Engine bearers, oak or steel?

[casper ghost]

I've always fitted oak bearers to engines in boats, bolted to the engine then bolted seperately to the steel.

A chap I spoke to, who fits Gardner engines and has done loads over the last 20 years, says I should not use oak and just bolt the engine direct onto steel bearers as that's what he does. He even says that he has had to remove oak bearers from some boats and fit steel bearers as he says this is the best way..

 

Any one else know? We've just fitted an HR2 and have used oak, also my Sabb and my dad's SL2..

 

The engine i'm shortly going to fit is a Ruston 2VTH.

[Arnot]

I've always fitted oak bearers to engines in boats, bolted to the engine then bolted seperately to the steel.

A chap I spoke to, who fits Gardner engines and has done loads over the last 20 years, says I should not use oak and just bolt the engine direct onto steel bearers as that's what he does. He even says that he has had to remove oak bearers from some boats and fit steel bearers as he says this is the best way..

 

Any one else know? We've just fitted an HR2 and have used oak, also my Sabb and my dad's SL2..

 

The engine i'm shortly going to fit is a Ruston 2VTH.

I am using Tico Pad with engine bearers designed for the purpose. If you want I can e-mail the design of the bearers.

 

Regards

 

Arnot

[RLWP]

I am using Tico Pad with engine bearers designed for the purpose. If you want I can e-mail the design of the bearers.

 

Regards

 

Arnot

 

Could you let us know more on your plans to use Tico pads please? Would this system work with a BMC 1.8 and be quieter than the standard flexible mounts?

 

Richard

[Athy]

When Mel Davis fitted our Gardner he specified solid oak bearers as he reckoned that they reduced vibration. As the engine does not vibrate much I guess they work.

[NB Esk]

Oak.

 

 

Pic shows 4"x 4" english oak. You can see my method of bolting. The ones from the bedframe go all the way thro', while the ones to the engine mounts stop short.

 

Hope this helps...

[Arnot]

Could you let us know more on your plans to use Tico pads please? Would this system work with a BMC 1.8 and be quieter than the standard flexible mounts?

 

Richard

If someone can successfully expain to me how to include a PDF or an image in a posting, I will post the plans.

 

Would it be quieter than the standard flexible mounts with a BMC 1.8? If the standard mounts are in good condition, frankly I doubt it. In my experience the majority of the noise from these is airborne not structurally transmitted so no amount of fiddling with the mountings will help. I would have thought that lashings of acoutic foam round the engine hole would help a lot but I can't help thinking that a silk purse in not on the menu here. Sorry!

 

Regards

 

Arnot

[RLWP]

If someone can successfully expain to me how to include a PDF or an image in a posting, I will post the plans.

 

Would it be quieter than the standard flexible mounts with a BMC 1.8? If the standard mounts are in good condition, frankly I doubt it. In my experience the majority of the noise from these is airborne not structurally transmitted so no amount of fiddling with the mountings will help. I would have thought that lashings of acoutic foam round the engine hole would help a lot but I can't help thinking that a silk purse in not on the menu here. Sorry!

 

Regards

 

Arnot

 

It's not noise but vibration I would like to reduce. Particularly the frequency that rattles glasses into the kitchen sink.

 

Richard

[nb Innisfree]

IMO for an engine to be bolted down solid it req the engine to be massively built to absorb vibrations, wouldn't think a BMC comes in to this category. In his book Graham Booth had his engine (an old Lister twin IIRC) bolted straight on to the mountings, steel to steel, with no ill effects. I think if mountings are massive and solid enough then this would be ok

[Arnot]

It's not noise but vibration I would like to reduce. Particularly the frequency that rattles glasses into the kitchen sink.

 

Richard

How sure are you that the existing flexible mountings have not collapsed?

 

Regards

 

Arnot

[paulcatchpole]

IMO for an engine to be bolted down solid it req the engine to be massively built to absorb vibrations, wouldn't think a BMC comes in to this category. In his book Graham Booth had his engine (an old Lister twin IIRC) bolted straight on to the mountings, steel to steel, with no ill effects. I think if mountings are massive and solid enough then this would be ok

 

Both our ST2 and SR3 are bolted solidly to the steel engine beds.

 

The ST2 is bolted to a structure that doesn't look very over-engineered and the vibrations can be felt through the whole boat, although it's not exactly a problem as such.

 

The SR3 we've not had running yet, so no idea what it'll do, but the engine bearers (and the rest of the hull) look massive in comparison to the other boat.

 

PC

[Albion]

IMO for an engine to be bolted down solid it req the engine to be massively built to absorb vibrations, wouldn't think a BMC comes in to this category. In his book Graham Booth had his engine (an old Lister twin IIRC) bolted straight on to the mountings, steel to steel, with no ill effects. I think if mountings are massive and solid enough then this would be ok

 

My Gardner 4LK was bolted straight to steel bearers that were then welded into the boat with substantial reinforcing plates etc. There was a technical reason that this method was chosen that relates to providing a drive to a 240V alternator driven by the engine. I never had a problem with vibration from this big lump of engine but it was very well built into the shell. IMO if the bearers and reinforcing are substantial enough and well tied in to the boat there shouldn't be much of a problem.

