Noiseproofing outboard motor: 7 proven ways to make the boat quieter

Why engine noise insulation is not a luxury, but a necessity

Have you ever been frozen on a fishing trip because you roared? two-stroke Or you'd come back from the pond with a headache because the vibrations were so bad. Yamaha 15 LMHS The noise insulation of the outboard motor is not about comfort (although it is about it too), but about comfort. Real increase in catch by 30-40% by reducing acoustic pressure on water. Bauman MSTU They show that outboard motors with a capacity of 9.9 hp create noise up to 95 dB – this is the level of a running chainsaw!

But it's not just the fish that's the problem, and the constant vibration is destroying the motor's mounts, speeding up wear on the bearings, and can even cause cracks in the hull of the boat. aluminum or polyethyleneAnd if you use a boat for family trips, 2-3 hours of engine roar is a sure way to ruin your vacation, and fortunately, modern materials and technology can reduce noise by 60-80% without loss of power and at minimal cost.

Top 5 sources of noise in the outboard motor (and how to eliminate them)

Before you rush to buy soundproofingYou need to understand what's rattling in your motor, and here are the main culprits of noise, ranked by exposure level:

• 🔥 Exhaust system In two-stroke engines, the exhaust goes directly into the water through a propeller, creating a bubble effect and a resonating hum.
• 🛠️ Vibration of the hull It's transmitted through transom mounts, especially critical for aluminum boats with thin walls.
• ⚙️ Reductor and bearings - worn parts create a metal grinding at high speeds.
• 🌊 Screw cavitation The resulting air bubbles burst with cotton, if the screw is selected incorrectly.
• 🔧 Resonance fluctuations When the vibration frequency of the motor coincides with the boat’s own frequency (the “singing deck effect”).

Interesting fact: in motors Mercury and Tohatsu After 2018, the vibration problem was partially solved by the rubber-metal sleeves in the mounts. Salut-M or Wind 8 Noise insulation is not provided at all - you will have to do everything yourself.

Materials for noise insulation: what works and what – money for the wind

The market offers dozens of noise insulation materials, but 80 percent of them are either useless for outboard motors or will make things worse. foam or polyethylene They only absorb sound at high frequencies, and they'll let the low-frequency hum of the exhaust pass without changing.

Materials	Efficiency, dB	Cost, /m2	Where to apply	Cons
vilatherm (Plastic foam)	12-15	250-400	Blob pasting, internal surfaces	Fear of gasoline, requires waterproofing
SPL-300 noise (bitumen + rubber)	18-22	600-900	Trans plate, motor mounts	Heavy, difficult to glue at low temperatures
Acoustic felt (basalt fiber)	25-30	1200-1800	Inside bonnet, exhaust pipe	It absorbs moisture, it needs vapor insulation.
Silver Vibroplastic (aluminum + bitumen)	10-14	500-700	Motor body, gearbox	Effective only in combination with other materials
Liquid noise insulation (for example, Noxudol 3100)	8-12	1500-2500	Complex surfaces, welded seams	It's drying for a long time, it needs painting.

Use it for maximum effect combination: vibrating layer (e.g., SPL-300 noise) + sound-insulating (Acoustic felt) + seam sealing (NoxudolThis pie will reduce noise by 25-30 dB, which is the level of quiet conversation instead of the roar of a chainsaw.

⚠️ Attention: Never use the engine for noise insulation. mineral-wool or foamThese materials are fueled, and when heated, they emit toxic substances, and the foam crumbles with vibration and can clog the cooling system.

Step by step: noise insulation of the outboard motor yourself

If you decide to make noise insulation yourself, here is an algorithm for actions to be taken. outboard (by example) Honda BF20 or Tohatsu MFS25The whole process will take 6-8 hours and cost 3-5 thousand rubles.

Remove the motor from the transom and clean the dirt | Demount the hood (carefully so as not to damage the latches) | Degrease the surfaces with acetone or white spirit | Purchase materials (see table above) | Prepare tools: scissors, roller, hair dryer, brush--->

Step 1. Vibroproofing of anchorages

On the transom plate of the boat and the place of fastening of the engine stick SPL-300 noise or Vibrosplop GoldCut the workpieces by the shape of the parts, warm them up with a hair dryer (up to 50-60 ° C) and press them tightly, and pay special attention to the places where the metal comes into contact with the metal, where the vibration is transmitted most strongly.

Step 2. Noiseproofing the hood

Plug the inside of the hood vilatherm (thickness 10 mm) or Acoustic feltFor the best effect, make a two-layer design: the first layer is a vibration absorber, the second is a sound insulator. Don't forget the ventilation holes -- you have to leave them open!

Step 3: Exhaust system treatment

If you have a two-stroke engine, you can install it. silencer The exhaust pipe is suitable for four-stroke motors. acoustic felt And then you're going to have aluminum foils, so you don't get wet. Mercury and Suzuki After 2020, there are already regular silencers - they need to be additionally wrapped in isolation.

Step 4: Seam sealing

All joints and welds on the motor body miss fluid-proofing (for example, Noxudol 3100This will prevent the metal from resonating. After drying (24 hours), paint the treated areas with heat-resistant paint.

