mask the Stacks' IR Signature  -
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-Without AWCT, 7° Roll Exposes Starboard Side to Radar-

AWCT Holds Form despite Roll-
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-Active Windowing,
Rapid Modulation of Pump Nozzles-

Creating Dynamic Openings in the Water Curtain 
Useful when synchronized with Radar and other Sensors -
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-Adaptive Selective Opening of AWCT,
"Peeking Out"-

Synchronized Openings for Radar, Sensors, etc -
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-EMP Defense?-

Conductive Sea Water Shunts EMP currents to 'Ground' 
Super Saturated Salt Water added for enhanced conductivity
More on EMP -
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-Water Inlet-

Water Inlet at Bow for "Ram Boost"-
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-Water Inlet-

Water Inlet incorporated into new "Bulbous Bow"-
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------Main Page---Details, Technology---Links---FAQs----
Partial List of Anti-Ship Cruise Missiles (ASCM)   more info
USA
AGM-84 Harpoon / Harpoon Block II

France
Exocet AM39 / SM39 / MM40 / BC40
AS 15 TT

India/Russia
Brahmos (PJ10)

Russia
SS-N-27 Klub
SS-N-25 Switchblade
SS-N-22 Sunburn
SS-N-19 Shipwreck

China
C-701

Germany
AS.34 Kormoran 1/2

EU
Polyphem

Norway
Penguin
NSM

Britain
Sea Skua

Sweden
RBS 15 Mk3

Italy
Otomat Mk2

Israel
Gabriel III
 

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   LINKS:
       Glossary, Ship

       Glossary, Radar

       Glossary, SARadar

       Beaufort Scale, Sea State

       Bulbous Bow Technology

       Anti-Ship Cruise Missiles

       Sea Shadow
 

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       -FAQ-
1)_ Q... What makes water able to fend off  RADAR detectionIR Detection?

       A... Water, especially sea water, is highly electrically conductive and if the water droplets are compact enough, RADAR waves will be reflected just as if the surface were metal.  Also, streams of sea water will absorb as well scatter radar energy. 
         ... Heat from the stacks, etc., can be obscured from IR Detection by sufficiently thick Pre-Cooled water blanket.


2)_ Q.... What is Sea Clutter?

       A... Radar backscatter from an ocean surface is commonly referred to as Sea Clutter. 
Any radar backscatter not due to the scattering from an ocean surface constitutes a potential target.  more info


3)_ Q.... Won’t enemy RADARs with MTI detect the water curtain’s motion?

       A... The water curtain is a surface of fast moving water droplets forming random patterns and movements mimicking the surface motion of the sea water surrounding the ship--Sea Clutter.   See 2)_


4)_ Q.... In addition to RADAR, IR, INS, GPS, Terminal Guidance, etc., Anti-Ship Missiles (ASM) uses a Radio Altimeter which will maintain it at about 3 meters above wave tops; so, once launched toward the ship, what’s to prevent the missile from "blindly" slamming into the side of the ship? 

       A... If the ASM is launched close in, and the target ship does not move out of the way, the missile will either detonate upon contact, or resort to "salvage fusing" (Salvage Detonation).


5)_ Q.... If the water intake is at the bow, taking in thousands of GPM, how will that effect the ship? 

       A... It may relieve the bow wave pressure which would improve speed and range; or NOT.


6)_ Q.... What happens when the wind blows the water curtain?

       A...The system is adaptive, that is, it monitors each ‘water stream landing zone,’ and by adjusting the appropriate nozzle/monitor/pump combination (including azimuth, elevation, water pressure, spread, modulation, pulsing, etc.), compensates for wind speed and direction (wind loading). 


7)_ Q.... How does it know where the ‘water stream landing zone’ is?

       A... Each nozzle is electrically isolated such that a multiplexed low frequency signal is applied to the water stream (via the nozzle); at the water stream landing zones there are arrays of antennas that "look" for the temporal electrical signal. The antennas are spatially sensitive allowing for water stream error detection and correction.