Roger

[alan_fincher]

It's not noise but vibration I would like to reduce. Particularly the frequency that rattles glasses into the kitchen sink.

 

Richard

When you find the answer, please be sure to spread the "secret".

 

Simple work around though is to put things into the lowest point, (i.e. sink bowl) before starting up, and gravity is less likely to do it's worse.

 

I'm not a mechanical engineer, but have always though the typical mounting arrangements on something like a BMC to be "odd".

 

Frankly putting in solid engine bearers, then expecting the engine and gearbox to "float" several inches above on what are effectively 4 lengths of screwed rod, with nuts above and below hardly seems the best, particularly as vertical "rods" aren't really designed to deal with backwards and forwards thrust.

 

That said, I have a suspicion that if I go unwrapping bandages that our BMC is "hard wired" to the hull through it's exhaust pipe. There is nothing under the "swaddling cloth" that looks much like a flexible section. It's not impossible that much vibration comes via our exhaust pipe, but I've not disturbed things enough to really know what goes on there.

 

Our most irritaing vibrations are....

 

1) Morco cover - the old D51B used to be bad enough but it's D61B replacement could hardly vibrate more.

2) "Drop back" lights in the top of our windows, that just lie there as largely unsupported sheets of glass. Each seems to be set off at subtly different engine revs, despite being dimensionally identical.

[NB Alnwick]

It's not noise but vibration I would like to reduce. Particularly the frequency that rattles glasses into the kitchen sink.

 

Richard

 

This is easily achieved - remove the diesel engine and get yourself a horse. I believe they are vibration free.

 

On the other hand, you could try a steam turbine or a triple expansion engine based on Willan's patent

[carlt]

When you find the answer, please be sure to spread the "secret".

 

Vintage engine on wooden bearers bolted down to a wooden boat.

[NB Alnwick]

Our Kelvin K3 is bolted directly onto steel girders that are welded to the base plate and engine room bulkheads. The engine does not vibrate at all - but at certain speeds, the rest of the boat does . . .

 

Vintage engine on wooden bearers bolted down to a wooden boat.

 

Quite right - diesel engine in a wooden boat sounds and feels completely different.

 

I always knew that wood had some advantages

[RLWP]

How sure are you that the existing flexible mountings have not collapsed?

 

Regards

 

Arnot

 

This is a fair point. Although with a whole new set of mountings the vibration in the boat is far from good.

 

With the gearbox and half the aquadrive hanging off the back and half the engine weight as well, the rear mountings do have an awful lot of load on them.

 

We have four of the R&D mounts like these:

 

The engine is a BMC 1.8 with a PRM gearbox and an aquadrive. What do other people have?

 

Richard

Edited September 18, 2009 by RLWP

[alan_fincher]

This is a fair point. Although with a whole new set of mountings the vibration in the boat is far from good.

 

With the gearbox and half the aquadrive hanging off the back and half the engine weight as well, the rear mountings do have an awful lot of load on them.

 

We have four of the R&D mounts like these:

 

The engine is a BMC 1.8 with a PRM gearbox and an aquadrive. What do other people have?

 

Richard

Richard,

 

We have exactly those mounts, with a BMC 1.8 and Newage PRM Delta box.

 

The only difference I can see is that we have a simple R&D flexible coupling in the drive, (i.e. no AquaDrive, so our porop thrust is taken on the engine, and ultimately on those mounts.

 

Although there are many variants of such mounts, nearly all share the same "thread sticking up with adjuster nuts on" design.

 

It lever "feels" right to me to mount well over half a tone of vibrating mass in this way. I'm not really surprised in our case that after mabe 14 years various fixings have decided they have had enough.

 

On some of our mounts those "oil shields" will not stay attached, undoubtedly meaning oil gets into the "flexible" bit.

 

I don't know how you can tell for certain if one of these mounts needs replacing, (assuming it's still all in one solid piece) - does anybody have any advice on that, please ?

 

Here's one of ours, although I was unaware of that extra loose nut on it until I saw the picture!

 

Edited September 18, 2009 by alan_fincher

[Arnot]

This is a fair point. Although with a whole new set of mountings the vibration in the boat is far from good.

 

With the gearbox and half the aquadrive hanging off the back and half the engine weight as well, the rear mountings do have an awful lot of load on them.

 

We have four of the R&D mounts like these:

 

The engine is a BMC 1.8 with a PRM gearbox and an aquadrive. What do other people have?

