rusty nail
Active Member
Has anyone spent time trying to make these boats quieter? Ie anything that could help, insulation under the rear hood, wrapping the mufflers with something?, any suggestions are welcome.
making 2 stroke sport boats quieter
- Thread starter rusty nail
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I think most of the noise is vibration, not engine or exhaust.
I have been working on my neighbor's 97 Challenger, I don't have a jet boat of my own. Fair warning, this is all theoretical, I have not been on a jet boat in the water yet. Still fixing one. This does work well in cars. A little Dynamat here and there works miracles, even on my old 84 Rabbit Convertible, which is LOUD with road noise.
The engine vibrates, and that sounds and vibration is transmitted to the hull through the motor mounts, which then cause the fiberglass to vibrate like a speaker cone.
To see how well any of this works, download a dB meter app and take before and after readings.
Step one is good motor mounts. OEM hard rubber is usually best in cars, poly usually doesn't dampen as well. Beats should be the same, I think there are just rubber bushings in the mounts.
There is a service bulletin about one of the mufflers getting loose and rattling against the hull. Not sure which boats off hand. Check that, and the muffler mounts. Metal-to-metal contact there would be very loud.
Next, I'd consider Dynamat on as many of the engine compartment surfaces as possible. It doesn't really have too have full coverage, as it isn't just a noise barrier, it absorbs vibration. This is best applied close to the source of the vibes, so the whole boat doesn't need sound damping.
The jet drive also causes vibration. Covering that hump with Dynamat may be very effective. It can be cut and applied in overlapping pieces that avoid all the hoses and cables.
A big square cut to fit each of the flat areas, including the bottom of the storage bin above the engine would help. Making sure the storage bin can't vibrate against the hull will help, too. Maybe some dense closed-cell foam rubber where the bin touches the hull?
Not sure how well Dynamat would stick to the fiberglass in the engine bay. It would have to be super clean. I know Dawn cleans very well, but in a car, I clean with alcohol next, which SHOULD be compatible with fiberglass, as we use it in circuit boards at work. I do know that acetone (nail polish remover) eats fiberglass on contact, so that is not the answer. Off-topic, acetone is also the top coat activator for NeverWet, so that shouldn't be used on boats, even though it sounds awesome for keeping the topside clean.
You could also apply some Dynamat to the back side of any hatches that open, so they don't vibrate and amplify the hull noises.
Header wrap for the exhaust cone might help as well, but I think that stuff absorbs water, so it may or may not be appropriate. Products vary. I have not personally used it, as even in cars it absorbs water and accelerates rusty pipes...if the are steel. Painted cast aluminum should tolerate it well.
Dynamat can be heavy, which is how it works. It adds mass to dampen vibrations, but used sparingly, with a bit on each large open panel, it will make a difference. You'll know how heavy by shipping weight, if you order online. Mercedes uses like a 12" x 8" piece stuck to the inside of the door panel to deaden vibration. That's enough to work there. West Coast Customs covers the whole floor when they do a custom car with an audio system.
I have been working on my neighbor's 97 Challenger, I don't have a jet boat of my own. Fair warning, this is all theoretical, I have not been on a jet boat in the water yet. Still fixing one. This does work well in cars. A little Dynamat here and there works miracles, even on my old 84 Rabbit Convertible, which is LOUD with road noise.
The engine vibrates, and that sounds and vibration is transmitted to the hull through the motor mounts, which then cause the fiberglass to vibrate like a speaker cone.
To see how well any of this works, download a dB meter app and take before and after readings.
Step one is good motor mounts. OEM hard rubber is usually best in cars, poly usually doesn't dampen as well. Beats should be the same, I think there are just rubber bushings in the mounts.
There is a service bulletin about one of the mufflers getting loose and rattling against the hull. Not sure which boats off hand. Check that, and the muffler mounts. Metal-to-metal contact there would be very loud.
Next, I'd consider Dynamat on as many of the engine compartment surfaces as possible. It doesn't really have too have full coverage, as it isn't just a noise barrier, it absorbs vibration. This is best applied close to the source of the vibes, so the whole boat doesn't need sound damping.
The jet drive also causes vibration. Covering that hump with Dynamat may be very effective. It can be cut and applied in overlapping pieces that avoid all the hoses and cables.
A big square cut to fit each of the flat areas, including the bottom of the storage bin above the engine would help. Making sure the storage bin can't vibrate against the hull will help, too. Maybe some dense closed-cell foam rubber where the bin touches the hull?
Not sure how well Dynamat would stick to the fiberglass in the engine bay. It would have to be super clean. I know Dawn cleans very well, but in a car, I clean with alcohol next, which SHOULD be compatible with fiberglass, as we use it in circuit boards at work. I do know that acetone (nail polish remover) eats fiberglass on contact, so that is not the answer. Off-topic, acetone is also the top coat activator for NeverWet, so that shouldn't be used on boats, even though it sounds awesome for keeping the topside clean.
You could also apply some Dynamat to the back side of any hatches that open, so they don't vibrate and amplify the hull noises.
Header wrap for the exhaust cone might help as well, but I think that stuff absorbs water, so it may or may not be appropriate. Products vary. I have not personally used it, as even in cars it absorbs water and accelerates rusty pipes...if the are steel. Painted cast aluminum should tolerate it well.
Dynamat can be heavy, which is how it works. It adds mass to dampen vibrations, but used sparingly, with a bit on each large open panel, it will make a difference. You'll know how heavy by shipping weight, if you order online. Mercedes uses like a 12" x 8" piece stuck to the inside of the door panel to deaden vibration. That's enough to work there. West Coast Customs covers the whole floor when they do a custom car with an audio system.
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