Constant hum outboard It can turn a pleasant fishing experience into a nervous system challenge, and many boat owners find that even expensive models of technology produce annoying low-frequency roars that are amplified inside the cockpit by resonance. noiseproofing A protective casing that not only reduces decibel levels, but also improves overall comfort on board.
The upgrade procedure requires careful selection of materials, as the operating conditions in the outboard unit are extreme. It is important to consider not only the acoustic properties of the insulator, but also its resistance to high temperatures, water and fuel. Properly done work can reduce noise levels by 5-10 dB, which significantly affects the fatigue of the crew during long transitions.
In this article we will discuss in detail the technology of preparation, the choice of optimal vibration and noise insulation You'll learn how to avoid the typical errors that can lead to overheating of the power unit or corrosion of metal parts. A competent approach to tuning the casing is the balance between silence and reliable operation of the engine.
Principles of work and choice of materials
The main source of noise in the outboard motor is vibration of the operating engine and exhaust gases transmitted to the thin walls of the plastic or metal hood. vibrodamping Vibrodamping materials, often called "vibra," convert the mechanical energy of the vibrations into heat, reducing the amplitude of the rattling walls.
The second layer is usually applied to a noise absorber, which works on the principle of absorption of sound waves. Foamed polyethylene Or a melamine sponge is great at handling high-frequency whistles and rustle, but it's critical for boats that all the components they use don't absorb moisture or break down from contact with gasoline or oil, and the usual foam is not going to work here, because it will quickly become useless.
⚠️ Attention: The use of flammable materials (e.g. conventional foam or untreated foam) near the exhaust system and carburetor can cause fire.
When choosing mastic For vibration insulation, you should look at bitumen-polymer compositions with aluminum foil. They provide the best mechanical loss ratio. For the upper layer, closed-cell materials, such as: isolyte They're inert to chemicals, they don't store water.
Surface preparation and dismantling
The quality of the materials adhesion depends on how carefully the surface of the casing is prepared. Before starting work, remove the lid from the lower unit and completely dismantle all attachments. This includes removing vomiting, pens, emblems and, if necessary, internal panels. Work should be carried out in a well-ventilated room at a temperature of not lower than + 15 ° C.
The first step is to thoroughly clean the inner surface of the plastic or metal, remove all dirt, traces of oil, lubricants and old insulation, if any. White Spirit or specialized antisiliconeThe use of aggressive solvents such as acetone on some plastics can cause the structure to become cloudy or break down, so pre-check the material's reaction in an unobtrusive area.
After degreasing, the surface should be completely dry. If there are scratches or chips on the plastic, it is advisable to clean them with fine sandpaper to improve the adhesion. Pay special attention to the stiffness ribs and the inner corners where resonance occurs most often. vibrodamping.
☑️ Preparation for noise insulation
Technology of application of vibration insulation
Applying a vibratory layer is the most time-consuming step, requiring patience and accuracy. The material is cut into strips or pieces of convenient size. Do not aim to seal 100% of the area with one solid sheet, especially on plastic casings, as this can disrupt the geometry of the cover when heated. The optimal coverage area is 60-80% of the surface, with an emphasis on flat areas and bracket attachments.
A hard roller is used to roll the material. Every piece of glued material must be smoothed carefully, ejecting air bubbles from under it. Badly rolled material will not work efficiently and may detach over time. Pay special attention to the edges - they must be pressed as tightly as possible. On complex embossed surfaces, the material can be preheated with a building hair dryer to a temperature of 40-50 ° C, which will increase its elasticity.
| Processing area | Type of material | Thickness of layer | Features |
|---|---|---|---|
| Upper plane | Vibroplast/Bimast | 2-3 mm | Maximum coverage |
| side-slips | Vibrosplast | 2 mm | Strips 50-70% |
| Ribbons | Vibrosplast | 2 mm | Point processing |
| Internal corners | Vibrosplast | 2-3 mm | Resonance removal |
It's important not to block the vents and the air intake channels. The engine has to breathe. It is critical to leave free zones around lower unit and in the exhaust gases where the temperature may exceed the permissible values for glue. If you use the material on a bitumen basis, make sure it doesn’t leak on a hot day, staining your clothes or boat deck.
What to do if the material does not stick?
