Why is my boat engine so noisy?

Rivers & creeks

Rivers & creeks

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We have a Mini Clubman diesel, about 98hp. You could stand and chat in a whisper next to it, from cold you can hear leaves rustling in nearby tress and children inside asking why we haven't set off yet.

The 75hp Thornycroft on The Kipper is in a wooden engine room lined (almost) throughout with pukka absorbent stuff; but you can't hear yourself think in there at tickover and in the wheelhouse it's just noisy, a blessed relief when it's turned off. No bad noises or knocking or stuff, just buckets of engine noise. It's 25% lower power, much lower revs but makes 10 times the noise - why?

It doesn't have any sort of air filter though, just a metal gauze to stop pigeons getting into the cylinders but it does have a nice water cooled exhaust and it's own insulated room on the boat. It's 1977 but is its age really to blame?
 
Almost certainly your Thornycroft will be a direct injection diesel. This coupled with the design of the injector system and combustion chamber shape means that a significant part of the fuel injected 'explodes' giving you the characteristic 'knock' of an older diesel of this type.

Modern diesel design has reduced the 'knock' to near zero. This coupled with careful attention to noise paths makes modern diesels the quiet little animals they are.

BTW my Perkins 154 is just about as noisy for the same reasons.
 
Long stroke engines are very noisy and lack of "proper" sound insulation all around as well as sound from the exhaust and perhaps the echoing of the sound from the hull directly below; it all adds up. But I bet it is not as noisy as my 28hp Volvo MD11C
 
Lazy Kipper,

When you are as old as me and your hearing is fading it won't be such a problem.

I can hardly hear my Thornycroft T80. I have to check the gauges to make sure it's running.:encouragement:
 
the engine is bolted to an extremely solid structure (your CW has a hull almost an inch thick) and in effect you have a 55KW loudspeaker.
 
TQA said:
Almost certainly your Thornycroft will be a direct injection diesel. This coupled with the design of the injector system and combustion chamber shape means that a significant part of the fuel injected 'explodes' giving you the characteristic 'knock' of an older diesel of this type.

Modern diesel design has reduced the 'knock' to near zero. This coupled with careful attention to noise paths makes modern diesels the quiet little animals they are.

BTW my Perkins 154 is just about as noisy for the same reasons.
Click to expand...

{pedant hat} surely indirect, that is, injector sprays into pre-combustion chamber? I thought Thorneycrofts were based on BMC designs.
Apart from that, all the suggestions are contributing.
 
My Car and Boat are close in power terms:

Mercedes E220 CDi (2.15 litre Twin turbo 170bhp)

Volvo Penta TAMD40b (3.7 litre turbo 165bhp)

In fairness, the Volvo's are very sweet, and economical, but heavy and take up a chunk of space!

The Mercedes can be tweaked reliably up to 220bhp, I suspect the old Volvos would be capable of more with Superchargers....(and probably were later on in development!)

I'll bet those big old Diesels will do more hours though, even with modern oils and technology!
 
If you took your Mini engine out of its car you would be surprised how much noise it makes. The refinement is mostly in the installation. Although your boat engine is inherently noisy owing to its design, but it is housed in a big soundbox which amplifies the noise rather than suppresses or absorbs it.
 
I have a fifty year old petter 12 horse power. It's bigger than my car and noisier than a train. But I do love it
 
My 1973 Volvo MD2b rattled everything in the boat, including your teeth. You didn't just hear it, you felt it, experienced it. Even the exhaust came out as a series of distinct explosions despite the water trap silencer. You could hear it coming from half a mile away I was told.

My 2008 Yanmar 3ym30 has one more cylinder (I wonder if each is offset at 120 deg?) revs faster and generates 25% more power. Yet it is as smooth as a baby's bottom, Dockside observers often comment that they cannot hear it running as I glide by, NOTHING rattles inside the boat, I can tell it is running, but it is in no way obtrusive. It is still a pleasure to turn it off when the sails start to pull, but running it all day & night would not be a problem.

Yes, engines have certainly come a long way in 35 years.
 
