Acoustic signature is used to describe a combination of acoustic emissions of ships and submarines.

Contributing factors

The acoustic signature is made up of a number of individual elements. These include:

• Machinery noise: noise generated by a ships 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. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure A propeller is essentially a type of fan which transmits power by converting Rotational motion into Thrust for propulsion of a vehicle such as an
• Hydrodynamic noise: noise generated by the movement of water displaced by the hull of a moving vessel. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion

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. A ship class is a group of ships of a similar design This is distinct from a ship-type which might reflect a similarity of tonnage or intended use

Targeting

Hydrophones and Sonar operating in passive mode can detect acoustic signals radiated by otherwise invisible submarines, and use these signals to target attacks. A hydrophone (Greek "hydro" = "water" and "phone" = "sound" is a Microphone designed to be used underwater for recording or listening Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate

Modern naval mines and torpedoes such as the CAPTOR mine can be programmed to distinguish the acoustic signatures of different vessels, leaving friendly vessels unmolested and attacking high value targets when faced with multiple possible targets, e. A naval mine is a self-contained Explosive device placed in water to destroy Ships or Submarines Unlike Depth charges mines are deposited The modern torpedo (historically called an automotive automobile locomotive or fish torpedo is a self-propelled explosive Projectile weapon launched above or below The CAPTOR is the United States Navy 's primary anti-submarine Naval mine. High Value Target ( HVT) is United States Military terminology for a target (a person or resource that an enemy commander requires for successful completion g. distinguishing an aircraft carrier from its escorts.

Countermeasures

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. A countermeasure is a system (usually for a Military application designed to prevent Sensor -based Weapons from acquiring and/or destroying a target Radar cross section (RCS is a measure of how detectable an object is with a Radar. For submarines, as a prime factor in how they can be detected the reduction of the acoustic signature is a primary goal.

The acoustic signature can be reduced by

• fitting of machinery with the best possible mechanical tolerances and designed to produce a minimum of noise. Engineering tolerance is the permissible limit of variation in a physical Dimension, a measured value or Physical property of a
• decoupling the machinery from the hull by mounting machinery on rubber mounting blocks.
• designing propellers to reduce cavitation, there is a preference now for pump-jet propulsors over propellers. A propeller is essentially a type of fan which transmits power by converting Rotational motion into Thrust for propulsion of a vehicle such as an A pump-jet or water jet is a marine system that creates a jet of Water for propulsion. A propulsor is a mechanical device that gives propulsion The word is commonly used in the marine vernacular and implies a mechanical assembly that is more complicated than a
• the fitting of anechoic tiles to the hull, however ill fitting and loose anechoic tiles can themselves be a source of noise. Anechoic tiles are Rubber or Sorbothane -like tiles containing thousands of tiny voids applied to the outer hulls of military ships and Submarines as well
• hydrodynamic efficiency to minimise the perturbation of water.
• care in minimising protrusions from the hull.

Trimaran warships

For a time the Royal Navy toyed with the idea of the trimaran hulled Future Surface Combatant. The Royal Navy of the United Kingdom is the oldest of the British armed services (and is therefore known as the Senior Service) A trimaran is a Multihulled Boat consisting of a main hull ( vaka) and two smaller Outrigger hulls ( amas) attached The Future Surface Combatant is a Royal Navy programme to replace Britain's Type 23 frigates and a variety of smaller escort/patrol ships These would have had a very low acoustic signature. With three blade like hulls these ships would have cut through the water with a minimum of hydrodynamic noise. Radiated mechanical noise would also be minimised by using propulsors powered by a diesel-electric power plant; with the diesels being placed in the superstructure to mechanically isolate them from the water. A propulsor is a mechanical device that gives propulsion The word is commonly used in the marine vernacular and implies a mechanical assembly that is more complicated than a A number of vehicles use a diesel-electric Powertrain for providing locomotion. This project got as far as the construction of the research ship RV Triton to test the principle of a large scale trimaran design. Service with DERA and QinetiQ The Triton was designed as a demonstrator to prove that the trimaran concept would work successfully in a large warship

See also

• Underwater acoustics
• Stealth ship
• Type 45 destroyer
• Anti-submarine warfare
• Submarine warfare
• Upholder/Victoria class submarine
• Teardrop hull