 |
|
Common noise sources and paths Pilot House: Aft Deck: Sleeping spaces: |
Downeast Hulls
These popular hull types provide a platform for a variety of vessels, including workboats, charters vessels, sportfishers, and cruisers. No matter how you use your boat reducing noise will make your time onboard more enjoyable, productive, and safer.
Over the past 30 years, Soundown has developed extensive experience in reducing noise aboard boats of all hull types. We’ve used that experience to develop this list of recommendations for dealing with the most common noise sources. While no two boats are identical, this list will get you on course towards a quieter vessel. Path is also spelled out – whether the noise is travelling through the air or through the hull itself makes a big difference in how we go about remediating it.
Treatment: Engine room insulation
Path: Airborne
Source: Engine
Improved areas: Salon, cabins, aft deck
Problem: Engine noise is transmitted through the deck and bulkheads to cabins and on deck areas. Bulkheads and decks, even those with high density cores, do not provide sufficient noise blocking ability to provide comfortable noise levels. The broadband nature of airborne noise form the engine can be generally bothersome, but is particularly troublesome for speech intelligibility.
Solutions:
- Barrier composite insulation on the overhead and bulkheads. Barrier composites sandwich a layer of mass-loaded vinyl with acoustic foam. The foam absorbs noise while the mass-loaded layer reflects noise back into the engine room, protecting accommodation areas. Soundown’s IVF (insulated vinyl/foam) composite sheets are highly effective aboard most vessels and are easy to install in new builds or during refit.
- Best bet: 2” 2lb vinyl foam composite – good; 3” 2lb vinyl foam composite – bettter.
- For hull sides or fuel tanks outboard of the engines we recommend Soundown’s IAF acoustic foams. IAF does not feature a barrier – the foam absorbs noise in the machinery space resulting less noise in the accommodations. It’s also effective at reducing airborne noise that is transmitted to on deck areas the air vents.
- Best bet: 1”
- For a high level of finish and additional noise reduction, Soundown QuieTech perforated aluminum sheets can be installed over the insulation.
- QuietClad damped aluminum. We developed this system for larger vessels where a hard finished surface is standard. The QuietClad damped aluminum sheet provides both a clean white finish and excellent noise blocking properties, especially when used in conjunction with QuietStrips and acoustic fill.
Treatment: Exhaust
Path: Airborne
Improved areas: Aft deck, where most people spend the majority of their time on downeast boats, is generally affected by exhaust noise more than any other kind.
Problem: Even vessels equipped with basic mufflers experience significant levels of exhaust noise on deck, and the distinct tonal quality of exhaust noise is particularly bothersome to human ears. Downeast boats generally have above water exhaust, which is particularly loud when the engine is running.
Solutions: Soundown’s range of Axial Waterdrop silencers are tuned to the specific frequency of your engine. The right Waterdrop will typically drop exhaust noise to a level and frequency similar to the air and water noises created by the boat’s motion. With noise reduction as high as 25dBA, wind and water noise become the dominant sounds at cruising speed, and at slower speeds deck areas become much more comfortable.
- For vessels that spend a significant amount of time at sea, quilted fiberglass provides acoustic insulation that also meets relevant fire safety standards. The scrim and facing add cohesion to the fiberglass, which helps not only improves fire resistance but also makes the material easier to work with.
- Best bet: quilted fiberglass composite insulation
Treatment: Structure-borne Noise from the Engine
Path: Structureborne
Improved area: All areas
Problem: Vibrational energy from the engine is transmitted into the vessels structure and radiates into the vessel. While vibration from the engine cannot typically be felt the same way a bent shaft, or damaged prop can, it is a major component of the noise one experiences onboard. Because this energy travels through the structure and radiates off the top surface of the sole or accommodations side of the bulkhead it is not blocked by engine room insulation. (This is known as a flanking path.)
Solutions:
- Vibration Isolation Mounts for the engine.
