The hum of a two-stroke engine can make a pleasant day on the water a test for the nervous system. Even modern four-stroke models make sounds that cause fatigue when exposed to prolonged exposure. Many boat owners are thinking about how to make their stay on the water more comfortable without resorting to expensive service centers.
Self-manufacture noise-insulating cap It's a proven way to lower the decibels and protect the unit from dust, but simply applying the material is not enough: you need to understand the physics of sound propagation and the way the cooling system works. In this article, we'll discuss how to properly create effective protection without harming the motor.
The principles of sound insulation and the physics of sound
Sound emitted outboard motorIt's made up of mechanical vibrations in the cylinder block, exhaust noise and the intake system, and to deal with that effectively, you have to understand the difference between sound absorption and sound insulation, and absorption turns the energy of the sound wave into heat, and the insulation reflects the sound back.
It's critical for an outboard motor to use a combination approach, so if you just wrap the engine in a dense material, the heat will stay inside, which will cause it to overheat. cap-piece It should include a layer that quenches the vibrations and a layer that reflects the sound wave outwards.
It's important to consider that the main source of noise is often in the bottom of the lower unit, but it's the casing (hood) that resonates like a drum. The metal or plastic walls of the regular casing amplify the sound. Our job is to untie the rigid bonds and absorb the echoes inside the casing space.
⚠️ Attention: It is strictly forbidden to block air access to the carburetor or air filter. The engine must "breathe", otherwise a violation of the mixture will lead to loss of power and increased fuel consumption.
The heat mode is something that beginners forget: Two-stroke motors are cooled with off-water, but the crankcase and silencer release heat into the air under the casing. Temperature conditions It must remain within the operating limits even with insulation.
Selection of materials for marine conditions
An aggressive marine environment dictates its material requirements. Conventional building foam will quickly become unusable from moisture and salt mist. You will need specialized solutions that are resistant to water, oil and ultraviolet.
- 🌊 Vibrosplast or analogues on a bitumen-mastic basis with foil - for the primary pasting of metal surfaces of the casing.
- 🛡️ splendor or isolyte with a closed cellular structure - does not absorb water and perfectly retains heat.
- 🔇 Acoustic felt with moisture-repellent impregnation - to absorb high-frequency noise inside.
When choosing vibroisolator Pay attention to the temperature range. It can be hot under the hood of the motor, and cheap materials can leak, staining everything around and losing properties. A quality bitumen layer remains elastic and sticky for years.
Do not use open-porous materials such as conventional foam or mineral wool without protection. Once wet, they will become heavy, stop working and can cause corrosion of engine parts. Closed cell - key parameter.
⚠️ Warning: Some types of adhesives and solvents are aggressive to plastic casings. Before applying, check the reaction of the material in an inconspicuous area to avoid melting the structure.
Preparation of the casing and tools
Before you start, you have to remove the engine casing, and it's very inconvenient and inefficient to work on a weight or on a boat, and you're going to need a clean, well-lit room with a flat surface.
For high-quality task preparation of the following set:
- ✂️ Sharp scissors or a construction knife for cutting materials.
- 🧹 Degreasing agent (alcohol or special composition) for surface preparation.
- 🔥 Building hair dryer for better fit of vibration insulation (optional, but desirable).
- 📏 Line and marker for accurate marking of patterns.
Wash the inside of the casing thoroughly, mud, oil and dust reduce adhesion of the adhesive layer, and after washing, be sure to dry the surfaces. adhesion The main enemy of the peeling of materials in the future.
Remove all plastic elements, handles and latches if they interfere with access to the inner wall. Your goal is to access the maximum area of the inner surface of the lid.
Technology of application of vibration insulation
The first layer is always a vibroisolator, and the task is to change the resonance frequency of a metal or plastic panel to make it more deaf. Cut it into comfortable pieces, don't have to seal the surface with one large sheet.
Stick the material carefully with a roller or tool handle. There should be no bubbles of air. Pay special attention to the angles and ribs of stiffness, which is where rattles most often occur. Ride-up It provides up to 50% efficiency of the material.
