Are BMCs always noisy?

[Theo]

Is there anything that I can do to quieten my engine?

 

I have already added the heavy, squashy sound insulation to the engine cover boards and the sides of the compartment so there's little air transmitted noise. The water silencer is really good. The problem is the noise that propagates through the boat's structure. The engine is bolted to wooden bearers with no rubber cushioning. So is it sensible to try to add flexible engine mounts?

 

Nick

[Albion]

Is there anything that I can do to quieten my engine?

 

I have already added the heavy, squashy sound insulation to the engine cover boards and the sides of the compartment so there's little air transmitted noise. The water silencer is really good. The problem is the noise that propagates through the boat's structure. The engine is bolted to wooden bearers with no rubber cushioning. So is it sensible to try to add flexible engine mounts?

 

Nick

They aren't inherently noisy but it will depend on that mounting. Is the engine bolted through the wood AND bearer with the one bolt at each foot or is the engine bolted to the wood and the wood bolted to the bearer in a slightly different place. The first method will transmit the noise to the hull and the second will deaden the transmitted vibration due to the cushioning of the wood.

Having said that I had a Gardner 4LK bolted directly to the bearers (very solidly installed bearers admittedly with flitch plates and other plating) and there was no excessive vibration or noise from such a big lump.

Roger

[David Schweizer]

The BMC 1,5 on our boat is bolted directly onto steel bearers, which are welded to the hull. Whilst it creates a very solid and reliable insallation, it does cause the boat to vibrate noisily underway. The only solution would probably be to install flexible rubber mountings (if there is room!) but they are not without their problems.

[Tony Brooks]

Photos please. The official BMC marinisers originally used the ordinary vehicle front mounts on a steel cross member and funny "top hat" mounts at the back. To the unwary these can look like solid mounts as you describe. The rear mounts can collapse over the years so the heads of the securing screws drop onto the steel engine beds and transmit noise/vibration. So a photo will help identify if your engine is like this.

[pete.i]

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

[p6rob]

Mine has solid engine mounts, vibrates through the boat and is noisy. I'm planning on fitting more sound proofing, rubber engine mounts and an engine steady bar some time in the not too distant future. More pressing things to spend money on at the moment though.

 

Rob

[pete.i]

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

Mine vibrates like hell when I push it too fast which now that I'm on the Air and Calder navigation I have to do occasionally just for the hell of it but more often that not to get out of the way of them big ships and those plastic boats that do 90 miles an hour down that particular cut. My engine mounts are solid on to the bearers. I know this because a) Leo told me they are I had to undo the back mounts when I changed the gearbox.

 

 

HHHMMMMMMMMM how did that smiley, winkey, yellow thingy get in there. Is this forum haunted??

 

 

OH MY GIDDY AUNT IT'S HAUNTED I@M OFF>

Edited April 6, 2015 by pete.i

[Galeomma]

Mine is rubber mounted, doesn't vibrate much and is reasonably quiet.

[alan_fincher]

If Theodora's BMCis particularly noisy, could this perhaps be related to the highly unusual drive arrangements, which, IIRC, involve either belts or chain to transmit power to the shaft that actually lies below the engine.

 

Whilst these engines are seldom ultra-quiet, in my experience they are equally not usually particularly noisy.

[Iain_S]

 

 

HHHMMMMMMMMM how did that smiley, winkey, yellow thingy get in there. Is this forum haunted??

 

 

OH MY GIDDY AUNT IT'S HAUNTED I@M OFF>

 

b ) (without the space)

[pete.i]

And the multitude of repeated instances of my OP????? I didn't do that. The forum is haunted I tell you.

[luctor et emergo]

All BMCs are noisy.. proper engines are a joy to listen to....

 

 

;-)

[Mike Jordan]

There is a cheap and effective method of reducing the noise in an article in the July 2014 edition of Waterways World.

You can look at it in the back issues and download it for a small sum.

