COMMANDO BOAT NOISE

摘要

The paper discusses the issue of engine noise level in maritime and riverine operations carried out by military and governmental vessels. As a part of an ongoing big project authors investigate noise levels produced by different vessels like Combat Rubber Riding Craft with outboard engine (FC 530 Zodiac Commando Boat), Rigid Hull Inflatable Boats (military type), both with outboard engines equipped with screw propellers and inboard engines with water jet propulsions. Tests are carried out in different meteorological conditions, sea states as well as at different distances and directions from the noise source. During tests the vessels were cruising with various speeds. In this paper only FC ZODIAC 530 riding craft acoustic results are presented. This vessel remains the basic means of transportation during covert operations, both at sea and on inland waterways, for mid and short distances. Other Polish military fast RHIBs subjected to the tests were designated and built especially for Polish Special Operations Forces by different manufacturers. Therefore most of the results for RHIBs obtained by the authors are restricted and data access requires special security clearance to be granted to all personnel involved into this acoustic survey. FC ZODIAC 530 is a vessel which is commonly known throughout the world and can be purchased by many military units and governmental agencies, thus its sound characteristics may be considered as unclassified. Noise generated by boat engines is a crucial factor when conducting covert Water-borne Operations. When a mission requires a silent covert approach to the target placed at sea or at the shoreline, the engine noise must be considered and kept below a certain level. In the planning phase of every such operation, military or governmental personnel is bound to determine zones at which boat crew should decrease the speed or completely shut down the engines and continue with their paddles in order to go undetected. The actual range of the zones depends on factors such as: engine type, vessel's velocity, weather conditions (wind, mist, rain, cloudiness etc.), time of the day, as well as moon phase and sea state with the background noise created by waves, wind and artificial environment. Noise level produced by boat engines is one of the factors that require specific "at sea" and "on river" testing and detailed evaluations. Modeling boat engine noise helps to plan in advance the optimal way of boat usage during convert missions.