Engine soundproofing: observations and questions

[Greenheart]

Boatshed. Great little website, that...pick a boat you're interested in, Google the name with 'boatshed', and usually, you'll find forty or fifty photographs of the exterior/interior. Including under-floor shots of the oily old diesel, neglected or otherwise...

...but what these pictures mainly show me, is that the closest most boat-builders or owners come to silencing their engines, is enclosing them in a compartment. You don't often see mountings that diminish vibration, or foam-lined walls to muffle the machinery's volume.

Meanwhile, on Youtube, one often sees footage of sailboats under power, and whatever the crew says or does is entirely drowned-out by the roar of the engine, even at moderate revs.

I recognise that microphones are sensitive to certain sounds...and this mayn't be an issue for motorboatists...perhaps they like noise...

...but for sailing folk, isn't there a simple way to greatly improve their cruising experiences, which inevitably include periods under power, by constructing serious sound-deadening bulkheads around the Volvo/Yanmar? A vented box, within the box that is the engineroom?

I admit, I ask in total ignorance. But the supplied housings for diesel auxilliaries, don't seem to have kept pace with the sophistication and power and downsizing of the ironmongery itself. Am I wrong? And can effective insulation be neatly retro-fitted to old boats?

 

[Tranona]

You can reduce noise significantly with sound deadening materials, and vibration can be virtually eliminated, particularly with a saildrive by the use of flexible mounts and couplings.

However, unlike a car it is difficult for noise to escape, and hulls act as sounding boards with the engines usually right in the middle of the accommodation. This is worse on a small boat with a small engine. Once you move up in size of both engine and boat the situation improves because there is more mass to absorb and isolate the noise. On a Nauticat 331 the engine is just about inaudible, even inside. Even on my Bavaria you can barely hear the engine running from the cockpit, although inside it is quite noticeable.

Suspect most of the boats you look at are older when engines were less sophisticated and little attention was paid to refinement - just grateful the enginee worked and got you home!

 

[Greenheart]

Thanks for those thoughts. Particularly the size factor. Presumably engine noise on deck is partially from the exhaust?

True, almost all the boats I look at are twenty or more years old. I'm curious, to what extent that means they're cursed by the builder's choice of layout/mountings/materials, or whether a boat that's presently a noisy devil, can be hushed up with a bit of modern science...

...if there really are effective cures to the problem, why aren't more enginerooms equipped to keep the higher-frequency sounds inside? I'd think a well-silenced auxilliary would appeal to yachtsmen in the same way central locking does, to car-buyers...a basic "must-have".

 

[Boreades]

Small boats with old two-cylinder engines will have the worst noise and vibration dynamics, because (a) small boat = less damping mass (b) less cylinders = more vibration (c) old engine = cruder design, less in-build balanced components.

 

[Greenheart]

I noticed that manufacturers like Northern Lights, use hefty enclosures for their relatively quiet, slow-running generators. I realise that the transfer of vibration from auxilliary to the hull through mountings that haven't budged for decades, isn't a problem with a quick-fix...

...but wouldn't the decibel-output reduce very significantly with, for example, a simple, substantial plywood & thick soft foam DIY enclosure, placed over the diesel? (I'm assuming a tubular vent/fan would keep the engine cool and allow air intakes to breath, etc).

Has no-one really thought that was worth trying, for the relative peace on board? Or...doesn't such an arrangement help much?

 

[prv]

Has no-one really thought that was worth trying, for the relative peace on board? Or...doesn't such an arrangement help much?

Sure - engine compartments on most modern boats are fairly well soundproofed with foil-faced foam with a heavy layer in the middle (used to be lead, don't know if it still is). Engine mounts are generally soft, and saildrives don't make contact with the hull. Designs that still use shaft drives can fit an Aquadrive universal joint to decouple the engine from the shaft, though I don't know if anyone fits these as standard.

I think you're just looking at pictures of old boats.

Pete

 

[Greenheart]

I think you're just looking at pictures of old boats.

Guilty.

I wonder how costly it is, and how effective, to retro-fit the measures you describe, aboard an elderly AWB/MAB...

 

[Deleted member 36384]

I noticed that manufacturers like Northern Lights, use hefty enclosures for their relatively quiet, slow-running generators. I realise that the transfer of vibration from auxilliary to the hull through mountings that haven't budged for decades, isn't a problem with a quick-fix...

...but wouldn't the decibel-output reduce very significantly with, for example, a simple, substantial plywood & thick soft foam DIY enclosure, placed over the diesel? (I'm assuming a tubular vent/fan would keep the engine cool and allow air intakes to breath, etc).

Has no-one really thought that was worth trying, for the relative peace on board? Or...doesn't such an arrangement help much?

The Rival 41C (1973) was specified with two engine sizes: Perkins 4236 and the smaller 4108. The smaller engine on the plans is shown mounted inside a sound proofed box, inside the sound proofed engine space. I am not aware if it was ever produced like that. One issue with the box within the box is access. A nice big space, with a small engine is a joy to work on, so perhaps it was never built that way.

You can see the plan here: http://www.rivalowners.org.uk/brochures/brr41.htm Scroll to the right and click on the sectional plan and elevation views, not the isometric sectional views.

 

[Evadne]

Guilty.

I wonder how costly it is, and how effective, to retro-fit the measures you describe, aboard an elderly AWB/MAB...

It can be done. I did that to mine, sort of. I fitted Halyard insulation to all the bulkheads that intrude into the cabin and the noise level easily halved. I can now use the VHF under power, and hear the replies. There is a huge space under the cockpit with water tanks and prop shaft and not much else that it would be tricky to line, although I keep telling myself that I'll get a round tuit one day. It is noisier in the cockpit than in the cabin. (1960's folkboat tpe boat, Yanmar 1GM).
OTOH, a noisy little engine is one of the incentives to sail and not to motor, so it's not all bad.

