What is the problem? Isolating the propeller noise is done in the same way as insulating the ship's hull: by means of sandwich suppression or by adding mass to the ship's hull polyester or hull. Resonance arising from, for example, the propulsion system such as the propeller and bow thruster are transferred to the hull and cause noise problems all over the ship. The best solution is to insulate the ship's hull. This method of insulation is called sandwich anti-drumming. The term anti-drumming indicates that the surface doesn't move so that vibration cannot travel through the sheet material.
What is the solution for the steel ship hull? Free the ship's hull from rust, grease and dirt (paint/coating can remain). Then, apply Vibradamp A-90-P two component paste using a ratio of 1:1:4. This ratio implies that for every 4 mm steel (thickness) you apply 1 mm paste and 1 mm Zincor steel plates. The Zincor steel plates function as counter plates and are pressed into the paste with a mutual distance of 10 mm. Now, the steel doesn't move anymore, greatly reducing the gong sound. It takes a few days before the Vibradamp under the steel plates has fully cured, after which the full effect will become noticeable.
What is the solution for the polyester ship hull? Make sure the polyester is flat and roughened and then thoroughly cleaned. Polyester is lightweight material, allowing vibration to be easily transferred. Consequently, adding mass will greatly reduce this. In addition to the application of Vibradamp sandwich anti-drumming, you can also choose to use the plastic mass plate Isomat TS14. Equip the surface and the Isomat with a layer of Contact glue 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.