Exhaust Mountings

        

INTRO:
  In any case where diesel engines are used for propulsion or power, noise and vibration that is generated by the engine will travel along the exhaust trunking. If the trunking is solidly mounted this noise and vibration will pass directly into the ship's structure and will be radiated from accommodation walls as sound. A significant reduction in the radiated noise and vibration can be achieved by the introduction of rubber-metal elements between the trunking and ship's structure.

  Sound propagates through steel at approximately 5.000 m/sec. whereas through rubber the velocity is reduced to approximately 45 to 90 m/sec.

  By careful design of the mounting arrangement it is possible to obtain reductions of 8 to 10 dBA throughout almost the whole major frequency range of 63 to 4.000 Hz.

TYPES OF MOUNTINGS:
   - Flexible fixed points: take the static and dynamic forces whilst resisting or allowing expansions depending on their role in a particular system.

    - Stabilizers: allow expansion whilst stabilizing the piping within the ship's structure. In the case of horizontal piping the stabilizers carry the pipe weight.

  In order to protect the rubber from the high exhaust gas temperature it is necessary to incorporate adequate thermal insulation. It is essential to reduce the temperatures at the rubber-metal elements to less than 80 °C and in fact by using suitable insulation materials it is frequently possible to limit temperatures to a maximum of 50 °C.

  It is always advisable to provide an air gap (approximately 25 mm.) between the exhaust bracket and trunking. The above is appropriate for the flexible fixed points. For the stabilizers the thermal insulation is attained with the length of the threaded rod.