Reducing outboard engine noise

Vid

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I have an Achilles 24 with a Mercury 6hp 4-stroke engine sitting in a well in the cockpit. It's a very convenient set up in many ways but it is a noisy noise, particularly if you have to motor for a few hours on passage, or along a picturesque river for example.

I'd like to reduce the noise if I can - one idea I have is to construct some form of foam-filled "hat" that would sit on top of the cowling, but a) I don't know if this would reduce the noise and b) whether it would interfere with the operation of the engine, eg by causing it to overheat through reducing air cooling or affecting the exhaust.

Has anyone got any thoughts or suggestions on an effective noise-reduction solution I could take, short of going before the mast and letting the autohelm do the work.

Many thanks.
 

Tranona

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Doubt there is anything you can do. Just a characteristic of that type of installation. You need it open at the top to allow the engine to breathe. If you cover it up you will probably starve the engine of air and have a build up of exhaust fumes. Might be worth experimenting with some panels of foam to make a temporary cover, but noise insulation relies on shutting off all paths which effectively means making it airtight so leading to the potential problems already mentioned.
 

Lakesailor

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Instead of stuggling to achieve a result with your idea, just spend a few quid on an outboard bracket and solve the problem, like these blokes.

(keep the one in the well, as well, if you fear the stern mounted one won't work in a sea)





 
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William_H

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I have always had my O/b on a bracket on the transom. It does get the engine another metrre away from your ears. Also frees up more space in the cockpit. With an adjustable height bracket I have never had problems in big waves trying to keep the LS in the water.
The only thing I know tro reduce O/b noise is to have a twin cylinder engine which is a lot smoother thna single cylinder. good luck olewill
 

Vid

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Well, that is a solution that I shall look into, and it would have the advantage of then being able to lift the engine out of the water whilst sailing, though I was thinking of fitting a boarding ladder to the stern.

However, I was hoping that simply by wrapping some foam around the cowling that it would help - has anyone tried anything as simple as that?
 
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Lakesailor

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Loads of people have tried. It's just not going to do the trick.
I am always sceptical of the 2 cylinders better than 1 theory as well.
It depends what pitch you find annoying.
I prefer the lower pitched thump of a 4 stroke single to the high pitched whine of a 2 stroke twin.
 

lw395

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One thing you could try is to put some rubber between the outboard clamp and whatever it clamps to.
You want something fairly dense and perhaps 3 to 6mm thick?

But that noise should be telling you 'sail don't motor'.
When a motor is needed, you'll not notice the noise.
 

VicS

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Well, that is a solution that I shall look into, and it would have the advantage of then being able to lift the engine out of the water whilst sailing, though I was thinking of fitting a boarding ladder to the stern.

However, I was hoping that simply by wrapping some foam around the cowling that it would help - has anyone tried anything as simple as that?
Troubles with outboards on brackets:

Tend to lift the prop out of the water when pitching, unless long or extra long shaft fitted. ( this may mean the same engine is not ideally suited for bracket or well mounting)

Prop behind, or to the side of, rudder so no wash off the rudder to aid manoeuvring.

Controls difficult/awkward to reach unless extended or remote.

Difficult to lift on and off bracket unless as strong as a gorilla with arms as long as an orangutan's and a back as strong as an ox's.



Ordinary foam unlikely to have any significant effect. It you are going to try any sound proofing use proper sound absorbing or deadening materials.
 

penfold

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Does the well not have a lid? Would it be possible to construct one? It will need a vent, to the aft face is probably best; the vent will have to be convoluted to block direct noise transmission and lined with absorbant sandwich, as will the rest of the lid, and the upper parts of the well too if possible. The well on the Impala I sail on keeps the sound down with the lid on but unfortunately the engine chokes on its own fumes so you have to run with the lid open and lots of noise; I did sketch up a ventilation scheme but the owner has other priorities! If you could keep the lid shut and the well was insulated with absorbant sandwich it would probably be less noisy than most inboards.
 
