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A stealth ship is a type of ship which is especially used as a war vessel and is concealed from the navy vessels of other countries. It is an important warfare tactic that is used by nations wide across the world. Since they are invisible but the opposite navy vessels are not, it gives a very big boost and advantage to the stealth ships to successfully launch an attack.
The main detectors that find out whether a navy vessel of an enemy country is in the oceanic water are the SONAR, the radar and the Infrared. Stealth ships are designed in such a way that they are harder to detect by one or more of radar, visual, sonar, and infrared methods and other detection methods.
These techniques borrow from stealth aircraft technology, although some aspects such as wake and acoustic signature reduction (acoustic quieting) are unique to stealth ships’ design. Though radar cross-section (RCS) reduction is a fairly new concept many other forms of masking a ship have existed for centuries or even millennia.
Ship Stealth Technology
Visual Camouflage
Visual camouflage is probably the oldest form of stealth, with records going back almost as far as the writing of ancient mariners using visual tricks to make their ships harder to spot. Though still relevant this area has taken on lesser importance with the advent of long-range radar.
Shaping
In designing a ship with reduced radar signature, the main concerns are radar beams originating near or slightly above the horizon (as seen from the ship) coming from distant patrol aircraft, other ships or sea-skimming anti-ship missiles with active radar seekers. Therefore, the shape of the ship avoids vertical surfaces, which would perfectly reflect any such beams directly back to the emitter. Retro-reflective right angles are eliminated to avoid causing the cat’s eye effect.
A stealthy ship shape can be achieved by constructing the hull and superstructure with a series of slightly protruding and retruding surfaces. Furthermore, round shapes on the ship are eliminated or covered up, examples include smokestacks and gun turrets. Also, cavities that present a horizontal face are to be eliminated since they act like a trap and are very visible to radar. To get around these limitations many ships use features such as panels that cover reflective surfaces or use alternate designs of hardware.
Also, every effort must be made to have the smallest gaps on the ship as possible. Hull shapes include tumblehome hull designs that slope inward from the waterline, and small-waterplane-area twin hulls (SWATH) which allow for better stability when using a tumblehome hull. These RCS design principles were developed by several navies independently in the 1980s using work done on aircraft RCS reduction as the starting point.
Signature reduction
Stealth technology represents more than just a low RCS; noise reduction plays a huge role in naval stealth because sound travels much better in water than air. Some of the techniques used include muffled exhaust systems, modified propeller shapes, and pump-jets. The shape of the hull can also have a great effect on the reduction of the noise from a ship. Another major element is signal emission control. Modern warships emit much electromagnetic radiation in the form of radar, radio, and even bleed-off from the ship’s electrical systems. All of this can be used to track a ship and thus modern stealth ships often have a mode that switches off many of the electronic emissions, the downside of course is that the ship then has to rely on passive sensors and can’t easily send messages further than line of sight.
Also of great importance are thermal emissions. A heat signature can make a ship stand out like a candle in a dark ocean making it easier to spot and because it is possible to see infrared emissions through features that would normally hide a ship such as fog, or a smoke screen, many detection platforms like patrol aircraft, UAV’s, and satellites often have the ability to see multiple bands in the infrared spectrum including heat. This necessitates the control of these emissions. The most common way is to mix any hot gasses emitted by the main source of heat which is the engine’s exhaust with cold air to dilute the signature and make it harder to pick out the ship from the background warmth. Another method vents the exhaust into the water though this increases the ship’s acoustic signature. For the hull water can be actively distributed across the hull of the ship cooling the ship.
Acoustic Signature
Ships have acoustic signature, a combination of acoustic emissions of sound emitters, made up of a number of individual elements. These include:
Machinery noise: noise generated by a ship’s engines, propeller shafts, fuel pumps, air conditioning systems, etc.
Cavitation noise: noise generated by the creation of gas bubbles by the turning of a ship’s propellers.
Hydrodynamic noise: noise generated by the movement of water displaced by the hull of a moving vessel.
