Quietening a boat

[Simpo Two]

I have a 27' GRP cruiser with a Yanmar 3-cylinder 40hp diesel inboard. And frankly it starts to get rather wearing after a while. Noise comes from two places, the cockpit floor and the exhaust.

The cockpit floor has two hatches which account for about 70% of the flat space. They are GRP with wood reinforcement, approx 1" thick in the middle but thinner round the edges. They shut out a lot of the noise but not enough IMHO.

The exhaust is 75mm rubber hose with a Vetus gooseneck, and originally exited under the small bathing platform. In an effort to quieten the exhaust I extended the pipe to the edge of the platform and fitted a Vetus muffler www.vetus-shop.com/vetus-muffler-mp75-75mm-p-527.h... in the engine compartment. Extending the hose stopped the platform resonating but the muffler seems to have no effect at all.

I really would like to get the boat quieter, and welcome ideas

[Simpo Two]

I tried an oar, after the raw water inlet became clogged with weed courtesy of the EA. It wasn't a very satisfactory means of propulsion. Now, how to quieten a Yanmar...

[Simpo Two]

s2kjock said:

Have you room for sound-proofing foam panels under the cockpit floor?

I've looked at the various products available and in the end got so confused I gave up - too many options. Heat and fire aren't major problems I think as diesel isn't volatile and ventilation is out of the sides, not the floor. I understand that the type of noise to be stopped is important - this is a diesel operating at 1,000-2,400rpm.

s2kjock said:

Not sure about the exahust noise really - never a massive problem in boats I have sailed, although maybe just renewing aged/old fittings might make a difference in addition to the muffler?

It's a 2-year-old 3JH5E, so everything is effectively new. Other boats are quieter so it must be possible...!

[Simpo Two]

AlexIT said:

Do you have enough space to fit a waterlock?

We did on our boat and it made a massive difference, given that the original installation was basically a free flowing exhaust from the engine straight above water level.

Hmm, well I have the muffler and also a gooseneck (though I understand that's to stop water siphoning back into the boat rather than quietening). There isn't room for a waterlock as well - the so-called 'muffler' alone is about 2' long and despite having been recommended by Vitesse Marine seems to have been an entire waste of £160.

But it seems to me that all these boxes do is churn the exhaust/water mixture up a bit. Whatever happens in the middle, there is still exhaust and water exiting by a 75" tube at the back and that's what's making the noise...

Perhaps I should fit a waterlock instead of the muffler? It seems to do the job of a gooseneck as well...

[Simpo Two]

Thanks Alex.

I suspect one big grey box is much the same as another - gas and water go in, gas and water come out. Can't see how anything gets any quieter... just increases back pressure.

ETA: Thanks Mick, I'll drop them a line.

[Simpo Two]

XJSJohn said:

Remember, when fitting the sound insulation its not just teh underside of the cockpit sole that you need to be insulating, but the sides of the hull and bulkhead within the engine compartment, and sides of fuel tanks etc -

for the exhaust have you looked at having it exit under water?

Thanks John - the engine bay has large compartments on either side which are partly insulated with about an inch of black foam, but whether it's the right sort or sufficient I can't know. Some boats do have the exhaust exiting underwater but a 40hp Yanmar and a 3" pipe makes a surprising amount of gas - it would look like a giant fart! - but more importantly I'd be unable to check the cooling water exit, and that's not a risk I'd be happy taking. Unless I go for the separator mentioned above. What I'd really like is for an expert to look at it and tell me what's needed, rather than me just guessing and spending £££ on stuff that doesn't work!

[Simpo Two]

Yep, on each side of the engine and the forward bulkhead too. Shetland say they use Yanmar as they're quieter than Vetus - god knows what a Vetus sounds like!

[Simpo Two]

MOTORVATOR said:

Taking all mine out Simpo. Just done a journey to Guernsey and back and couldn't hear the Detroits for the incessant nattering coming from the wife.

So two options open to you. Have the old sound deadening material or the wife whichever suits.

Interesting! PM with details - many thanks

[Simpo Two]

I'd prefer clean bits to be honest - something to put under the engine hatches for starters as that's where the onboard noise seems to be coming from.

Any suggestions on the exhaust please?

[Simpo Two]

XJSJohn said:

seriously though - shouldn't be that much noise coming from the exhaust though .... you have one of them brown vetus exhaust baffle thingies ......

It's a big grey plastic oval section box, but there was no difference that I could tell before and after fitting it. The issue as I see it is that there's a 3" diameter hole with large amounts of gas and water farting out!

The funny thing about boats is this. If it was a car, you could take it to a bloke and say 'Here is some money, fix it' and they would. With boats there seems to be no such infrastructure, at last not inland.

[Simpo Two]

^^ That's the one. There's also the large gooseneck I mentioned, mounted inside the transom - another grey plastic box filled with water and gas! Is one grey box better than another? I'm thinking there should be something on the end of the hose to diffuse the exit...

And why would Vitesse have recommended a baffle if a waterlock is better?

I think I'll contact Halyard and send them some photos and see what they say.