Engine noise

[jecuk]

So after bringing Lady Gay up the Thames, I now have a better feel for the engine noise. She is very noisy down below even at 5knots cruising. Also, in he wheelhouse above the engines, at 5kts thames-speed it is also very noisy. To be honest, this is true even at low revs in locks.

I am looking into more soundproofing of the engine bay but am skeptical of how much difference that will make. Do modern diesel engines have appreciably less noise?

 

[ytd]

yes, modern engines make less noise and you seem to get less transmission noise and vibration with a saildrive.
yes, soundproofing works The noisiest boat I ever sailed on was a wooden folkboat with a 20hp Bukh. It just had a ply engine box. It was unbearable below and you had to shout to be heard on deck. After boxing in the transmission, shaft and exhaust pipe and lining everything with 30mm sound absorbing rubber & aluminium material, it was almost quiet. Holes for controls etc should be at the rear of the engine box to minimise engine noise in the cabin.

 

[Lakesailor]

I can never understand why boatbuilders don't use engine mounts and rubber donuts in the shaft assembly.

 

[roly_voya]

engine mounts and shaft couplings are also part of the noise reduction, particularly for structurally transmitted noise. Just gone from a Volvo MD2B to a bigger Beta, more power, drematically less noise and uses less fuel as well. Allow a good budget for instalation, I spent about 25% of the engine cost to do it right including wiring etc for new high power alternator

 

[mortehoe]

The best cheap sound insulator is .....

plasticised vinyl ie off the shelf tiles from B&Q, HomeBase, Focus, Wickes or wherever. Plasticised vinyl is not as good as lead but it works. ie it's only 89% effective.

A common misnomer with sound is the difference between sound absortion and sound insulation. Sound absorbtion in something like closed cell foam will only give a maximum of -3dB. Sound insulation materials are heavy, dense and non-vibratory, hence lead and errrrgh ... plasticised vinyl. Another nasty with sound is that the smallest crack/hole will defeat any sound insulation project ie there MUST be NO Holes whatsoever. This causes problems with air intakes into sound insulated engine spaces: Solution: bring the air in via plasticised vinyl pipe with an internal sound box akin to a car exhaust with extra insulation where it passes beyond the engine compartment to the fresh air.

Note that heat insulation products are incompatible with sound insulation products so the reality is that you should buy and install proper tested sound insulation products with datasheets so that you can calculate the dB reduction .... unless you want to experiment with foamed vinyl and solid vinyl tiles (I have a Bruel & Kjaer sound meter (octave analysis) which I use for my everyday work ... so I can play with vinyl and other materials)

My 1GM10 housing has an effective reduction from 98 to 48dB(A) (8mm total of vinyl type tiles on 12m plywood) which means that you can just hear it against the background daytime motoring/sailing noise. At night in quiet esturaries it sounds loud, but you can still listen to and talk on the mobile phone/VHF. (Cost: on a CO26 £22.00 in 1998 ... probably ~£35 today) Downside: don't buy self adhesive vinyl tiles; they will fall off with 2 years. Use a two part epoxy adhesive such as Treadmaster No15. Use 4 to 6 layers of 3mm tiles with a foam tile layer as layer 2 next the engine side.

The main problems that can't be overcome by simple insulation are the flanking sound transmissions that are induced and reinforced by engine-mounts and propshaft bearings transmission to the hull. These vibrations account for upto ~22% of engine noise heard all around the rest of the boat unless there is a CV propshaft isolator then the flanking transmission can reduce to ~zero.

Effective sound insulation is difficult to achieve. There's a lot of nonsense spouted about it. IMO, if you are unfamiliar with the number crunching that will be necessary for any engine enclosure, then go with a proprietary brand (at a cost well beyond the actual materials cost) and follow their instructions precisely.

Good luck and /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[vyv_cox]

Mortehoe's advice is excellent and clearly based upon practical experience, always the best.

Mine is a lot less technical but I'll write it anyway. My boat came with a Bukh 20 engine and some thin flexible foam around the engine compartment. This looked like the sort of stuff you can buy for furniture recovery, definitely not purpose built soundproofing. I replaced it on the panels all around the engine, top and sides, with Halyard's sheet material, making sure all joints were tight and sealing them with Sikaflex. The rear cover of the engine is GRP, that was covered also. Aft of that the prop tunnel is covered plywood, on top of which are bunk cushions.

This transformed the sound levels, so that we sometimes had to check the exhaust to find whether the engine was running. Some time later we changed the engine to a Yanmar 3-cylinder, which has much softer mountings than a Bukh, and in general the sound levels decreased a little, as might be expected. The engine itself is equally noisy but the transmitted sound has decreased.

A simple test of the effectiveness of the sound proofing is to lift the engine cover when under way. The difference is astonishing.

 

[Gordonmc]

Owning an old woody with the engine bay opening to the bilges, I can't create an enclosed box so am investing in an acoustic blanket to cover the top of the block where most of the valve racket comes from.
Check out http://www.noisekiller.co.uk/materials_more.php#blanket
I might give mortehoe's plasticised vinyl idea a go in conjunction.

 

[mortehoe]

Here\'s the way to go ...

What Vyv did was reality. It's sealing the holes that really counts after you've done the essential acoustitic sealing ./../ and vinyl tiles are heaps cheaper than Halyards Acoustic lining ... If you don't believe me, try it out for yourself : ) /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[PeterGibbs]

Re: Here\'s the way to go ...

Whichever way you go, do not be lured into using egg crate foam. As stated above it has virtually no effect - Westerly used to use it a lot, cheapskates.

Proper accoustic panelling costs £80 for 4 large sheets, last time I looked. It has silver fire resistant fronting, and a sound deadening heavy panel sandwiched between foam sheets. This is the stuff to go for. It's heavy so don't just rely on glueing it into place - screws with washers on the face, if you please.

Some posts here emphasise the need to completely surround the engine - this is desirable but mostly impracticable. I have a top and sides approach to my 50 HP engine and am happy with the noise level. Vibrations reflected downwards have to look after themselves. Don't let a counsel of perfection prevent you from having a go at betterment!

PWG

 

[jecuk]

Re: Here\'s the way to go ...

So I need foil fronted acoustic sandwich? There seem to be so many variations.....

Thanks for all the advice.

 

[mortehoe]

Seriously, Acoustics is VERY complex

Although sound energy is trivial in terms of wattage, it's the devil to destroy. If you seriously want to insulate for sound then you have to have an indepth knowledge of octave calculations and the physics of materials at quantum levels.

The simplest solution to sound insulation is 'line the source with the appropriate thickness of sheet lead; ensure that all panels capable of vibrating are asymetric; have neither joints nor holes and insulate the air intake/engine heat ventilation to the same degree and the lining.'

You will still be affected by engine vibration through the soft mounts making the hull resonate at certain frequencies. Ditto the propshaft unless you have a CV (vibration) disconnection ....

Take the plunge and go for the densest and thickest lead/foam sandwich that you can affort. Stick it on with epoxy. Just ensure that you tape up ALL gaps and holes because even the smallest acoustic hole/gap will obviate all of your good sound reducing works.

IMO, PBO should write an article on (series of articles on) comfort on boats which should include "How to make your engine silent."