[feadship]

any new ideas on noise reduction for aluminum yachts? trying to decide between the various foam sandwiches like those from Soundown and others and the solid rubber type blockers such as Accoustiblok? application is inside of hull including accomodations, engine room, lazzarette, etc.

[Codger]

There are a couple of different issues here.
One is physical/mechanical vibration.
The other is noise. They do overlap somewhat.:-)

Physical/mechanical can be reduced by passive damping and or isolating the source.
Noise cancellation can be achieved even in an industrial plant situation by broadcasting out of phase signal based on the original noise sources.

There is some new technology for active rather than passive damping on the near horizon that I've been hearing whispers about that may be applicable. I'll post a link when it's public.

[emilios]

Try contacting Halyard at www.halyard.eu.com , they are supposed to be very good at reducing all sorts of noise and vibration

[dogsharks]

Impact noise can be "deadened" by putting on the same kind of asphaltic and fiber composition board used in dampening automobiles. Sometimes this is now a plastic material, but the idea is to give the "tin drum" some body so it won't vibrate and "ding" quite so loud.

To reduce noise where the source of noise is in the room with you, thereby reducing the noise that might escape into adjoining rooms, etc., you can us a material that has a good NRC (noise reductiion coefficient). A material that has a NRC coefficient of .95 means 95% of all the sound that goes into the material will stay in that material. Often this is made of something like a 7-pound density fiberglass board, with a fabric cover over it. Certain types of commercial grade architectural ceiling tile will provide a NRC of .95, for instance, and this often looks like fiberglass duct liner board when you peel off the acoustically transparent fabric facing. Putting some of this in a noisy engine room would reduce the noise in the room to some extent.

Now on the other side of the room, if you want to reduce the ability of the noise to penetrate a wall, then you have to add mass. You can use lead sheet, or any other composition material that will add enough mass to keep a 60-cycle or other penetrating sound from zinging right through a wall like it wasn't there.

Parallel surfaces of similar material will vibrate together, and will be ineffective, for this reason you will find all recording studio glass control room windows use glass of different thicknesses, and these will be put at differing angles.

One last issue, is the potential need to decouple noise producing elements that may be transmitting sound "directly" to the structure of the boat, etc., and using it as a sounding board. If you have a high pitched pump, for instance, like a servo on an Airbus that you can hear so loudly in the cabin, you should not only put the pump on an acoustic isolator, you should also decouple the pipe itself from the hull structure too, as the sound will be transmitted directly to areas where it can be magnified and transmitted throughout the boat.

Hope this helps a bit.

Regards, dogsharks

[slappincapn]

There is a newer product that is non-degradable and made from woven and spun polyester. The company is in New Zealand and it is unique in its composition. I don't know much about it but some samples were returned to me from the IBEX show in Holland. I has a lead vinyl base and or sandwich. Unfortunately - I can't seem to locate any literature or even the name of the company.

Greg

[Yachtguy]

Originally Posted by feadship

any new ideas on noise reduction for aluminum yachts? trying to decide between the various foam sandwiches like those from Soundown and others and the solid rubber type blockers such as Accoustiblok? application is inside of hull including accomodations, engine room, lazzarette, etc.

Does anyone have any information on comparisons between Aluminum and Cored fiberglass hulls and superstructures when you consider acoustic and thermal insulation. I know the general opinion is that aluminum has a higher strength to weight ratio. But when you consider the insulation factor and that cored FRP uses the insulation as a structural core how does it compare. I am thinking hulls 80 feet and over say up to 140 feet.