- Acoustic signature
Acoustic signature is used to describe a combination of acoustic emissions of ships and submarines.
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.
Cavitationnoise: noise generated by the creation of gas bubbles by the turning of a ship's propellers.
Hydrodynamicnoise: 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.
Hydrophones and Sonaroperating in passive mode can detect acoustic signals radiated by otherwise invisible submarines, and use these signals to target attacks.
naval mines and torpedoes such as the CAPTOR minecan 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.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. 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.
*decoupling the machinery from the hull by mounting machinery on rubber mounting blocks.
propellers to reduce cavitation, 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.
For a time the
Royal Navytoyed with the idea of the trimaranhulled Future Surface Combatant. 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-electricpower plant; with the diesels being placed in the superstructure to mechanically isolate them from the water. This project got as far as the construction of the research ship RV Tritonto test the principle of a large scale trimaran design.
Type 45 destroyer
Upholder/Victoria class submarine
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