Hitting the water on the weekends is an extremely relaxing exercise, unless of course you have a noisy engine. If that’s the case, it’s a constant assault on your ears and due to sound travelling further across water it is also an assault on the ears of anybody unfortunate enough to be close to you.

Boat engine noise is definitely one of the disadvantages of owning a boat, but I can help you with a method you can use if you want to know how to soundproof a boat engine cheaply.

This guide aims to give a few tips on how to reduce the sound coming from your engine. I will be honest with you though, you are never going to completely eliminate all boat engine noise, it is simply impossible.

However, you can reduce it to a manageable level using the tips laid out in this guide.

Below are two guides for soundproofing a boat engine. Firstly for outboard motors, and then secondly for inboard motors, so scroll down depending on what you need.

Soundproofing Outboard Motors

Let’s focus on the actual engine noise. Most boat engines have a cover over the actual engine, this is called the cowling and is usually made of thin fiberglass. Soundproofing an outboard motor is a bit trickier than an inboard motor but you can still shave off a significant number of decibels.

Step 1: Install Insulation in Cowling

You can purchase some closed cell polyurethane insulation with an aluminum backing to protect the foam from fuel, grease and heat and stick it to the inside of the cowling. The stuff I prefer to use is the Uxcell product on Amazon.

This will work reasonably well, but foam will only go so far, as it will typically only eliminate high frequency sounds. If you want to eliminate the low frequency sounds you will need to use a dense and flexible material like Mass Loaded Vinyl (MVL), this is a type of nylon that contains Barium Sulfate to increase its density. I swear by this Stinger product.

When fitting the material, make sure your material covers as much of the inner cowling as possible without obstructing any air vents or coming into contact with any moving parts.

Having the air vents open means that sound will still escape but overall you will have improved the noise levels. Adding rubber gaskets between your boat and the engine might have a small effect, however it’s not generally worth the effort.

Step 2: Install Insulation on Cowling

If you don’t mind your engine looking rather ugly then you can even cover the outer surface of the cowling.

A good way of doing this is to buy a premade cowing cover (see on Amazon). This will be designed to fit your specific motor and it won’t cover any air vents. They also look better than anything you could cobble together over the weekend.

Although not specifically designed for sound insulation they have been reported to reduce sound levels significantly so will help the overall process of making the boat engine quieter.

Soundproofing Inboard Motors

Inboard motors are a lot easier to insulate as they are already enclosed. This makes it easier to isolate the sound.

Step 1: Install Rubber Matting

The first thing you can do is add rubber matting. I love this stuff on Amazon from Rubber-Cal. Fit it under your engine or by using rubber mounting feet.

It will help to remove a lot of the vibration between the motor and the boat. The vibrations will turn your boat into a drum and you will hear the sound anywhere in the boat.

Step 2: Install Insulation

You can then line the inside of the motor enclosure with similar sound deadening materials that eliminate both high and low frequency sounds such as Mass Loaded Vinyl (see TMS on Amazon) – stick it to the motor enclosure walls.

You will get the best soundproofing results by using insulation panels that have an adhesive on the one side as this will make installation easier.

If you cannot find these types of panels then get some green glue to stick the panels and be sure to over any exposed areas as any gap will reduce the overall effectiveness of the insulation. You should also use mylar tape to cover all the corners and edges.

By using a soundproofing material that is heat rated with an aluminum backing, it will protect the sound insulation from fuel and oil. You will typically have more space inside this enclosure, so you can add more insulation to further reduce the sound generated.

As in the case of the outboard motor, you can also upgrade the muffler of the engine as the exhaust for an inboard motor is also on the outside of the boat.

Final Thoughts

Many long-time boaters claim that they enjoy the sound their boats make, but this is often due to them suffering from mild hearing loss over the years as a result of being constantly next to a loud engine. Their engines are not nearly as noisy to them as they are to everybody else. To escape a similar fate, take the time to soundproof your boat engine.

What Causes Boat Engine Noise?

Any combustion engine generates a lot of noise, this is a fact. These engines are basically controlled explosions and as such noise is created through the resulting vibrations, the exhaust and the actual propeller in the water.