There is no better cure for vibration than and adequate weight of flywheel, flexible mounts, and a flexible drive

shaft. That means a thrust bearing and two flexible couplings not just one.

Most inland boat builders still go for the cheapest method of rigid mountings and rigid shaft, any competent boater

can do a better job for limited cost, every penny will be worth it when you are boating in near silence. My objective is to be able to hear the water emerging from beneath the counter over the sound of the engine. Above all, don't let anyone sell you a hospital silencer!

[RLWP]

Photos please. The official BMC marinisers originally used the ordinary vehicle front mounts on a steel cross member and funny "top hat" mounts at the back. To the unwary these can look like solid mounts as you describe. The rear mounts can collapse over the years so the heads of the securing screws drop onto the steel engine beds and transmit noise/vibration. So a photo will help identify if your engine is like this.

 

I have one in like that at the moment. I'll take some photos

 

Richard

[pete.i]

There is a cheap and effective method of reducing the noise in an article in the July 2014 edition of Waterways World.

You can look at it in the back issues and download it for a small sum.

There is no better cure for vibration than and adequate weight of flywheel, flexible mounts, and a flexible drive

shaft. That means a thrust bearing and two flexible couplings not just one.

Most inland boat builders still go for the cheapest method of rigid mountings and rigid shaft, any competent boater

can do a better job for limited cost, every penny will be worth it when you are boating in near silence. My objective is to be able to hear the water emerging from beneath the counter over the sound of the engine. Above all, don't let anyone sell you a hospital silencer!

Well okay. Whilst I don't entirely disagree with you that is an extermely expensive and labour intensive way to quieten a boat that is already built. I haven't read that article although I will. The bit about hospital sileners needs explanation. Not a lot of point in coming on and saying stuff like that and then leaving it up in teh air as you did. The Op (as do I ) ways to quieten his engine down and as I have a hospital silencer on mine and he, probably, has as well, telling us why it would be a bad idea to buy a hospital silencer would be an awfully good idea on your part.

[David Schweizer]

There is a cheap and effective method of reducing the noise in an article in the July 2014 edition of Waterways World.

You can look at it in the back issues and download it for a small sum.

There is no better cure for vibration than and adequate weight of flywheel, flexible mounts, and a flexible drive

shaft. That means a thrust bearing and two flexible couplings not just one.

Most inland boat builders still go for the cheapest method of rigid mountings and rigid shaft, any competent boater

can do a better job for limited cost, every penny will be worth it when you are boating in near silence. My objective is to be able to hear the water emerging from beneath the counter over the sound of the engine. Above all, don't let anyone sell you a hospital silencer!

 

Interestingly every qualified marine engineer who has put his head down the engine hole in our boat has said "oh good, solid mounted" or something to that effect, adding that it is the most reliable system, the only maintenance requirement being to check the security of the mountings every once in a while. Of course lining up a solid mounted engine requires a fair degree of skill and competence, if bearings are not going to be compromised, something which (apparently) is less important with flexible mounts and multiple flexible couplings.

 

Personally I have no intererest in making the boat silent, it is a diesel, diesels are noisy. The BMC inside it's sound insulated box is no where nearly as noisy as a slow revving engine in an open steep engine room. I am quite happy to live with it.

[Mike Jordan]

A hospital silencer is both expensive and usually large in size, its sole purpose is to reduce the noise coming from

the exhaust pipe. The lions share of the noise from the engine comes from the surfaces of the engine itself, the

diesel clatter is much louder than the exhaust note. Having spent money on the problem, its not uncommon for the

boater to claim a great improvement when all that's been achieved is a reduction in exhaust noise rather than any

real improvement in the diesel rattle and clatter.

[pete.i]

A hospital silencer is both expensive and usually large in size, its sole purpose is to reduce the noise coming from

the exhaust pipe. The lions share of the noise from the engine comes from the surfaces of the engine itself, the

diesel clatter is much louder than the exhaust note. Having spent money on the problem, its not uncommon for the

boater to claim a great improvement when all that's been achieved is a reduction in exhaust noise rather than any

real improvement in the diesel rattle and clatter.

