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Boat Engine Compartment Insulation

Boat Engine Compartment Insulation Guide

Boat Engine Compartment Insulation Guide

If you’re fed up with the excessive noise on your boat, consider insulating the engine bay compartment. A boat’s engine is the number one cause of noise, and as you know, there is no shortage of noise while boating (#2: wind noise and #3: vibrational noise from water hitting the hull). All of these noises add up to make it harder to have a conversation with your friends and family, or even just to relax. Take a bite out of the biggest culprit of boat noise by soundproofing that loud engine and you’ll be much happier every time you take your boat out.

Even if your primary reason for insulating your boat’s engine compartment is to create a more pleasant boating experience, you should know that loud noise can turn into a health and safety issue also. Prolonged exposure to the level of noise that comes from boat engines can have serious consequences. We’ll get into it, but that’s why it pays to add additional insulation to your boat’s engine compartment — it’s safer and more enjoyable for all.

If you’re fed up with the excessive noise on your boat, consider insulating the engine compartment. A boat’s engine is the number one cause of noise, and as you know, there is no shortage of noise while boating (#2: wind noise and #3: vibrational noise from water hitting the hull). All of these noises add up to make it harder to have a conversation with your friends and family, or even just to relax. Take a bite out of the biggest culprit of boat noise by soundproofing that loud engine and you’ll be much happier every time you take your boat out.

Even if your primary reason for insulating your boat’s engine compartment is to create a more pleasant boating experience, you should know that loud noise can turn into a health and safety issue also. Prolonged exposure to the level of noise that comes from boat engines can have serious consequences. We’ll get into it, but that’s why it pays to insulate your boat’s engine compartment — it’s safer and more enjoyable for all.

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Popular Boat Soundproofing Materials


Boat Engine Compartment Soundproofing Kits
Damplifier Pro™ Sound Deadening Mats
Mega Block™ Sound Absorbing Foam + Heat Shield

The Benefit of Marine Engine Compartment Insulation

When you insulate your boat’s engine and create a more pleasant ride, you make it easier to do something that most Americans agree is relaxing: spending quality time by the water. In fact, a 2017 study by Wakefield Research (according to BoatUS Magazine) found that 4 in 5 Americans say being around the water relaxes them. Scientists then found that even just looking at water “can trigger feelings of wellness, compassion, empathy, and happiness.” BoatUS Magazine seems like they may be pretty pro-boat, but we’ll take them at their word on this one.

How does that relaxation get interrupted? With an overly-noisy boat engine. A boat engine is typically only about 60-65 decibels when idling, but quickly ramps up to around 80 decibels of noise at cruising speeds and over 100 at full-throttle for some boats. Studies show that continuous exposure to more than 80 decibels of noise can cause:

  • Nausea
  • Fatigue
  • Increased blood pressure
  • Insomnia
yacht on open water

This is me in my boat. Someday...

In fact, the Occupational Safety and Health Administration (OSHA) has set 90 decibels as the highest level a worker can be exposed to in your typical 8 hour work day. Every time the noise level is increased by 5 decibels, that hour limit is cut in half. So at 95 decibels, it’s 4 hours and then at 100 decibels, it’s down to 2 hours.

To put those noise levels in perspective, normal conversations can be heard with 70 decibels of background noise. At 85 decibels, you have to shout. And then at 100 decibels of background noise, you have to stand right next to each other AND shout to even have a chance.

Four Benefits of a Quieter Boat Engine

  1. More relaxing and more enjoyable rides
  2. Healthier rides due to reduced noise pollution
  3. Safer rides due to less distraction/inability to hear other boats.
  4. More legal rides if you need to comply with your state’s boating noise laws

When you’re out boating with the family and friends on your local lake or on the open water, why would you willingly subject yourself to those noisy conditions if you don’t have to? Let’s just nip in the bud right now so we can all relax and enjoy ourselves.

boat engine below deck with brown wood finish

Keep your boat's engine noise below deck!