These emissions depend on a hull’s dimensions, the installed machinery and ship’s displacement. Therefore, different ship classes will have different combinations of acoustic signals that together form a unique signature
Warship designers aim to reduce the acoustic signature of ships and submarines just as much as they aim to reduce the radar cross sections and infra-red signals. The acoustic signature can be reduced by
fitting of machinery with the best possible mechanical tolerances and designed to produce a minimum of noise.
decoupling the machinery from the hull by mounting machinery on rubber mounting blocks.
designing propellers to reduce cavitation, this led to the development of large slow turning propellers, today there is a preference now for pump-jet propulsors over propellers.
the fitting of anechoic tiles to the hull, however ill fitting and loose anechoic tiles can themselves be a source of noise.
hydrodynamic efficiency to minimise the perturbation of water.
care in minimising protrusions from the hull.
Materials
Just like choices in shaping, the choice of materials affects the RCS of a ship. Composites such as fiberglass and carbon fiber are great blockers of radar and give smaller vessels an advantage in further RCS reductions. However, composites are fragile and often unsuited to larger ships or ships that expect to take fire, though new laminates can partially negate some of the weaknesses. This restricts larger ships to metals such as steel and aluminum alloys. To compensate a ship may include a coating of a radar absorbing material though this can be quite expensive and may not stand up to the corrosive effects of salt water.
Stealthy Ships
The technology for the stealth ship was first developed and used by the German navy. Over the years almost every country has adopted the technology quite successfully. At present, the Swedish navy is known to be the best designer of such navy vessels. Some of the other navy vessels that operate as stealth ships are the British Type 45, Germany’s Braunschweig Corvettes, India’s Shivalik range of ships and China’s Houbei missile boat. The stealth technology used in these ships needs to be constantly updated for navies of countries around the world keep on updating their combating technology continuously.
The currently developed U.S. Zumwalt-class destroyer — or DD(X) — is the US version of a stealth ship. Despite being 40% larger than an Arleigh Burke-class destroyer the radar signature is more akin to a fishing boat, according to a spokesman for Naval Sea Systems Command sound levels are compared to the Los Angeles-class submarines. The tumblehome hull reduces radar return and the composite material deckhouse also has a low radar return. Water sleeting along the sides, along with passive cool air induction in the mack reduces infrared signature. Overall, the destroyer’s angular build makes it “50 times harder to spot on radar than an ordinary destroyer.
The Swedish Navy’s Visby class corvette is designed to elude visual detection, radar detection, acoustic detection, and infrared detection. The hull material is a sandwich construction comprising a PVC core with a carbon fibre and vinyl laminate. Avoidance of right angles in the design results in a smaller radar signature, reducing the ship’s detection range.
Britain’s Type 45 anti-air warfare destroyer has similarities to the Visby class, but is much more conventional, employing traditional steel instead of carbon fiber. Like Visby, its design reduces the use of right angles.
Taiwan’s’ Tuo Chiang-class stealth corvette are a class of fast stealth multi-mission corvettes currently in service with the Republic of China (Taiwan) Navy. The ships is designed to have a low radar cross-section and evade radar detection making it difficult to detect the ship when operating closer to the coastline.
Russia is building its first naval ship that will be fully equipped with stealth technology to make it hard to detect, the RIA state news agency reported in June 2021. The hull of the Mercury naval corvette dubbed project 20386 has already been built and the vessel is expected to be delivered to the navy next year, RIA reported, citing two unnamed sources in the shipbuilding industry. The warship will be armed with cruise missiles, anti-aircraft missiles and artillery, as well as being capable of searching for and destroying submarines, RIA said.
Russia has incorporated stealth technology such as a radar-absorbing coating into some of its navy vessels, but those ships have not had full stealth technology, RIA said. The Mercury vessel will have a radar-absorbing coating and a special shape to minimise protrusions and crevices on its surface, RIA said. It is also expected to use composite materials and special paint.
