My boat sounds like a lorry - exhaust advice please

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mikeakc

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As per the title, my BMC 2.2 runs fine but on a long run it starts to feel like I'm driving a luton van up the A30. I plan to install some sound deadening in the engine box to reduce this but still, I listen with envy when I hear the put-put of old fishing boats go past. The difference could be summarised as follows. Mine creates constant rpm sound just above idle whereas the charming fishing boats have a muffled, inconsistent gurgling sound. I assume this is caused by exhaust gas building up enough pressure to kick water out of the pipe. Could anyone advise how to arrange things to make the boat sound nicer? I ask as I'll be faffing around taking the floor up over the exhaust at the end of the season, and if this is a relatively simple 'change the muffler' solution then I might do so. If the answer is 'change the engine' then I might leave it.
Thanks in advance for entertaining such an unnecessary and whimsical project.
Mike
 
As you don't say what the exhaust system consists of it is difficult to make any suggestions. However they are mechanically noisy engines. Do not be deceived by passing boats seeming quiet - they may be to you but you are not on them!

In general a proper waterlock installed correctly significantly reduces exhaust noise because of the water in the system. You can also add a second silencer although normally just the waterlock is sufficient. The other 2 sources of noise are intake roar which can be reduced by sound deadening and vibration particularly if mounts are hard and engine not allowed to move independently of the shaft.
 
There's a big difference in installation location / boxing between a fishing boat and a typical yacht.

Also that many such commercials have Low Speed Diesels ..... with large high thrust low rpm props. Your average yacht has a higher rpm, smaller prop to avoid drag.
 
mikeakc said:
As per the title, my BMC 2.2 runs fine but on a long run it starts to feel like I'm driving a luton van up the A30. I plan to install some sound deadening in the engine box to reduce this but still, I listen with envy when I hear the put-put of old fishing boats go past. The difference could be summarised as follows. Mine creates constant rpm sound just above idle whereas the charming fishing boats have a muffled, inconsistent gurgling sound. I assume this is caused by exhaust gas building up enough pressure to kick water out of the pipe. Could anyone advise how to arrange things to make the boat sound nicer? I ask as I'll be faffing around taking the floor up over the exhaust at the end of the season, and if this is a relatively simple 'change the muffler' solution then I might do so. If the answer is 'change the engine' then I might leave it.
Thanks in advance for entertaining such an unnecessary and whimsical project.
Mike
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What size/type boat is it & as Tranona said do you have filter/silencer on intake ?
Jim
 
It's a Colvic Northerner 26'. I'm not sure what the exact exhaust setup is at the moment but will photograph it and report back. Thanks for the feedback so far!
 
You should also check the amount of water coming out of the exhaust. If there is not sufficient, this will make the waterlock less effective. If the engine has a heat exchanger built in, then this could need cleaning.
 
Here is the current setup. Pretty sure the heat exchanger is fine as I cleaned it this winter. Any thoughts on this setup? Mufflerbox Nell.jpeg
 
mikeakc said:
Here is the current setup. Pretty sure the heat exchanger is fine as I cleaned it this winter. Any thoughts on this setup? View attachment 138578
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That home made stainless box looks like a good sound amplifier ! I would start by fitting a Vetus water trap/silencer - one on ebay at the moment.Length of the pipe is a big factor in sound deadening in wet exhaust systems.You seem to have plenty of room in the keel then up & out as existing.
Jim
 
bristoljim said:
That home made stainless box looks like a good sound amplifier ! I would start by fitting a Vetus water trap/silencer - one on ebay at the moment.Length of the pipe is a big factor in sound deadening in wet exhaust systems.You seem to have plenty of room in the keel then up & out as existing.
Jim
Click to expand...

My mates 1GM10 has a metal pot silencer similar .... makes it the loudest POP POP I ever heard !!
 
Our Beta 50 runs through a factory (1989 Jeanneau) stainless waterlock - a fair bit bigger than above, but otherwise looks very similar - but it sounds great! I like the throaty exhaust note with our 4 pot. Plus it'll never melt!
 
Not a good setup for the reasons suggested and also shows signs of the usual corrosion at the welds. To fit a Verus type you need a minimum 30cm fall from the exhaust elbow to the waterlock and a swan neck at the transom. There are different shapes of waterlocks so you need to work out the whole system ro decide on the nest type and where to position it.
 
The black version of the vetus NLP water locks would fit in place of the one you have I think. It’s more durable (and expensive ) than the grey ones. But they are pretty effective at reducing exhaust noise as they are dual chamber type.
 
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