Noise insulation of a stationary motor: features and life hacks

With stationary motors (e.g., Volvo Penta or Yanmar) The situation is more complicated: they are installed inside the hull of the boat, and the noise is spreading through the water, the hull and the air at the same time. isolation:

• 🛡️ Engine vibration Replacement of standard fasteners with rubber metal shock absorbers (for example, VibraTechnics VT-30).
• 🔇 Soundproofing box - engine compartment plating sandwich-panel (aluminum + soundproofing + aluminum).
• 🌊 Exhaust waterproofing installation water-jet (for example, Jabsco) to quench bubble noise.
• 🔧 Pipeline damping - winding of fuel and exhaust pipes specialty It's made of silicone rubber.

For boats with cabin (for example, Kazankah-5M or Ob-4M) additionally, the bulkheads between the engine compartment and the cabin will need to be isolated. Rockwool sound-absorbing panels (thickness 50 mm) with a skin of plywood.

⚠️ Attention: When installing a soundproofing box around a stationary motor, be sure to provide ventilationMotors! Yanmar 3YM30 and similar with a lack of air overheat in 15-20 minutes, which leads to jamming of pistons.

Tuning exhaust system: how to make the engine quieter by 50%

Exhaust is the main source of noise in outboard motors. In two-stroke engines, it has no silencer at all in the classical sense: exhaust gases go directly into the water through a propeller. But even here there are solutions!

Method 1. Installation of a muffler-resonator

For motors with a capacity of up to 30 hp, a homemade stainless tube muffler (diameter 50-60 mm) with perforation and stuffing from basalticThe pipe is attached to the exhaust pipe through a flexible adapter. Sierra model 18-7836or Attwood.

Method 2. Water-gunned muffler

Effective for motors from 40 hp The principle of operation: exhaust gases pass through the water in a special chamber, which extinguishes the sound by 20-25 dB. Jabsco 35010 or Groco VW-1Minus: The exhaust resistance increases, which can reduce power by 2-3%.

Method 3: Reconfigure the exhaust

In engines. Evinrude E-TEC and Honda BF You can reconfigure the timing phases so that the exhaust occurs when the propeller creates maximum resistance to water, which reduces noise by 8-12 dB, but requires intervention in the ECU (electronic control unit).

How to check the effectiveness of the silencer?

To assess how quiet the motor has become after installing the muffler, use a free noise-meter app (for example, a small number of people). Decibel X Measure the noise level at idle and at 3000 rpm at a distance of 1 meter from the transom. The difference before and after should be at least 10 dB. If less, the muffler is installed incorrectly or does not fit the parameters.

Frequent noise insulation errors (and how to avoid them)

Even experienced boaters sometimes make mistakes that negate all efforts.

• 🚫 Use of one material - for example, only wilatherma The result is that the noise becomes mute, but the vibration remains.
• 🚫 Coverage of vents - leads to overheating of the engine and loss of power.
• 🚫 Incorrect installation of the silencer If the muffler is too long or narrow, the back pressure is created and the motor is pressed.
• 🚫 Ignoring anchorages If you do not isolate the transom plate, vibration will go through the hull of the boat.
• 🚫 Savings on materials Cheap foam or foam in a month turn into dust from vibration.

Another common mistake. lack of weightLike, if you put a hood on a motor. Honda BF5 (weight 27 kg) Acoustic felt (3 kg/m2), the total weight will increase by 10-15%, which will affect the handling of the boat.

FAQ: Answers to the most frequent questions

Can the engine be noiseproofed indiscriminately?

Yes, but the effectiveness will be lower.

1. Plug it in. bonnet vilatherm (thickness 5 mm).
2. Install. rubber-stick between the motor and the transom.
3. Pull on the exhaust pipe heat-resistant glass fabric.

This will reduce noise by 5-8 dB, but the vibration will not be eliminated.

Will the noise insulation reduce the engine power?

If it's done right, no.

• Installation water-jet It can reduce power by 1-3% due to resistance.
• Too thick insulation of the hood worsens cooling, which leads to knock-off and power loss.
• Additional weight (more than 5 kg) can reduce the top speed by 1-2 km / h.

In turbocharged engines (e.g., Mercury Verado) improper insulation can disrupt the intercooler - it is better to consult specialists.

Which motors are the quietest by default?

Based on the journal's tests Boats and Yachts. (2023), the quietest production engines:

1. Honda BF2.3/BF5 (Noise level 68 dB) - thanks to the system ECOmo And optimized exhaust.
2. Mercury 20/30 ELPT (72 dB) – four-stroke with silencer Quiet Cruise.
3. Suzuki DF20/25 (70 dB) – Technology used Lean Burn for smooth operation.
4. Tohatsu MFS9.8 (74 dB) - low-speed mode Eco-Operation.

Two-stroke motors (e.g., Parsun T2.6) not included in this rating, their noise starts at 85 dB.

Can I use car noise insulation for a boat?

Partly yes, but with reservations:

• ✅ Vibrosplast or bimast It is suitable for vibration insulation of fasteners.
• ✅ splendor (aluminum) can be used for the hood, but only with waterproofing.
• ❌ Accentuate or Shumoff. They are not afraid of water and water.
• ❌ Automotive noiseproofing (for example, Body 950) cannot withstand the constant vibration of the boat.

It is better to choose materials intended for marine (marking) Marine Grade).

How does noise insulation affect the engine life?

Quality noise insulation extends the life of the motor 15-20% by:

• Declining vibrational Bearings and gums.
• Decreases heat loss (The insulation works like a thermoscreen).
• Protection from corrosion (Sealing the seams prevents moisture from entering).

However, if the insulation is installed incorrectly (for example, the ventilation is blocked), the engine life is not sufficient. shrink This is especially critical for air-cooled engines (e.g., Salut-M or Whirlwind-30).