 

[prv]

I wonder how costly it is, and how effective, to retro-fit the measures you describe, aboard an elderly AWB/MAB...

Sticking up foam should be reasonably straightforward as long as you have the space for it. Engine bays with limited access, like mine, would be best done with the engine out. Decent soundproofing foam is not cheap though, and bits of old mattress don't work as well as you'd want (the heavy layer is necessary to block the full range of frequencies).

Pete

 

[Georgio]

Just looked and there appears to be three different types of sound insulation (from Halyard)...

Maritex
-
An immensely tough fibreglass cloth with a sealed metallised skin so it cannot absorb oil. It won’t tear or fray. It looks heavy duty, and it is fire zero rated. Maritex is simply the best facing in the Halyard range. Maritex is fire zero rated to BS 476 parts 6 and 7.

Sealglass-

A tough off-white glass cloth, sealed against oil. The cloth is extremely tough and will not tear. The sealant will burn off in a fire. The material meets the ISO 9094 fire requirements of the EU Recreational Craft Directive.

Re-inforced silver polyester
-
This facing meets the requirements of the Recreational Craft Directive. It provides a seal to keep oil out. You can pierce it, but it has a re-inforcing layer behind it. It will burn, but once laminated in place it meets the ISO 9094 fire requirements of the EU Recreational Craft Directive. In a fire the facing will burn, but not the foam behind it.

Which is best?

 

[prv]

Just looked and there appears to be three different types of sound insulation (from Halyard)...

Those seem to refer to the outer skin - the silver-foil-like stuff - rather than the actual insulation.

Pete

 

[Georgio]

Those seem to refer to the outer skin - the silver-foil-like stuff - rather than the actual insulation.

Pete

Yes, these are the three options for the outer (or inner, engine facing) layer. Just wondered if there was any guidance on this or does it not really make much difference.

One of the jobs this winter is to replace the 1978 soundproofing that has seen better days and should have been replaced when the engine was done.

 

[prv]

Maritex
-
An immensely tough fibreglass cloth with a sealed metallised skin so it cannot absorb oil. It won’t tear or fray. It looks heavy duty, and it is fire zero rated. Maritex is simply the best facing in the Halyard range. Maritex is fire zero rated to BS 476 parts 6 and 7.

Which is best?

Going out on a limb here, but I'm going to suggest it's the one which has "this is the best in our range" written against it?



To me it looks like they're in order of descending quality (and presumably price to match).

Pete

 

[Greenheart]

The Rival 41C (1973) was specified with two engine sizes: Perkins 4236 and the smaller 4108. The smaller engine on the plans is shown mounted inside a sound proofed box, inside the sound proofed engine space.

I see what you mean about the enclosure. Lovely boats, those bigger Rivals...any idea how many 41' hulls they built?

Accepting that any additional, interior DIY enclosure needs to allow rapid disassembly for work on the engine, I'm still thinking they ought to be more commonplace than they seem to be...

Fishing through Boatshed for engine pics, the first four I found were from 70s/80s boats of popular design...and none look as well-insulated from the rest of the accommodation as would be desirable, or (I suspect) easily possible...

View attachment 20374

...now of course, I'm having trouble finding more than one of the pics to illustrate my point...

 

[Greenheart]

Prout snowgoose...

View attachment 20375

Dammit, why can't I upload more than one pic, per post? Other people seem to manage it. Anyway, loads of pictures there, with (apparently) floor panels removed above, revealing a ruddy great engine, free to deafen everyone in the cockpit/cabin.

I'm sure it needn't be that way.

 

[johnalison]

Our old Sadler 29 came with foam lining in the engine box but was quite noisy. I replaced the lining with proper stuff with a fibreglass surface and a layer of lead, which is necessary to absorb sound. It was certainly a lot better after this messy job but of course diesel vibration remained.

A saildrive gives a much smoother installation and my present HR 34 has acceptable noise levels. The companionway steps tend to vibrate at certain speeds and most of the noise in the cockpit comes from the engine air intakes which are located on the outside of the coamings.

 

[fishermantwo]

My yacht has a "new" Volvo md7b. Its enclosed on 3 side in a box. Its not all that noisy and probably no noisier than the 3 cylinder Kubota auxiliary I had in my fishing boat.

I think if your considering improving the noise limits on your vessel it might pay to investigate how modern diesel cars are sound proofed. There seems to be a trend to identify the source of the noise on the engine and apply a pad directly to that item enclosing it and trapping the noise. With modern materials it is possible to make a series of padded bits to wrap nearly all the engine.

 

[causeway]

Prout snowgoose...

View attachment 20375

Dammit, why can't I upload more than one pic, per post? Other people seem to manage it. Anyway, loads of pictures there, with (apparently) floor panels removed above, revealing a ruddy great engine, free to deafen everyone in the cockpit/cabin.

I'm sure it needn't be that way.

Imgur.com is a good, easy place to upload photos.

 

[snowleopard]

It is fairly common to insulate the bulkheads around an engine. I came across a material that consists of sheet lead enclosed in thin wadding and an oil-proof fabric, a total of 1/2" thick. It's quite effective. Unfortunately you can't generally insulate the bilge so sound from the engine gets transferred into the structure of the boat.

As has been said, 2-cylinder engines are the worst for vibration as, in a 4-stroke engine, the pistons move together not in opposite directions. Anyone who ever rode an old BSA or Triumph twin can attest to that.