Okay thanks for that. I can see where you are coming from. My BMC does make a lot more noise than my exhaust and the vast majority of the noise is diesel clatter, mechanical clatter and vibration noise.

[Iain_S]

And the multitude of repeated instances of my OP????? I didn't do that. The forum is haunted I tell you.

 

Probably vibration from the BMC

 

Iain

[Theo]

Well okay. Whilst I don't entirely disagree with you that is an extermely expensive and labour intensive way to quieten a boat that is already built. I haven't read that article although I will. The bit about hospital sileners needs explanation. Not a lot of point in coming on and saying stuff like that and then leaving it up in teh air as you did. The Op (as do I ) ways to quieten his engine down and as I have a hospital silencer on mine and he, probably, has as well, telling us why it would be a bad idea to buy a hospital silencer would be an awfully good idea on your part.

No hospital silencer. I have a water cooled exhaust and a big plastic box type thing under the engine through which the exhaust goes. This arrangement gives very low exhaust nouise levels.

 

N

Edited April 7, 2015 by Theo

[Theo]

If Theodora's BMCis particularly noisy, could this perhaps be related to the highly unusual drive arrangements, which, IIRC, involve either belts or chain to transmit power to the shaft that actually lies below the engine.

 

Whilst these engines are seldom ultra-quiet, in my experience they are equally not usually particularly noisy.

I suppose that might be a possibility, Alan. It is a belt drive and I suppose that the belts will contribute little to the noise but the output shaft from teh gearbox is ver short and although it has a slightly flexible coupling it might transmit some vibration to the structure.

 

N

[Alistair Anderson]

 

Interestingly every qualified marine engineer who has put his head down the engine hole in our boat has said "oh good, solid mounted" or something to that effect, adding that it is the most reliable system, the only maintenance requirement being to check the security of the mountings every once in a while. Of course lining up a solid mounted engine requires a fair degree of skill and competence, if bearings are not going to be compromised, something which (apparently) is less important with flexible mounts and multiple flexible couplings.

 

Personally I have no intererest in making the boat silent, it is a diesel, diesels are noisy. The BMC inside it's sound insulated box is no where nearly as noisy as a slow revving engine in an open steep engine room. I am quite happy to live with it.

Engine noise and exhaust fumes are a couple of serious drawbacks to boating for me. Diesel cars are much more refined than they used to be and it is hardly surprising that most people want to minimise noise on their boats.. I remember describing an early boating holiday on a hire boat with an SR2 as 'like a holiday on a dump truck'.

 

Flexible engine mountings can cushion the impact of severe propellor fouling such as something jammed between the prop and the skeg.

[David Schweizer]

Engine noise and exhaust fumes are a couple of serious drawbacks to boating for me. Diesel cars are much more refined than they used to be and it is hardly surprising that most people want to minimise noise on their boats.. I remember describing an early boating holiday on a hire boat with an SR2 as 'like a holiday on a dump truck'.

 

Flexible engine mountings can cushion the impact of severe propellor fouling such as something jammed between the prop and the skeg.

 

I am not sure that "most people" actually think about it very much. Rather, I suspect, many just accept it, and some are positively enthusiastic about the sound that their slow revving engine makes.

 

Your early boating experiences are hardly surprising, scrapped diesel dumpers were a regular source of engines for recreational craft in the 1960's.

[Alistair Anderson]

 

I am not sure that "most people" actually think about it very much. Rather, I suspect, many just accept it, and some are positively enthusiastic about the sound that their slow revving engine makes.

 

Your early boating experiences are hardly surprising, scrapped diesel dumpers were a regular source of engines for recreational craft in the 1960's.

I appreciate that there are many enthusiasts who like old engines but for many years hire companies used to market their boats as having 'quiet water-cooled engines'.