Interesting - I replaced my BMC 1.5 Thornycroft diesel with a Beta 25hp. I replaced the sound insulation with the latest best insulation but was dissapointed as the Beta is noisier than th BMC! The bmc you could hardly hear it when idling whereas the beta is far noisier. BUT the Beta is very reliable and I live with the noisier idling......
 
Millions will probably have been spent optimising the NVH (Noise, Vibration and harshness) on your Mini. As people has said, modern diesels inject the fuel in a very different way to it doesn't "knock" like an old boat engine does. The positions of the mountings will have been selected so that they're as close as possible to antinodes (areas where the vibrations in the engine block or gearbox are smallest) so that they feed less noise into the car's frame (and the subframe itself on to which the engine mounts might be rubber-mounted to the car). The design of the engine mountings (their angle and stiffness) will have been optimised too. Your boat engine probably sits on four very hard rubber "lumps" positions anywhere that was convenient. The car engine will almost certainly have a tricky dual-mass flywheel - and quite probably, a crank damper. to further reduce vibration. Lastly, the connection from the gearbox to the driving wheels will probably be flexibly jointed and the wheels themselves connected to the car's structure by rubber bushes. Is you gearbox connected rigidly to your propshaft on the boat? IF so, a flexible drive (like the Halyard ones) will help reduce te amount of vibration transmitted to the boat structure (which then reverberates round and makes more noise inside the boat). One big improvement I made on ours (horrible single cylinder 12HP) was to fit some Vetus hydraulic engine mounts to dampen some of the vibration from the engine before it got fed into the structure.
 
I knew what to expect with engine noise when I bought my present boat fitted with a Thornycroft engine as in the 1970's I sold BMC vans (BMC J4) fitted with this BMC Diesel engine, and what made it worse with these vans was that the engine was located between the seats and even with the lid down you had difficulty in having a conversation
On my boat an attempt has been made to cut down engine noise as the engine hatch is solid 2" Timber and stuck underneath is 2" soundproofing.
I would like to make the boat quieter and have noticed that no attempt has been made to stick soundproofing to the underneath of the cockpit floor and that is what I may do.
I also remember that you could buy an Aluminium Rocker Cover which when fitted cut down the engine noise as the normal "Tin" Rocker cover lets all the noise through.
 
TQA said:
Almost certainly your Thornycroft will be a direct injection diesel. This coupled with the design of the injector system and combustion chamber shape means that a significant part of the fuel injected 'explodes' giving you the characteristic 'knock' of an older diesel of this type.

Modern diesel design has reduced the 'knock' to near zero. This coupled with careful attention to noise paths makes modern diesels the quiet little animals they are.

BTW my Perkins 154 is just about as noisy for the same reasons.
Click to expand...

Maybe you've confused direct and indirect injection with common-rail? Nearly all diesels of the design date of the BMC diesel were indirect injection with mechanical injection. ie injection into a pre-combustion chamber. The Thornycroft was BMC-based and indirectly injected.

Nearly all modern diesel engines are direct injection (VW normally aspirated models have the SDI suffix) which gives far greater efficiency, better combustion and less pollution. Add to that the enormous benefits offered by a compressor (turbo-charger) to fuel-particle size, charge-mix and temperature and you've about x2 the power output for the same fuel consumption and about 50% of low-frequency noise. Listen to a normally aspirated diesel and it's pre-compressor alternative (Peugeot or VW) and you'll notice the noise difference.
Ironically there are few direct-injection small marine diesels, excluding road-vehicle derivatives being produced, even now and no common rail.
To answer the OP's question, in one word "progress". His BMC based mill is surely less noisy than the old Ford cast-block! So he has something t be thankful for.
 
The BMC 2.2 diesel in my motorsailer is very noisy, despite being in a box that has decent acoustic material on four/five sides. A lot of the noise seems to be low down, i.e. crankcase/pistons rather than top end combustion noise. It is possible to buy acoustic blankets that are supposedly effective. I have spoken to these people http://www.noisekiller.co.uk/ who seem knowledgeable, they can supply blankets with all the ports, flaps etc. that you need to accommodate all the ancillary bits.
A PM to Elessar might be useful, he was a dealer for one of the manufacturers.
Googling 'engine sound deadening' brings up many hits.
 
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