Best sound deadening material for Boat Engine Compartment

The 2 best sound deadening products for a boat engine compartment are:

  1. Spectrum™ Spray On Deadener
  2. Damplifier Pro™ Sound Deadening Mats

The first which we highly recommend is Spectrum, which can either be sprayed or brushed on for a seamless, waterproof and rust-proof finish. Spectrum is a high heat viscoelastic polymer that sticks extremely well to a cleaned metal surface, and is easily applied with a spray gun, brush, or roller. Spectrum is the product of choice for boat engine rooms and any part of the boat experiencing heavy vibrations (like around a generator). Applying Spectrum will stop the compartment itself from rattling and transmitting structural noise, while modestly increasing the amount of noise blocked (more noticeable for lighter compartments). Spectrum also will prevent heat transfer. Most boat owners with a smaller boat go with Damplifier Pro, the peel and stick sound deadening material. With the mat product, make sure to seal the edges with foil tape to protect the material (pics below).

How to Soundproof and Add Boat Engine Compartment Insulation

Boat engines put out a lot of noise, over 100 decibels at a wide-open throttle for some vessels. If you’re ready to add soundproofing materials to that noise and insulate your engine compartment, here’s what to do.

  1. Prep the area.  Remove any materials that you want to replace - usually because it's decaying or ineffective. You’ll need to clean the surface of your engine compartment with denatured alcohol. There should be no debris, rust, or waxy oils.
  2. Apply sound deadener to the underside of the engine compartment. This is an upgrade over your existing setup and is OPTIONAL. Most of the noise generated by a boat engine is AIRBORNE (vs STRUCTURAL), so we want to cover 100% of the compartment to increase the density of the compartment as a barrier while also damping structural vibrations. Our testing shows using a vibration damper is most impactful if you have a smaller doghouse, because the tighter compartment construction tends to transmit more structural vibrations. For a larger engine compartment where you have more airspace and the engine is mounted, the vibration damping material will be most effective close to where the engine is mounted, although we often see people add damping material to the underside of the lid.
  3. You've reached the MONEY step - the TWO keys to a soundproofed boat engine compartment. There are two keys to dealing with the AIRBORNE sound waves coming out of your engine compartment.

(1) The compartment needs to be as airtight as possible. Sound is like water. It flows to the weakest point. And air gaps are VERY weak. If you can look at your engine compartment, and see clear openings - those must be addressed first. If you don't... you basically have a hole in your boat, and decided to invest in a fancy water pump to remove the water instead of plugging the hole. A well-designed engine compartment should cut the sound you hear from an engine putting out 100 dBs to 70-80 dBs.

(2) Add sound insulation material to the hard-surfaces of the compartment. Hard surfaces reflect sound waves. These echos build up, and increase the intensity of the sound inside the compartment. By absorbing this build-up, there's less sound pressure inside your engine compartment AND less sound escaping the walls. As a general rule, doubling the amount of sound absorbing in a space will get you a DB reduction of around 3 dB. This doesn't scale well, but can make a BIG difference in an engine compartment with minimal sound absorption. By adding sound absorbing and soundproofing materials to all the hard, reflecting surfaces in your compartment, you can cut the noise level by 6-10 dBs.

But what materials to use? Fortunately, we've got you covered no matter how your compartment is constructed.

Steps to Soundproof & Insulate a Boat Doghouse

    1. Add Sound Deadener - Completely cover the boat doghouse interior with Damplifier Pro.
    2. Seal the Seams - Tape the seams with foil tape to protect edges and seams.
    3. Add the Insulation - Your second layer is Heat Wave Pro, which adds insulation and sound absorption. It's very flexible for curved surfaces.
    4. Get out on the Water - Get that boat back out on the water! That's the smile of a man with a quiet boat!! :)

If your engine compartment is mostly curved surfaces, Heat Wave Pro is extremely flexible sound insulation and automotive heat insulation that can fit those contours. These all natural fibers (no itch) are treated to be water resistant (no mold or mildew) and durable. Two things to note about Heat Wave Pro is that it should be installed at least two inches away from the heat source and its edges should always be taped with foil insulation tape in marine applications. Heat Wave Pro and Damplifier Pro are combined in our Boat Insulation Kits.

Damplifier Pro installed in boat engine compartment

Step 1: Completely cover the boat doghouse interior with Damplifier Pro.

Tape the edges of Damplifier Pro - boat engine compartment

Step 2: Tape the seams with foil tape to protect edges and seams.

