Making Outboards Quiet

[yachtorion]

My big objection to outboards is the horrid row they produce. Is there anything that can be done to make them a bit more diesel-noise level? Does foam in the cowling work? Are they actually the same volume and it's just the frequencies that are different and more annoying?

 

[Spyro]

I don't think foam in the cowling would make much difference. Seagul didn't even bother with one. Most of the noise comes from the exhaust.

 

[yachtorion]

I don't think foam in the cowling would make much difference. Seagul didn't even bother with one. Most of the noise comes from the exhaust.

I (naively it seems) thought the exhaust outlets were generally underwater and therefore well silenced?

 

[VicS]

My big objection to outboards is the horrid row they produce. Is there anything that can be done to make them a bit more diesel-noise level? Does foam in the cowling work? Are they actually the same volume and it's just the frequencies that are different and more annoying?

I would have thought that a small outboard was much quieter than a diesel engine. Perhaps its just that diesel engines tend to be in engine compartments with a good level of sound proofing.

Not all outboard have an air intake silencer fitting one would reduce the noise from that source. Sound insulation could, space permitting, be fitted inside the cowl . My 'rudes cowl is foam lined but I' d think proper sound insulation would be more effective. Although they do have resilient mountings maybe transmission of vibration through the clamp bracket could be reduced by further attention to the mounting onto the hull.

 

[C08]

I tried to reduce noise on a 30HP Tohatsu 2 stroke outboard by using quality 1" sound foam the type with a lead layer. I lined the cowl and the box that covered the outboard in its well and it made it made little difference. My current 20hp Tohatsu 4 stroke is much quieter so much so that I have to look at the rev counter to check it is running at anything below 3000 rpm!

 

[yachtorion]

I tried to reduce noise on a 30HP Tohatsu 2 stroke outboard by using quality 1" sound foam the type with a lead layer. I lined the cowl and the box that covered the outboard in its well and it made it made little difference. My current 20hp Tohatsu 4 stroke is much quieter so much so that I have to look at the rev counter to check it is running at anything below 3000 rpm!

Perhaps part of the answer is the 6hp on my old Hurley had to be worked pretty hard. A bigger engine running at less power might have been a lot quieter.

 

[RichardS]

My big objection to outboards is the horrid row they produce. Is there anything that can be done to make them a bit more diesel-noise level? Does foam in the cowling work? Are they actually the same volume and it's just the frequencies that are different and more annoying?

Outboards very considerably in noise level. If you avoid air cooled engines and stick to 4-strokes I don't find the noise particularly bad. It does vary from model to model though, even with 4T water-cooled.

Richard

 

[yachtorion]

Outboards very considerably in noise level. If you avoid air cooled engines and stick to 4-strokes I don't find the noise particularly bad. It does vary from model to model though, even with 4T water-cooled.

Richard

The outboard that put me off was a 2008 Mercury 6HP 4T

 

[FirstAway]

I used to have an 8HP Yamaha 2 stroke in a well on a Beneteau first 24; I did three things to quieten it down:

Against general advice I blocked the small exhaust vent at the top of the leg with sealant, it is apparently there to reduce the back pressure in order to make starting easier and idling more reliable - I never had a problem with either after I blocked the vent. This made a noticeable difference to the noise level.

In order to try and reduce the vibration I mounted the bracket on some rubber mountings. I didn't really notice much difference to the noise level.

I made an insulating cover to fit over the engine cowl, a huge reduction in noise, I did fear that the engine or carburettor might over heat, but in the North of England it turned out to be no problem.

Bob

 

[owen-cox]

I used to have an 8HP Yamaha 2 stroke in a well on a Beneteau first 24; I did three things to quieten it down:

Against general advice I blocked the small exhaust vent at the top of the leg with sealant, it is apparently there to reduce the back pressure in order to make starting easier and idling more reliable - I never had a problem with either after I blocked the vent. This made a noticeable difference to the noise level.

In order to try and reduce the vibration I mounted the bracket on some rubber mountings. I didn't really notice much difference to the noise level.

I made an insulating cover to fit over the engine cowl, a huge reduction in noise, I did fear that the engine or carburettor might over heat, but in the North of England it turned out to be no problem.

Bob

Sunsail used to have some beneteau 24s ( "baby Ben's" as they were affectionately named) with 2 stroke outboards in wells. they had a piece of copper pipe stuck up the above water exhaust and then connected to a hose that ran through the boat and out to a stern mounted skin fitting. they didnt seem to get too hot and they ran the fumes and noise out of the back which was a big improvement.

 

[PotatoNavigator]

In my experience the majority of the noise actually comes from the thing you've attached the outboard to. Mine is remarkably quite on a dinghy (Tohatsu 6hp sail pro), but makes a hell of a racket in the well of my boat.

 

[ianabc]

Smart phone app

Sound meter

shows the dB

level of many 30 to 50 hp ob

are very high

in fact in the hearing danger zone ! (90 dB)

 

[Spi D]

The noise experienced often is different to numbers on paper or measured dB, not least the frequenzy will decide.

Anything doing 4-6000 rpm will make noise so a bigger engine running lower rpm and lighter load is often the solution. At the same time bigger engines are water cooled, exchaust below water, commonly multi cylinder, less vibration and so on.

A real life test by a magazine shows differences between brands, but also instering is the noise vs speed increase: