How to insulate ships propeller noise

Insulating propeller noise and isolating vibrations
Propeller noise is caused by vibrations of the driveshaft, movement of water, cavitation, and resonances of the bow thrusters. These vibrations become audible via the ship’s stern, hull, transom and in case of bow thrusters, the skin of the ship in the front. Especially the smaller thrusters in yachts are very audible. 

How to insulate propellor noise
The insulation of propellor noise is actually done by isolating vibrations. To reduce propeller noise you need to apply an acoustic method called anti-drumming. There are two products you can choose from. Let’s start with the best one, but also most difficult to use and apply.

Isolation of vibrations in a steel ship’s hull
This method and products, Vibradamp and Zincor, are suitable to isolate vibrations in the stern, the bow thrusters and tunnel of a steel ship. Start by removing rust, loose coating or paint and clean the surface that you want to insulate. All parts should be as clean as possible! Vibradamp Compound consists of two components, these need to be mixed in a ratio of 1:1, One bucket of Vibradamp, component A, mixed with one bottle of component B. Mixe the two until the product has a uniform beige/bronze colour. Once mixed you have an hour until the hardener sets in!  

Apply this mixture at least one meter surrounding the propeller and/or bow thrusters, more is better. In luxurious yachts almost all of the ships stern in the engine room is treated this way for maximum performance. When you apply Vibradamp it should be in a ratio of 1:4:4, this means that for every 4 mm steel (thickness) you apply 1 mm Vibradamp compound and 1 mm Zincor steel plates. Next step is pressing the Zincor steel plates into the Vibradamp compound. This can be done within a few minutes after applying the compound. Keep some distance between each plate of about 10 to 15 mm.

The result of this method can take a few days before it becomes noticeable. It takes some time for the product to fully harden underneath the steel plates. When fully hardened you can paint the compound and Zincor plates.

Isolation of vibrations in a polyester boat or yacht
In principle you need to insulate the same parts as in any other ship, the transom, hull and surroundings of the propeller and thruster, and at least a meter around it. Make sure the polyester is flat and a bit roughened and thoroughly cleaned. Instead of using Vibradamp you can also use the mass loaded vinyl Isomat TS14. This product will also add a lot of mass and insulation. Isomat TS is used in combination with Saba Glue, apply a layer of this contact adhesive and let it dry for a few minutes. Then, press the Isomat firmly onto the surface and tap it with your fist or a rubber mallet to avoid air bubbles between the Isomat and the surface and for a good adhesion.

Products to insulate and isolate propeller and thruster noise