Vibration Isolation Mounts (also known as soft mounts, or resilient mounts) decouple the engine from the hull, isolating a significant amount of vibration. Space constraints usually mean that engine and gear boxes are close coupled and require a mount that can handle the force of the propeller thrust. Our Rubber Design TT mounts use a series of rubber plates in shear, to provide isolation when positively or negatively loaded. Selecting the right one depends not only on the weight of the engine, but also the horsepower and torque.
Best Bet:
- TT3 Mounts for less than 1000 Horsepower engines
- TT1 Mounts for more than 1000 Horsepower engines
Treatment: Propeller Shaft
Path: Structureborne
Improved area: All areas
Problem: As the gear teeth make contact to turn the propeller shaft the vibration caused by each impact travels down the shaft and is transmitted into the hull. This can result in a high pitch gear whine that is noticeable throughout the boat. While this type of noise is not particularly loud its distinct tonal nature is particularly annoying.
Solutions:
- To break the transmission path and prevent vibration noise from traveling down the shaft, you can add an RD flexible shaft coupling. These coupling include rubber bushings which break the transmission path by isolating the shaft from the gear.
Best bet: RD flexible shaft coupling
Treatment: Interior soles
Path: Airborne & structureborne
Improved areas: Salon, cabins if any.
Problem: Structureborne noise is transmitted through the hull and radiates off the soles, producing noise. Treatments that go above the deck are particularly effective against these vibrations.
Solutions:
- Soundown premium carpet underlayment, an alternative to standard carpet padding, provides plush foam padding that decouples a denser mass layer from the deck. The sole, carpet underlayment and carpet work together to create layers of sound absorption and blocking. Carpet Underlayment comes in a variety of thicknesses to accommodate your headroom requirements. While thickness constraints mean carpet underlayment is not a replacement for good engine room insulation, it can be a good upgrade to boats with well insulated engine rooms or a quick, easy first step for boats where engine room insulation isn’t enough.
The ease of installation makes this treatment an easy upgrade for any vessel.
- Best bet: ½” 2lb Premium Carpet Underlayment
- Floating soles. For vessels seeking the highest level of noise reduction to produce extremely quiet interiors, floating the salon and /or lower deck soles is a must. In the detail below you can see how QuietStrips are used to isolate the QuietCore sole from the vessel’s structure. . This is especially effective with wood or vinyl flooring, where an added ¼ inch of damping material on top of the subfloor can absorb energy before it radiates off the deck. This installation would then have quarter-inch plywood flooring on top of the subfloor.
Engine room noise leaking through bulkheads
Path: Airborne & structureborne
Improved areas: Cabin forward of engine room
Problem: Depending on the proximity of the cabin to the engines, good engine room insulation may not be enough. This culprit is typically the high level of structureborne vibration in the bulkhead which radiates into the cabin.
Solution: By floating the interior panel, we can break the path of that vibrational energy, reducing interior noise.
- The detail below shows a floated bulkhead.
Treatment: Propeller Noise
Path: Structureborne
Improved areas: Aft cabin, aft deck
Problem: As each blade of the propeller passes closest to the hull it creates a pressure pulse which transmits energy to the hull. This effect becomes more pronounced as the propeller tip gets closer to the hull. If possible the clearance between the propeller and hull should be 15-20% of the diameter to avoid excessive prop noise.
Solutions: Damping tiles. These tiles are moderately malleable and can be shaped to follow the bilge. 3/8” can work, but 5/8” will be even more effective, if you have the clearance. Ideally, you want to take the length of the propeller, double it, and protect 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
Also, you want to make sure that the deadwood is faired near the propeller, so that the flow of water is even and consistent and you don’t get cavitation, which can cause serious noise in the propeller area.
Treatment: Head and hull liner
Path: Airborne
Improved areas: Interior spaces
Problem: Machinery noise that is transmitted into the accommodation areas of the boat will reverberate off hard surfaces such as bulkheads and overheads. This amplifies the noise in the cabin and can make communication difficult.
Solution: Soundown’s Head and Hull Liners produce an effect that’s like comparing an empty room to one with a carpet, curtains, and other soft finishes that absorb reverb. Headliners from Soundown are designed to be easy to install and provide an aesthetically pleasing finish.