If you use a bitumen-based material, you can warm it up a little bit with a hair dryer before you stick it in, which makes it more viscous and allows you to fill in the roughness of the surface, but don't overdo it with the temperature so you don't damage the plastic of the casing.
☑️ Checking the quality of the pasting
Cover about 60-80% of the surface, and a solid 100% surface area is often excessive and only makes the structure heavier, and the main thing is to treat the central parts of the panels, where the amplitude of the vibrations is maximum.
Sound-absorbing layering
And you put a sound absorber layer over the vibration insulation. plein Or special acoustic mats, and this layer should be solid, closing all the gaps between the pieces of vibration isolation.
When opening, consider the thickness of the material. Too thick a layer can interfere with the normal installation of the casing on the engine or block access to candles and other components for maintenance. The optimal thickness is 5-10 mm.
For areas around the exhaust pipe, use heat-resistant materials. Conventional polyethylene foam can melt from the heat of the silencer. heatproof Or special screens.
| Materials | Thickness, mm | Weight, kg/sqm | Temperature conditions |
|---|---|---|---|
| Silver Vibroplastic | 2.0 | 3.0 | -50...+70 °C |
| Spleen 3004 | 4.0 | 0.05 | -60...+80 °C |
| Bimast Standard | 2.0 | 4.2 | -40...+49 °C |
| Acoustic felt | 10.0 | 0.5 | -50...+150 °C |
Try not to close the process openings if they are designed for water runoff or ventilation. If there are such holes, paste them around the perimeter, leaving the center free, or use perforated materials.
Use a pattern of cardboard before unveiling the expensive material to get exactly into the complex geometric shapes of the inner niches of the casing.
Assembly and final inspection
After the glue has completely dried out (if additional glue has been used), install the casing on the motor, check if it sits freely in place, if it does not affect the control traction and the gas cable. Mechanical gaps should remain the same.
Start the engine on land (in a barrel or on a special stand) and let it work for a few minutes. Listen to the changes in sound. The hum should become deafer and lower, metal ringing and rattling of plastic will disappear.
Check the temperature of the casing after 10-15 minutes of operation at medium speeds. It should not be so hot that it is impossible to touch. Heat transfer - critical safety parameter.
If you notice the smell of burnt rubber or plastic, immediately turn off the engine and check if the insulation of the hot parts of the exhaust system is not affected.
Alternative methods of noise reduction
The oaking of the casing is not the only way, but there are other methods that can be combined to achieve better results, such as installing a better muffler or adjusting the carburetor.
Excessively rich mixture can increase exhaust noise. Adjustment carburetor The manual often lowers the volume of the engine, and it's also worth checking the state of the spark plugs.
- 🔧 Replacement of the standard muffler with an upgraded version with a large volume.
- ⚙️ Adjustment of valve gaps (for four-stroke motors).
- 🌲 Installation of the engine on softer damper pads of the transom.
⚠️ Warning: Making changes to the exhaust system may violate environmental regulations and result in loss of manufacturer warranty.
The combination of the right engine setup, the right insulation of the casing and the vibrating of the transom will allow you to enjoy the silence on the water.
Effect of the screw on noise
An improperly selected screw can cause cavitation, which creates additional noise. Check the pitch and diameter of the screw for your load mode.
High-quality noise insulation reduces operator fatigue and allows better hearing of the environment, which increases safety on the water.
Frequently Asked Questions (FAQ)
How much louder will the engine become after the scaling?
The noise reduction is typically between 3 and 6 dB, which is subjectively perceived as almost halving the volume, but the result depends on the initial state of the engine and the quality of the work performed.
Can the engine overheat due to insulation?
With the recommended materials and the technology (not to block the air intakes), overheating is unlikely, two-stroke motors are cooled with water, and heat transfer to the air is secondary.
How long will this noise insulation last?
Quality materials (vibroplastics, splints) last 5-7 years or more, but in an aggressive marine environment, the period can be reduced to 2-3 years, after which partial replacement of the coating may be necessary.
Is it difficult to remove the casing for maintenance after completion?
If you don't put glue on the spark plugs and make the insulation layer too thick, it's not going to be difficult. The skin has to be removed as easily as it was before the modification.