Hard vs Soft Engine Mounts

[shakey doug]

G' day,
I use have used polyflex mounts & couplings with great success for many years. I suggest you make contact via their website polyflex.com.au/ they have all the answers & recommendations.

[captain58sailin]

I had an increase in vibration once and thought that one of the motor mounts had failed, upon further investigation found that one of the mounts had loosened and the oil pan was sitting on the bottom of the boat and transmitting the vibration. I did contact Polyflex about new mounts when I thought mine were shot and they were very helpful and responsive.

[GILow]

Thanks for the recommendation, if I decide to soft mount the engine I will look them up. Calculating the stiffness for the engine mounts is a bit of a complex equation, these sorts of people may be able to help.

Strangely, I can not imagine these guys giving me a convincing case to stay with the hard mounts, given what the sell, so I am still wondering WHY he hard mounted the engine, I feel there has to a good reason.

[Cherp]

I think the hard-mounting thing comes from practice in earlier times. Fishing boats, generally wooden and heavy, often used Gardner engines which were big, heavy and very slow revving. The fishermen hard- mounted them to big heavy beds and it worked fine. They were not too fussed about noise transfer. Then along came the more ,modern high-revving engines and lighter hulls for pleasure boats. Some people just stayed with the old ways as times changed.

[GILow]

Originally Posted by Cherp

I think the hard-mounting thing comes from practice in earlier times. Fishing boats, generally wooden and heavy, often used Gardner engines which were big, heavy and very slow revving. The fishermen hard- mounted them to big heavy beds and it worked fine. They were not too fussed about noise transfer. Then along came the more ,modern high-revving engines and lighter hulls for pleasure boats. Some people just stayed with the old ways as times changed.

He he... I think of the Nissan ED 33 as big, heavy and slow revving, but everything is relative! You have a good point and it may be that simple.

The absence of anyone knowing a really compelling reason to stay with the hard mounts it giving me hope, I think it may be safe to convert it to soft mounts when I get the time by the sound of things. Hopefully it is just a case of old fashioned belts and braces thinking and I really would like to see if I can smooth it out a little.

Matt

[delmarrey]

Originally Posted by GILow

The absence of anyone knowing a really compelling reason to stay with the hard mounts it giving me hope, I think it may be safe to convert it to soft mounts when I get the time by the sound of things. Hopefully it is just a case of old fashioned belts and braces thinking and I really would like to see if I can smooth it out a little.

Matt

Maybe to save $$$$$$$$ and labor.

[GILow]

Oh you hardened cynic! When have you EVER known a boatie to try and save labour or money...?

[stillbuilding]

Many engines are well balanced and contribute little vibration if hard mounted. Once well set up they can be less trouble.

[GILow]

Originally Posted by stillbuilding

Many engines are well balanced and contribute little vibration if hard mounted. Once well set up they can be less trouble.

So are you saying it might be a plus for reliability the way it is mounted?

Matt

[stillbuilding]

Many commercial boats are hard mounted for simplicity and robustness. I wonder if a small reason for this might be that the engine is less inclined to be thrown about if a net least line is caught by the prop?
I have owned a couple of boats that came hard mounted and they required very little input over time. I would not change the present arrangement if it works.

If vibration is big issue for some reason then by all means change. Some vibration might be more concerning in a charter yacht where guests want to sleep. I can sleep almost anywhere and maybe even feel more about the boat from the usual working noises. Some are obsessive about eliminating every squeak and tremor.

[charliehows]

my engine is hard mounted, i mentioned it to a very experienced (and old) sailing guru i occasionally get to chat to, all he said was "thats the best way" - theres a bit of vibe but it doesnt bother me much and his comment dismissed the idea i had been considering of converting it to soft mounts (at considerable expense). Its been running since 1978, cant be too bad a design. Your question about why it was done that way - maybe at the time it was built that was considered the best way.

[DeepFrz]

I think its because you guys are upside down and he didn't want the engine to fall out...

We don't have that problem up here...

[charliehows]

well even if it did up there you'd just pick it up off the ice and put it back...

[olympia]

Howdy, my Swanson 32 built in 1973 has a Volvo MD2B which is also hard mounted. Perhaps the Swanson Brothers just preferred this arrangement: KISS?

Cheers,

Paul

[ccgarnaal]

I would stay with hard mounted for reliability if you don't have excessive vibrations. Soft mounts wear and have to be replaced over time.
A proper hard mount is slightly more picky on alignment but can last forever.

My engine is hard mounted (1962) I loosened the shaft coupling and check the alignment when I bought the boat it was correct to 0.001mm after 50 years.

I still haven't seen any soft mounts lasting 50 years.