Heat Wave Pro inside the boat doghouse

Step 3: Your second layer is Heat Wave Pro, which adds insulation and sound absorption. It's very flexible for curved surfaces.

boat after soundproofing

Step 4: Get that boat back out on the water! That's the smile of a man with a quiet boat!! :)

Steps to Replace Sound Insulation in a Boat Engine Compartment

Before Starting - Evaluate the insulation you have. As boat engine compartment original insulation gets older, it can start to decay and fall off.

  1. Remove Insulation - Remove the old insulation to expose the metal (or fiberglass) underneath
  2. Clean the Area - Clean the application surface with denatured alcohol.
  3. Add Sound Deadener - Start with your vibration damping base layer. Damplifier Pro will stop any noise from structural vibrations transmitted through the engine compartment.
  4. Add Insulation - Install replacement sound and heat insulation. Mega Block's reinforced foil barrier layer redirects radiant heat. And then the hydrophobic melamine foam behind it absorbs sound waves and also reduces heat transfer.

If your engine compartment is mostly flat surfaces, you'll have an easier time with our peel and stick hydrophobic melamine foam. This is our top-of-the-line (aerospace grade) sound absorber and heat insulator. We have two versions. Mega Zorbe is just the open cell foam, and is perfect for anywhere you have at least a 6" air gap between the material and the engine. Mega Zorbe is 1/2" thick, but can be stacked for increased sound absorption. Mega Block is the same open cell foam, but it's covered by a 1000°F heat shield and our "go to" material inside a boat engine compartment, which allows you to install it with only a 2" air gap from the engine. We combine Damplifier Pro and Mega Block together in our Boat Insulation Kits.

boat insulation falling off

Before Starting: Evaluate the insulation you have. As boat engine compartment original insulation gets older, it can start to decay and fall off.

boat insulation close up

Here's a close up view of the jute insulation. As it has crusted over and become brittle, it's no longer absorbing noise.

old boat engine compartment insulation

One final shot of the other side of the engine compartment. We've got the full picture now.

engine compartment with old insulation removed

Step 1: Remove the old insulation to expose the metal (or fiberglass) underneath

Clean that engine compartment with denatured alcohol

Step 2: Clean the application surface with denatured alcohol.

Damplifier Pro installed in boat engine compartment

Step 3: Start with your vibration damping base layer. Damplifier Pro will stop any noise from structural vibrations transmitted through the engine compartment.

Mega Block installed in boat engine compartment

Step 4: Install replacement sound and heat insulation. Mega Block's reinforced foil barrier layer redirects radiant heat. And then the hydrophobic melamine foam behind it absorbs sound waves and also reduces heat transfer.

Mega Block cut around engine compartment hose

Make sure you leave space for any hoses or clips that need to be re-attached. The final step is to tape any seams with foil tape to help protect the material and extend its life span. Looking good!

Our best sound absorber. Install it on hard, reflective surfaces on your engine cover or in your engine compartment to reduce airborne sound waves

Replaces insulation inside a boat doghouse. Stops heat, absorbs sound, and resistant to mold and mildew.

Perfect for engine compartments with a flat surface. Hydrophobic melamine foam layer absorbs sound a 1000°F heat shield protects when you don't have much clearance

Boat... Meet Insulation. Insulation... This is Boat. You're Gonna Be Friends.

Your boat and this insulation are going to be best friends... they just don't know it yet. Get ready to introduce them. And introduce yourself to the peace of mind that comes from knowing you'll have the quietest boat at the dock.

  • Boat Doghouse Kit: Damplifier Pro ends that vibrational noise from the fiberglass housing. Then Heat Wave Pro cleans up with insulation and sound absorption. This kit was designed for anyone with a doghouse engine compartment on their boat that is looking for some noticeable noise reduction.

Get Help with Your Boat Insulation Project

Insulating your boat’s engine compartment is relatively simple and should take you no more than a few hours. No matter what materials you choose, remember to leave adequate ventilation and be careful not to cover any exhaust vents. As you know, on a boat, water gets everywhere.

The good news is you have options depending on your type of boat and your goals. Let us know if we can help you figure out the combination that works best for you, whether it’s thermal insulation or noise blocking.. And when you’ve completed your project, send us pics and helpful tips so we can continue improving our guides!

If you have any other problems with automotive or home soundproofing, check out our many other recommended posts! We have advice on how to reduce air conditioning noise, soundproof a room or office, and many more!

Have questions about your project?

Call us at 1.800.679.8511