6)_ Q.... How will the corrections be made? 

       A... The nozzle/monitor/pump combination allows just about any correction to the water streams.


7)_ Q.... Will the water curtain need to be active all the time?

       A... Probably not, during obvious threats and times of uncertainly it might be fully active; otherwise, the more vulnerable (large RCS) areas of the ship might be active 24/7.


8)_ Q.... What damage--if any--will result of spraying sea water on the ship’s outside?

       A... It isn't clear if this extra salt water will add to the maintenance of the vessel; however, the use of Fresh Water could be used, periodically (e.g., at shut down), to wash-down the affected areas.


9)_ Q.... Won’t the water curtain block or interfere with the ship’s Radars, radios, sensors, etc.?

       A... It could, however, any and all EW operations with the "outside world" would be coordinated with the AWCT.   see peeking out


10)_ Q.... How can the water curtain "peek holes" be synchronized with all of operating EW equipment?

       A... See 9)_ above.


11)_ Q....What will be the impact of running pumps, falling (spent) water, etc., on the ship’s sonar siginature

       A... That is a question yet to be answered.


12)_ Q.... Are there "angles-on-the-ship" that are more vulnerable to detection than others, e.g., like the bow?

       A... Depending on the ship's speed and the relative wind direction, etc., the bow could be the most vulnerable. Of course, during a storm the sea state will aid the ship in its stealth.


13)_ Q.... What is "Radar Cross Section"?

       A... The radar cross section (RCS) of a target is the projected area that would intercept the transmitted signal and reflect isotropically an amount that produces the returned signal at the receiver. In other words, radar cross section provides an indication of how well a given target reflects radar energy.       more info


13)_ Q.... What is "Bragg Scattering"?

       A... Bragg Scattering is the enhanced backscatter due to coherent combinations of signals reflected from a rough [sea] surface having features, with periodic distribution in the direction of wave propagation, and whose spacing is equal to half of the wavelength of the incident radar waves as projected onto the surface. This is most easily detected by HF radar.
 

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Fundamental questions to be answered:
1)_ Wind Effects: wind loading on solid stream, tables, and/or plots.

2)_ Radar properties of sea water, solid stream, breaking stream, spray, misting: absorption, scattering, refraction, and reflection. 

3)_ The effect of 'pre-cooled' water curtain on IR signature of exhaust stacks. 

4)_ Effect of falling water (from water curtain) on ship's acoustic signature.

5)_ Maximum (GPM) amount of water required for optimum effectiveness.

6)_ Features required for optimum mimicry of local sea state, i.e., boundary between water curtain and sea surface..

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misc notes:
 false-alarm rates

With these ideas in mind, it is not surprising that the physical area of a target is normally greater than the radar cross section because some the incident energy is scattered and absorbed by the target. Use of radar absorbent material (RAM) and specific shapes and angles helps to minimise the radar cross section. Target aspect also changes the radar cross section markedly and needs to be allowed for in the design of a radar system. Radar designers normally use extremely pessimistic (low) values for radar cross section during radar design and performance calculations to ensure their systems meet minimum requirements when introduced into service.

The radar cross section of a target is not constant with operating frequency. There are three broad areas of interest with respect to physical target size, operating frequency and resulting radar cross section. These areas are:
 

Proposed is a technology for adding Stealth properties to existing U.S. Fleet surface ships by using an "Active Curtain" of conductive sea water.

The Adaptive Water Curtain creates Virtual Faceted Surfaces.

One of the greatest threats to surface ships is the sea-skimming Anti-Ship Cruise Missile (ASCM), which is a "fire and forget" supersonic radar guided missile; Exocet and Harpoon being the better known. 

To combat this threat, Stealth Technology is being incorporated in the newer ship designs.

 The Active Water Curtain Technology (AWCT) is meant for use on existing ships not already having stealth qualities; as well as an adjunct to existing stealthy ships. 

My motivation for researching and creating this web page on this subject  is the same as for my  page: a wish to contribute to the 'common defense' of this great nation.

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