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FirstAway

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I have a First 24 with an 8 HP 2 stroke Yamaha in a covered well but no front panel. I thought that most of the noise was coming from vibration through the mounting bracket, so I fitted some rubber mountings on the bracket with no noticeable improvement. I then tried lining the inside of the well with thinsulate, again just a marginal improvement. So finally I tried as you are suggesting making a thinsulate hat to fit over the top of the engine, it is obviously not all encompassing as you need cut outs to get to the controls and starter cord, and there is enough free area at the base to allow sufficient air in. I was worried about it getting too hot but in the North of England that does not appear to be a problem as it has been running like that for several years now. And yes it made a significant difference to the noise level, still not peaceful but no longer painful.
 

Vid

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Firstaway - many thanks, some encouragement there to think I'm not completely on the wrong track here.

Interesting that you used Thinsulate, which I associate with warm clothing in cold weather rather than noise insulation.

My Mercury outboard has a black cover and it is just this that I am thinking of insulating, so I would not be changing the environment of the engine in the cockpit well, apart from thickening the existing cover, so will not be changing air supply or exhaust gases and obviously the controls will remain accessible.

I think I will experiment with some form of hat for the engine - it won't be expensive or require boat modifications and if it just takes the edge off the noise it will be an improvement.

Any other suggestions for suitable noise abatement material?
 

dylanwinter

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Firstaway - many thanks, some encouragement there to think I'm not completely on the wrong track here.

Interesting that you used Thinsulate, which I associate with warm clothing in cold weather rather than noise insulation.

My Mercury outboard has a black cover and it is just this that I am thinking of insulating, so I would not be changing the environment of the engine in the cockpit well, apart from thickening the existing cover, so will not be changing air supply or exhaust gases and obviously the controls will remain accessible.

I think I will experiment with some form of hat for the engine - it won't be expensive or require boat modifications and if it just takes the edge off the noise it will be an improvement.

Any other suggestions for suitable noise abatement material?
Just for experimental purposes I put a puyffa jacket over the outboard

I reckon that it did reduce the noise

certainly the higher frequencies

so this winter I am planning to make a giant tea cosy that will double as a seat

I am on the look-out for a tatty but well padded anorak

might even use the zip in some way

D
 

Billows

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Are there not electronic noise cancelers? It outputs a noise with a waveform which cancels the noise waveform. Anyone tried these?
 

duncan99210

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Back when we had a mobo powered by a 70hp outboard, the lid of the outboard came lined with the same sort of stuff as lines my engine space on Rampage - a sort of dense foam rubber. It cut down the noise for the engine quite markedly. I se no reason why you could not use a similar sort of material to make an external "hat" for your outboard provided it did not impede any airways into the engine lock.
 

paul.norton

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For outboards in engine wells, some owners have an extra pipe installed in the upper part of the engine leg which ducts the exhaust through the transom.

This allows a cover to be closed over the engine and prevents it suffocating on its own fumes. Obviously the well still has to be ventilated.

Paul
 

woozy-UK

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my 5hp honda outboard is transom mounted on my intro. when we grounded it cracked the aluminium lifting bracket. so we fitted a new steel lifting bracket... much more vibration than before. very annoying as we had to drill holes in different locations for it
 

Even Chance

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my 5hp honda outboard is transom mounted on my intro. when we grounded it cracked the aluminium lifting bracket. so we fitted a new steel lifting bracket... much more vibration than before. very annoying as we had to drill holes in different locations for it
I changed my E-Boat transom mount this year from an old Seagull fixed one, to a lifting aluminium one, and the vibration has reduced considerably. Im also now using a 2 cylinder 8hp which is also quieter and smoother. Far better on both counts...
 

FirstAway

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I read somewhere that thinsulate was good at noise as well as heat insulation, it may have been an article in PBO? It is also very easy to work with, just a pair of scissors and some adhesive tape. It is falling apart now but must be five years old.

The other thing that had a noticeable effect was to block the high level exhaust outlet, many would say that this is not good practise as it leads to starting problems, but I just increased the idle speed slightly and have had no problems. To be honest I did this initially because the engine is in a covered well and it used to suffocate on its own exhaust if running slowly. I experimented initially with just taping over the holes but after it ran without problems I just filled them with a bit of epoxy.
 
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