 

Richard

Like Alan, I have always been a bit suspicious of this type of mounting for diesel engines that have to transmit the rotational thrust to the hull. Whilst they do isolate the engine from the hull they are relatively undamped and tend to allow the thing to leap about a bit under certian conditions. I think that another factor is that the rotational force is not regular and has a cyclical nature related to the propeller and gearbox ratio, if the frequency of this is similar to the fundamental resonance of the mounting/mass of the engine (or an odd harmonic) this can be quite alarming and lead to premature mounting failure.

 

I also have some reservations about the "Aquadrive" and "Python" drive systems. It seems to me that they rely on metal to metal contact to transmit the torque and thus bypass the vibration isolation that the mountings attempt to achieve.

 

Question; is the level of vibration related to the engine speed or load?

 

As I see it, the benefit if the tico pad system is that the vibration is isolated from the hull but the high damping factor prevents oscillation of the engine mass. Of course this will only be fully effective if the drive is also isolated with somthing like a tyreflex coupling. Essentially there should be no metal to metal contact between the engine and the hull. I think that the worst case could be the combination of traditional mounts like you have and a rubber coupling on the drive shaft...

 

Can anyone tell me how to post a pdf - please?

 

Regards

 

Arnot

 

Regards

 

Arnot

[RLWP]

<snip>

 

Question; is the level of vibration related to the engine speed or load?

 

<snip>

 

Can anyone tell me how to post a pdf - please?

 

Regards

 

Arnot

 

Regards

 

Arnot

 

The worst vibration is at idling speed, either in or out of gear.

 

The pdf. You would have to upload it to somewhere and then link to it from here.

 

Richard

[NB Alnwick]

>snipped<

 

Here's one of ours, although I was unaware of that extra loose nut on it until I saw the picture!

 

 

Obviously it is important to adjust the height and inclination precisely - that loose nut may be an indication that the engine has moved out of alignment and this could cause excessive vibration and wear to the propshaft bearing(s) - could this be linked to your broken bolt incident?

[Arnot]

The worst vibration is at idling speed, either in or out of gear.

On that basis I suspect that the problem is combination of truly awful dynamic balance in the engine and lack of damping on the engine mounts. In the automotive sector a popular and reaonably effective fix is to attach a gas strut that amounts to a shock absorber between the top of the engine and the chassis (or hull in the case of a boat). This then prevents the rotational engine oscillation at certain speeds. I dont know of anyone who has tried it in a boat though.

 

The pdf. You would have to upload it to somewhere and then link to it from here.

Thanks, I will try it out...

 

Regards

 

Arnot

[RLWP]

Thanks, I will try it out...

 

Regards

 

Arnot

 

Like this: RandDMarine pdf

 

Richard

 

There are several different kinds of mount in that pdf. I'll set to and do the sums to see what works out.

[FadeToScarlet]

 

Cor, I wish my engine was that clean! I think I'll just try and get the boatyard to pressure wash it when they're working on it...

 

I once spent 6 hours cleaning it and the bilges.

 

Then, the same afternoon, developed an oil leak. Grrr!

 

Back on topic, I suppose that you're not only taking forwards and backwards thrust on the vertical rods, but those rods are bedded in flexible rubber- so would allow even more bending.

 

I'm getting lots of ideas about how I want to alter my engine mounts, and what bits to specify the boatyard fit when they're working on it. I've learnt that a flexible section in the exhaust pipe is probably a good idea!

[Guest z1100r]

I agree with everything some have said here....I dont like these mounts.

I've just replaced the ones Alan has because one front one had worn out. The plastic cover had felll off and the centre stud was clanging away on the bearer....The rubber had fallen to bits. Some may have read my 'prop to gearbox' thread in which thrust is mentioned...my drive system means that prop thrust is passed to engine mounts....well these engine mounts have to be the worst design posible for taking thrust. Narrowboats engine/drive systems dont seem to have been thought out properly in the 70's and 80's and early 90's. Theres so many boats in existance with awful engine gearbox installations.

 

I've decided to change mine .....its having largeish soft aquadrive engine mounts (for nice engine vibe reduction)...retaining the current self aligning bearing (for stern tube protection) and the current vetus rubber coupling (for slight engine/gearbox mis-alignment and isolation of engine)...but having an additional tie bar to hold engine/box against thrust.

 

That should be engine isolated...propshaft true...and thrust forward/backward movement taken care of.

 

The motor is as sweet as a nut...in fact each component part is quite good...its just the ill thoughtout way its all been put together thats the problem.

[Arnot]

Like this: RandDMarine pdf

 

Richard

 

There are several different kinds of mount in that pdf. I'll set to and do the sums to see what works out.

Thanks but ideally what I wanted to achieve was to embed the pdf in a post so that it displayed as a part of it rather than as a link. I always find that having to flip back and forth to links interrupts the communication process.

 

The dampers on the pdf you linked to are, as far as I can see, typical of the problem - no damping! Have a search on e-bay or gogle for engine damper and there are a few examples of the sort of thing and even some fairly cheap gas strut dampers.

 

Regards

 

Arnot