Silencing the speedster!

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To2d

To2d

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I have a 99 speedster SK and love it! My family loves it!
We all love it except when we are trying to have a conversation with a buddy on his boat and mine is running. Its a loud boat witch I'm fine with but a little quieter at low speed and idle would be nice.
I looked into sound suppression mats like Dynamat and hush mat and I think this is a great way to start.
I reached out to Dynamat and told them what I want to do. I sent them a cut away of the back of the boat from parts supplier and asked " is it best to apply you product to the access tray that directly covers over the engines OR apply to the pop up engine cover over the access tray"? They said engine cover but didn't sound to sure or give a reason.
Has anyone done this and how did it work? And ideas on the best place to apply the mat?
 
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1) Re-duct your engine compartment ventilation system by adding a "U" shape to the interior section of the ducting. Make sure to put sound dampening material on the inside of the new ducting.

2) Insert some tubing into the exhaust ports that have a bend in it, to vent the exhaust further under water. Consider adding a "gun silencer" type baffle to the end of the tubing. Tubing that is not smooth will work better for noise reduction.

3) Add more material around the air intakes, such a small vented box with noise dampening materials inside.

4) Build a large "shield" that will loosely cover the motors. Not a blanket, but more of a "car port" type of thing, with noise dampening material on BOTH sides.

5) Ensure that nothing is touching the motor or exhaust, as the vibration will travel strait into the hull and make a lot of noise.

6) Ensure that all the rubber mounts for the motor and exhaust are not worn out, allowing vibrations to travel.

7) Check the engine hood gasket, and try to make improvements there for a better seal.

8) add noise dampening material to the under side of the engine hood.

9) check out the drive shafts, any excess play that could be transmitting vibrations to the hull?

10) add a "spoiler" that would separate the seating area from the engine compartment and exhaust. (make it flexible and or retractable)

11) add a spoiler to the very rear of the boat, to block the exhaust sounds from coming forward. (make it flexible and or retractable)
 
Number 8) is what I'm interested in! Is the engine hood the best or the access tray that is between the engines and the cover? Thats my question
 
I'm interested but skeptical at how effective Dynamat on the hood or tray would be. I would think the majority of the noise would be exhaust or from engine bay vents. I've run my boat with the tray out (hood closed) and it didn't seem to affect the noise level much. Adding another layer there, even if it is sound deadening material, might be redundant.

In any case, please post pictures/results if you give it a go.
 
you mentioned "Re-duct your engine compartment ventilation system by adding a "U" shape to the interior section of the ducting. Make sure to put sound dampening material on the inside of the new ducting."

i am having a hard time visualizing this...

Can you draw out your idea or go into more detail?

After doing some more reading it looks like that is another great place to look. The ports already have some sound deadening right at the exit point but it seams to not be enough "or is too old to still work"
 
basicly I think it is a 4" duct grab a piece of 6" piping alum or plastic and line the inside with the same rough black foam that is on the bottom of the engine cover. Place a 90 on the engine bay vent and then mount the muffler there.

Im in the same boat I think my sportster 951 is loud with the air arrestors on it and the hood down.
 
Jdmcrx... What??? Move the muffler? I have two engines and doing the mod your talking about is impossible on my boat. I am just trying to silence the engine noise coming through the engine bay vents. "one on each side of the boat. "
 
You are correct JD, its just a "U" shaped piece of tubing with noise dampening material inside of it. Then look inside your engine compartment and examine the ventilation system. There is a round tube for the inlet and a round tube for the outlet. You would attach this "U" to the ventilation tube on the inside of the engine compartment. Noise mainly travels in a line of sight. The "U" eliminates the line of sight. The noise dampening material in the "U" will cut down on the amount of sound that will ricochet around inside the "U". Im not sure how else to explain it.
 
Perfect ... I now get it. Sorry I am a visual guy and need to look at it while I read that.
Now I just need a sunny day with nothing to do!
I still also want to try the sound pads on the cover and tray
 
To2d

I mean the engine compartment fresh air duct ! Is it the exhaust that's loud or the engine compartment ? My sportster is the engine compartment that's loud .

To2d said:
Perfect ... I now get it. Sorry I am a visual guy and need to look at it while I read that.
Now I just need a sunny day with nothing to do!
I still also want to try the sound pads on the cover and tray
Click to expand...
 
Exhaust is not the issue...The engine compartment noise at low speed or above idle is.

My goal is to lower the Noise coming from the engine compartment
 
Here is a test I did with a sound Db meter.
271.jpg

*The first picture is just the standard out door noise and engines off.
*The second is with towels wrapped around the engine air ports both engine running.
*The third is the how it always is loudq with both engines running.
*The last shows the placement of the Db meter and that it didn't move.
Now all of these were done out of water so it was louder but you can tell that the engine ports are a great place to start on silencing .
The right side doesn't even have a blower. It's just an empty hole to the loud engine bay.
272.jpg
I need to find a good way to limit sound and still allow air flow.
 
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That's a nice tool to have. I'm pretty sure that if you attach a 10 foot dryer vent hose to the intake and exhaust ports of the engine bay venting tubes, you will have good results. Wrap noise dampening material around the first 2 feet of the hose that attaches to the vent tubes, and then make several bends in the tube and zip tie it where ya want it. You could even put an "airbox" on the end of the tube, with inner baffles to cut down on the noise even further.




dryer-vent-types.jpg
 
P.S. the empty hole you speak of is the intake for the ventilation system, otherwise there would be a slight vacuum in the engine bay that would not agree with the performance of the engines. The other side is the exhaust. Just like a PVC setup on an old truck engine >> both valve covers have vents. One is intake, one is exhaust - which - is through the PCV, and into the manifold. Anyway, just think intake and exhaust.
 
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You could also explore some materials to wrap the water boxes and the second set of mufflers if your boat has them. The exhaust is supposed to flow better the hotter it is as well :cheers:
 
snikwad003 said:
You could also explore some materials to wrap the water boxes and the second set of mufflers if your boat has them. The exhaust is supposed to flow better the hotter it is as well :cheers:
Click to expand...


Hmm. What could he use to insulate the exhaust. It would have to be waterproof - which rules out most conventional insulation materials such, as R13 insulation or woven fibers. If the temperature stays low enough, he could use expanding foam. The foam would definitely hold the heat in, increase buoyancy, and reduce the DB's a bit. If the temps are too high, you would have one hell of an engine fire though. Lets light the entire exhaust system on fire, ventilate it with the bilge fan, and then put a plastic gas tank 3 inches away. That would be one wild ride.
 
Yeah what ever goes in there that lowers the DBs will probably absorb water and eventually smell terrible. Except for the water absorbent part of every day house insulation, it would probably work good. Certan insulations are flamable only because of the glue and the backing that is glued onto the fiberglass, not the insulation its self. Just what non flamable waterproof flexible insulation is avalible?
 
I guess he could just 'fiberglass' the exhaust. With the cans of resin and fiberglass matting. It would definitely be waterproof, and would provide moderate noise and heat insulation. It would look too, if done properly.
 
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