Hard vs Soft Engine Mounts

[charliehows]

Originally Posted by stillbuilding

This discussion has me thinking I will revert to hard mounting my Perkins and avoid the costs of soft mounting and flexible drive train. Steel boat but I think 6 cylinders may not be too bad.

Anyone with hard mounts care to comment on 6 cyl or Perkins specifically.

cant comment on perkins per se, but if you are designing, one thing i think might be worth mentioning is the distance between g.box mount and fwd stern gland - on my boat more than a metre, and the stern tube is pretty long too - i'm just suggesting it might be worth thinking about or discussing with someone with experience in hard mounted engine systems. I would say in relation to a 6 cyl engine - properly tuned it has to be a lot smoother than a 30 year old 2 cyl., but even my old 2 cyl only produces negligible vibrations - and that in a fibreglass hull too.

[ccgarnaal]

Originally Posted by Jim Cate

I am curious how you measured your alignment to that degree of accuracy... .001 mm is one micron, and that is a pretty thin feeler gage!

Cheers,

Jim

I borrowed a laser alignment tool for aligning ships engines from work.
Typo I meant 0.01mm the laser can go slightly more accurate but it gets difficult.

[Icarus]

Originally Posted by GILow

Hello Cruisers,

I have recently purchased a Swanson 42 with a Nissan ED33 diesel, 96HP (marinised by Diecon). The engine has been inspected and found to be in excellent condition and only has 2000 hours. The boat was setup by somebody who really knew what he was doing, but something they have done has me a bit confused.

The engine is HARD mounted to the boat. There are absolutely NO flexible mountings anywhere on the drive train. Needless to say, a 96HP 4 cylinder diesel produces a staggering amount of vibration, even in an 18 ton boat. The gearbox is a BorgWarner Velvet drive (can't remember the model), it too is hard mounted.

I am not about to rush and change anything here, since it is all working very well, but for future planning I would consider soft mounting the engine unless there is a good reason not to. Yes, I do know it will involve a lot of work, but I have tackled and completed much bigger engine jobs than this.

But WHY did he do it that way? I am really reluctant to change anything by this guy, everything has been so well thought out (but OMG, the vibration!), so there must be a good reason. Does anyone know why he might have done it this way?

Matt

Basically there is nothing wrong with a solid set up, it saves buying expensive flexible engine mounts and something like an AQUADRIVE, which is a constant velocity drive designed to take up misalignment and the wobble of the engine and the propeller thrust, more real expense there

A flexible set up requires a thrust bearing on the prop shaft and a flexible connection between shaft ( mounted solid) and the gearbox/engine which when mounted on flexible mounts.
In my opinion the answer to your question is substantial cost saving and eas of installation.

[Wotname]

Love these necrothreads!

Matt, I presume your new Beta is soft mounted- if so, is there a significant improvement with the vibration level?

[GILow]

Originally Posted by Icarus

Basically there is nothing wrong with a solid set up, it saves buying expensive flexible engine mounts and something like an AQUADRIVE, which is a constant velocity drive designed to take up misalignment and the wobble of the engine and the propeller thrust, more real expense there



A flexible set up requires a thrust bearing on the prop shaft and a flexible connection between shaft ( mounted solid) and the gearbox/engine which when mounted on flexible mounts.

In my opinion the answer to your question is substantial cost saving and eas of installation.

No, the flexible setup doesn’t need a thrust bearing, the engine and gearbox provides that bit regardless.

Likewise, no expensive coupling either, the same polyflex coupling is used by both.

The engine mounts are not all that expensive, so really, in this boat, I think it came down mainly to robustness.

Either way, it was horrible and I was glad to see the end of it.

[GILow]

Originally Posted by Wotname

Love these necrothreads!

Matt, I presume your new Beta is soft mounted- if so, is there a significant improvement with the vibration level?

I ended up soft mounting the Nissan. It wasn’t much hassle and did reduce the noise and vibration enormously. I always had problems with the massive cast iron exhaust riser though, just too heavy and it put a lot of strain on the connection to the manifold which would subsequently leak.

The Beta is, of course, soft mounted and a lot smoother and quieter, but then it’s a 2.2 litre four cylinder, not a 3.3 litre four cylinder.

[Icarus]

Originally Posted by GILow

No, the flexible setup doesn’t need a thrust bearing, the engine and gearbox provides that bit regardless.

Likewise, no expensive coupling either, the same polyflex coupling is used by both.

The engine mounts are not all that expensive, so really, in this boat, I think it came down mainly to robustness.

Either way, it was horrible and I was glad to see the end of it.

We installed over a hundred engines in various vessels over the last ten years or so, and had excellent results utilising a flexible CV drive.
Obviously most DIY have a lot more mechanical experience then a professional.
You get this in forums.
Not sure what you referring to...it was horrible?
I think we leave it at that.

[GILow]

Originally Posted by Icarus

We installed over a hundred engines in various vessels over the last ten years or so, and had excellent results utilising a flexible CV drive.

Obviously most DIY have a lot more mechanical experience then a professional.

You get this in forums.

Not sure what you referring to...it was horrible?

I think we leave it at that.

Gosh, good to hear you’ve done so many installs.

But no, I did not need a CV drive, and interesting to note Beta marine didn’t recommend one for the new engine either. They recommended the same polyflex coupling I had with the previous engine. A simple and very robust system. I trust Beta marine to make a good recommendation.

What was horrible was the old hard mounted system, and I was glad to see the end of it. As I noted, it was a pretty simple task to convert, and not all that expensive. I already had the polyflex coupling, the engine mounts from Vetus were, I think, less than AU$500 for the set, and the rest of it was just some simple welding. I made the new engine mounts out of some 12 mm steel plate, tack welded the bits together then had a local welding shop with a proper three phase welder zap them together. That bit cost me $20 and it took them five minutes.

There does seem to be a lot of ways of mounting engines, but I like my simple setup. Things like CV joints just seem expensive and complicated to me, at least at my sorts of horsepower.