If the vibration insulation is not good for the plastic, try to warm the material with a hair dryer and the surface of the casing slightly, and you can also use a primer for hard-to-glue surfaces, but only if it is not aggressive to the type of plastic in your motor, sometimes it helps to apply the material in small squares with careful edge rolling.
Laying of the noise-absorbing layer
When the vibra is done, it's the noise absorber's turn, and it's the layer that's placed on top of the vibration insulation or on the free plastic, and the materials that are best suited for outboard motors are the foil layer facing inwards to the motor, and the foil will reflect some of the heat and protect the noise absorber from oil and gasoline.
The material is cut along the contour of the inner surface of the lid. Unlike vibration insulation, you can and should aim to cover 100% of the area, because this layer does not require a tight roll and works to absorb the sound wave in its thickness. The joints of the sheets should be made minimal, and it is best to stack the material in one single piece, if the width of the roll allows.
When mounting around the ventilation ducts, you need to carefully cut the holes, the edges of the cutout can be glued with aluminum tape to prevent the material from sprinkling over time, make sure that the thickness of the added layer does not interfere with the tight closure of the cover and does not affect the internal mechanisms of the motor when the casing is installed in place.
For better tightness and protection from oil spray, a thin plastic film can be pulled over the noise absorber, fixing it at the edges with heat-resistant tape, but this is permissible only if there is a sufficient gap to the hot parts.
Features for 2 and four-stroke engines
The noise insulation process of two-stroke and four-stroke engines has its own nuances due to design differences. Two-stroke engines are usually noisier and vibrating. In these, exhaust gases are often removed through lower unit, but much of the noise comes from the crank mechanism. For these units, the thickness of the vibration insulation layer can be increased, because the vibration level is higher here.
Four-stroke motors work softer, but have a more complex gas distribution system and often a hotter casing due to the presence of a separate cooling circuit and oil in the crankcase. Heat insulation This is a very important part of the process, and it's also a very important part of the acoustics, and it's very important to keep a close eye on the temperature of the inner surfaces of the lid, and the use of aluminum materials here is particularly justified for reflecting heat.
In four-strokes, it's important to keep the air filter and the oil probe in check. They often have more complex casing designs, with lots of plastic ducts. When you insulate these engines, try not to disrupt the normal cooling pattern, which can be tied to the flow of air through certain cracks in the casing.
⚠️ Note: On four-stroke engines, it is forbidden to seal the areas around the muffler and exhaust manifold even with heat-resistant materials, unless they are certified for temperatures above 200 C. The risk of fuel vapor fire in this case is maximum.
Temperature control
The biggest danger in self-insulation is the engine's thermal balance. Outboard Motors are cooled by off-board water, but much of the heat is diverted through the cylinder surface and the exhaust system into the air under the casing. Thickening the hood walls by insulation can lead to overheating, especially at low strokes or when trolling.
After all the layers are installed, a test run is required, the motor must run at idle speeds for 10-15 minutes, at which time the temperature of the outer surface of the casing should be checked periodically (with caution), and if the plastic becomes scorching hot where it was previously warm, then the heat transfer is disrupted.
To prevent problems, it is recommended to leave technological gaps or even cut additional, grid-protected holes in the bottom of the casing to improve air circulation. Heat resistance If you smell the scorched insulation on your first start, you must immediately stop operation and conduct an audit.
The main purpose of noise insulation is comfort, not the creation of a "thermos" around the engine, and maintaining effective cooling is more important than an additional 2 dB of silence.
FAQ: Frequently asked questions
How much noise does this actually reduce after the procedure?
On average, you can reduce your perceived noise by 5-8 dB, which subjectively feels like a volume reduction of about two times, the main effect is achieved by eliminating plastic rattles and reducing the high-frequency components of sound, and the low-frequency hum of the motor will not be completely removed, since it is transmitted through lower unit to the transom of the boat.
Can I use car noise insulation?
Yes, but with caution, automotive materials (such as Vibroplast, Splen, Accent) are great for their properties, but make sure they are moisture-resistant and not afraid of contact with fuels. Conventional building materials may not withstand the specific conditions of use on water.
Will I lose my engine guarantee?
Formally, any interference with the design, including the sticker of materials on the inside of the casing, can be a formal reason for denial of warranty service if the dealer decides that this has affected the overheating.