Pilot / Patrol Boats

Pilot / Patrol Boats

Pilot boats need to be able to operate comfortably in a wide range of conditions, and communications are vital for safety. On small, tough single-engine boats, reliability and communications can be crucial for the safety of crew and passengers. Whether you’re a pilot trying to board a ship or a military or fire rescue boat on a mission, hearing clearly can be a life-saving priority.

For small military craft, these measure will also help meet pass-by noise requirements for aural detectability, and some of these treatments – especially risers and silencers – significantly reduce a vessel’s thermal signature.

Treatment: Machinery Space Vibrations

Path: Structureborne

Source: Engine / Machinery Space

Improved areas: Entire vessel.

Problem: The horsepower to vessel size ratio on a pilot or patrol boat is very high, and the resulting vibrations typically transfer throughout the boat, becoming dangerous noise. The engine itself also produces airborne noise at high volume, and can produce a whining noise from the propeller shaft because of the torque tension placed on the metal.

Solutions:

• Mounting the engine is the single first solution you should examine. Depending on the engine size and thrust, any solution from TT mounts to conicals might be best. Because there is typically little room for interior insulation, or finish, the mounts have to bear the brunt of the noise reduction.
• The right mounts work best in tandem with an oil bath or separated shaft system. We recommend our Evolution Shaft System, which works with TT mounts in a standard configuration, but is best with coinical mounts.
  Specifications

Best bet: An Evolution Shaft System and 315 conical mounts

Treatment: Machinery Space Noise

Path: Airborne

Source: Engine / Machinery Space

Improved areas: Entire vessel.

Problem: The engine also produces airborne noise at high volume, which is carried by airflow throughout the vessel.

Solutions:

• The machinery space is typically tight, and air moves quickly through it. Duct noise can be affected by strategically placed filters and insulation in particular problem areas. Adding turns or loops to a ventilation system will also reduce sound. To reduce noise transmission, you want to make sure there is no direct line of sight between a ventilation source and a vent. If there is, we suggest making a baffle to break the line of sight with one or more 90 degree turns.
  
  Note: some air intakes are necessary to let the engine breath and prevent overheating. These should not be sealed up.

• Best bet: 1” foam on vents, where it will fit, and at strategic points to help break line of sight and wind tunnel oriented areas.
  Specifications

Treatment: Exhaust System Vibrational Noise

Path: Structureborne

Source: Engine exhaust path

Improved areas: Entire vessel, particularly any parts close to the exhaust system.

Problem: As exhaust moves through the system, it creates vibrational energy which passes through every piece of the structure it’s attached to. This ultimately manifests as undesirable sound in any adjacent spaces. This can affect communication with people on deck – while maneuvering, for example, which becomes a vital safety item.

Solution:

• Water Drop Silencers will make a substantial difference. Usually, axial waterdrops are a best bet given normal space constraints, but every engine configuration is unique – call for a consultation before ordering a silencer.
  Specifications
  
  Note that silencers also reduce the thermal signature of a military vessel.

Treatment: Propeller Noise

Path: Airborne

Source: Propellers

Improved areas: Deck areas nearest the propellers.

Problem: Smaller aluminum hulls are particularly susceptible to reverberation from fast-rotating propellers. As a rule, if the clearance between the propeller and the hull is smaller than 15% of the propeller’s diameter, you will experience a significant noise issue. 20% clearance is preferable.

Solution:

Damping tiles placed over the propellers deflect and reduce soundwaves of this frequency. These tiles are malleable and can shaped to follow the bilge. 3/8” can work, but 5/8” will be even more effective. Ideally, you want to take the diameter of the propeller, double it, and treat a square patch that size right above the propeller (so, if you have a 24-inch propeller, cover a 48-inch by 48-inch square with damping tiles).

• Best Bet: 5/8” Damping tiles
  Specifications